- Oxathiirane
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We describe the first preparation of the long-sought parent oxathiirane from sulfine through photochemical rearrangement with light at λ = 313 ± 10 nm in an Ar matrix at 11 K. Oxathiirane was characterized by the extraordinarily good agreement of experime
- Schreiner, Peter R.,Reisenauer, Hans Peter,Romanski, Jaroslaw,Mloston, Grzegorz
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- Hexagonal Orthovanadates as Catalysts in the Oxidation of Methanol to Formaldehyde
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Improved selectivities are obtained in the catalytic oxidation of methanol to formaldehyde using hexagonal orthovanadates of the type Sr3-xLa2x/3(VO4)2 (x=0.3-1.5) in comparison with those using the strontium and lanthanum orthovanadates separately.
- Salagre, Pilar,Sueiras, Jesus E.
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- Selective Photooxidation of Light Alkanes to Oxygenates using Supported Molybdenum Oxide Catalysts
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Photo-assisted catalytic partial oxidation of methane, ethane and propane has been performed in the presence of supported molybdenum oxide catalysts at around 500 K by the use of a fluidized bed flow-type reactor under UV irradiation.Temperatures as high as 500 K were indispensable for the selective formation of methanal from methane (ca. 19 μmol h-1), corresponding to 5.5percent of the photons irradiated into the catalyst bed (-1) at elevated temperature.The reaction seemed to proceed via charge-transfer complexes formed by photo-activation of terminal coordinatively unsaturated M=O groups in multilayers of molybdenum species.
- Wada, Kenji,Yoshida, Kyomi,Watanabe, Yoshihisa
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- Kinetics and mechanism of the reaction of CH3O with NO
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The kinetics of the reaction of CH3O with NO and the branching ratio for HCHO product formation, obtained as ΓHCHO = (Rate of HCHO formation) / (Rate of CH3O decay), have been studied using a discharge flow reactor. Laser induced fluorescence has been used to monitor the decay of the CH3O radical and the build-up of the HCHO product. Overall rate constants and product branching ratios were measured at room temperature over the pressure range of 0.72-8.5 torr He. Three reaction mechanisms were considered which differed in the routes of HCHO formation: (i) direct disproportionation; (ii) via an energized collision complex; or (iii) both reaction routes. It has been shown that data on the pressure dependence of the overall rate constant are not sufficient to distinguish between these mechanisms. In addition, an accurate value of ΓHCHO∞ is required. Analysis of the available experimental data provided 0.0 and about 0.1 as the lower and upper limit for ΓHCHO∞, respectively. Since the rate constants derived for CH3ONO formation were not sensitive to the value assumed for ΓHCHO∞, kCH(3)ONO0 = (1.69 ± 0.69) × 10-29 cm6 molecule-2 s-1 and kCH(3)ONO∞ = (2.45 ± 0.31) × 10-11 cm3 molecule-1 s-1 could be derived. The rate constant obtained for formaldehyde formation when extrapolated to zero pressure is kHCHO0 = (3.15 ± 0.92) × 10-12 cm3 molecule-1 s-1.
- Dobe,Lendvay,Szilagyi,Berces
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- Kinetics and Mechanism of Methanol Oxidation in Supercritical Water
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We oxidized methanol in supercritical water at 246 atm and temperatures between 500 and 589 deg C.Pseudo-first-order rate constants calculated from the data led to Arrhenius parameters of A = 1021.3 +/- 5.3 s-1 and Ea = 78 +/- 20 kcal/mol.The induction time for methanol oxidation decreased from 0.54 s at 525 deg C to 0.093 s at 585 deg C and the reaction products were formaldehyde, CO, and CO2.Formaldehyde was a primary product, while CO and CO2 were secondary products.Formaldehyde was more reactive than methanol and its yield was always less than 24percent.The temporal variation of the CO yield exhibited a maximum, whereas the CO2 yield increased monotonically.The experimental data were consistent with a set of consecutive reactions (CH3OH -> CH2O -> CO -> CO2) with pseudo-first-order global kinetics.The experimental data were also used to validate a detailed chemical kinetics model for methanol oxidation in supercritical water.With no adjustments, this elementary reaction model quantitatively predicts the product distribution as a function of the methanol conversion, and it accurately predicts that this distribution is nearly independent of temperature.A sensitivity analysis revealed that only eight elementary reaction steps most strongly influenced the calculated species' concentrations.A reaction path analysis showed that the fastest reactions that consumed methanol involved OH attack and the resulting radicals produced formaldehyde, which was attacked by OH to form, eventually, CO.The CO was then oxidized to CO2 via rection with OH.This work shows that the chemistry for methanol oxidation in supercritical water at temperatures around 500-600 deg C is quantitatively analogous to combustion chemistry within the same temperature range.
- Brock, Eric E.,Oshima, Yoshito,Savage, Phillip E.,Barker, John R.
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- Improved anticonvulsant activity of phenytoin by a redox brain delivery system II: Stability in buffers and biological materials
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The stability of nine chemical delivery systems (CDSs) for phenytoin (DPH) was studied in aqueous buffers and in biological materials. The systems were based on a dihydropyridune ? quaternary pyridinium salt redox pair attached to 3-(hydroxymethyl)phenytoin via an ester linkage. The pyridinium derivatives released DPH in aqueous buffers and their hydrolytic reactivity was consistent with their chemical structure. Although in rat blood and plasma all pyridinium esters hydrolyzed rapidly, there was a wide range in the hydrolysis rates in rat brain homogenate. The sterically hindered 1-alkylcarboxynicotinamide was the least reactive ester (t( 1/2 ) = 98.2 min), while the trigonellylglycolate ester was the fastest to hydrolyze enzymatically (t( 1/2 ) = 2 min) in rat brain homogenate. In acidic media, the major products of all dihydropyridine esters were the corresponding water adducts, the 6-hydroxy-1,4,5,6-tetrahydropyridines. These adducts were of no significance in biological materials. After comparison of the relative stability of the corresponding pairs of dihydropyridine and pyridinium ion in brain homogenate and the absolute stability of the various dihydropyridines, two CDSs were chosen for further in vivo evaluations. The CDSs chosen were the dihydrotrigonellinate ester and its 6-methyl derivative.
- Murakami,Shek,Pop,Bodor
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- Oxidative degradation of norfloxacin by a lipophilic oxidant, cetyltrimethylammonium permanganate in water-acetonitrile medium: A kinetic and mechanistic study
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The present study reports the oxidative metabolism of an established antibacterial drug norfloxacin (NRF) by a lipid compatible lipophilic Mn(VII) oxidant, cetyltrimethylammonium permanganate (CTAP) in acetonitrile-water binary mixture in the presence of acetic acid. The metabolized products are identified as 7-amino-1-ethyl-6-fluoro-1,4-dihydro-4-oxoquinoline-3-carboxylic acid, formaldehyde, and ammonia. The kinetics of the reaction is studied in aqueous acetonitrile media in the presence of acetic acid by UV-vis spectroscopic method by monitoring the absorbance of Mn(VII) at 530 nm under pseudo first-order condition. The reaction is found to be first-order with respect to CTAP and fractional order with respect to norfloxacin and acetic acid. Occurrence of Michaelis-Menten type kinetics with respect to norfloxacin confirmed the binding of oxidant and substrate to form a complex before the rate determining step. A suitable ionic mechanism is proposed based on the experimental findings. The proposed reaction mechanism is supported by the effect of solvent polarity and effect of temperature on the reaction rate. High negative entropy of activation (ΔS≠ = - 259 to - 158 J K- 1 mol- 1) supported the existence of a forced, more ordered and extensively solvated transition state. Further, solvent polarity-reactivity relationship revealed (i) the presence of less polar transition state compared to the reactants, (ii) differential contribution from dipolar aprotic (acetonitrile) and polar protic (water) solvents toward the reaction process through specific and nonspecific solute-solvent interaction and (iii) presence of intramolecular H-bonding in oxidant-substrate complex in acetonitrile rich domain and intermolecular H-bonding between oxidant-substrate complex and water in water rich domain.
- Garnayak, Sarita,Patel, Sabita
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- The ethene-ozone reaction in the gas phase
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The ethene-ozone reaction was investigated in a 570 L spherical glass reactor at atmospheric pressure, using long-path FTIR spectroscopy for detection of the individual products. Experiments were performed in the presence of hydroxy and carbonyl compounds to identify the reactions of the Criegee intermediate CH2OO formed in ethene ozonolysis. Using 13C-labeled HCHO, this reaction was found to proceed via an unstable cyclic adduct which decays to the detected products HCHO, HCOOH and CO. [CH2OO + HCHO → HCHO + HCOOH (eq 13); CH2OO + HCHO → HCHO + CO + H2O (eq 14a); CH2OO + HCHO → HCHO + HCO + OH (eq 14b)] The relative rates of the reactions of CH2OO with HCOOH and HCHO were determined from the product analysis. In addition, evidence was found that the reaction of CH3CHO with the CH2OO intermediate does not exclusively produce secondary propene ozonide, but also HCHO and CO2. The results of this study have been combined with data from previous investigations to give a complete description of the gas phase ozonolysis of ethene and are discussed in comparison with ozonolysis reactions occurring in the liquid phase.
- Neeb, Peter,Horie, Osamu,Moortgat, Geert K.
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- Elucidation of the 1,4-dioxane decomposition pathway at discrete ultrasonic frequencies
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The sonolytic decomposition chemistry of the refractory compound 1,4-dioxane in aqueous solution has been investigated at four ultrasonic frequencies (205, 358, 618, and 1071 kHz). To maintain fully saturated solutions, argon and oxygen were used as sparge gases. Using a frequency of 358 kHz, the observed first-order kinetic rate constants for 1,4-dioxane destruction were highest with a sparge gas ratio of 75% Ar/25% O2 (k = 4.32 ± 0.31 x 10-4 s-1) and lowest in the presence of pure argon (k= 8.67 ± 0.47 x 10-5 s-1). Ethylene glycol diformate, methoxyacetic acid, formaldehyde, glycolic acid, and formic acid were found to be the major intermediates of 1,4-dioxane degradation. A reaction mechanism involving these byproducts was proposed concerning primarily reactions with oxidizing species (·OH, ·OOH, ·O) in and near the interfacial region of the cavitation bubble. The highest observed first-order 1,4-dioxane decomposition rate occurred at 358 followed by 618, 1071, and 205 kHz. At each frequency, approximately 85% of the initial carbon is accounted for as the parent compound, as an intermediate, or as CO2. The major byproducts formation was investigated at all four frequencies, and the results indicate that free radical mechanisms are significant over the entire range of frequencies studied. The sonolytic decomposition chemistry of the refractory compound 1,4-dioxane in aqueous solution has been investigated at four ultrasonic frequencies (205, 358, 618, and 1071 kHz). To maintain fully saturated solutions, argon and oxygen were used as sparge gases. Using a frequency of 358 kHz, the observed first-order kinetic rate constants for 1,4-dioxane destruction were highest with a sparge gas ratio of 75% Ar/25% O2 (k = 4.32 ± 0.31 × 10-4 s-1) and lowest in the presence of pure argon (k = 8.67 ± 0.47 × 10-5 s-1). Ethylene glycol diformate, methoxyacetic acid, formaldehyde, glycolic acid, and formic acid were found to be the major intermediates of 1,4-dioxane degradation. A reaction mechanism involving these byproducts was proposed concerning primarily reactions with oxidizing species (·OH, ·OOH, ·O) in and near the interfacial region of the cavitation bubble. The highest observed first-order 1,4-dioxane decomposition rate occurred at 358 followed by 618, 1071, and 205 kHz. At each frequency, approximately 85% of the initial carbon is accounted for as the parent compound, as an intermediate, or as CO2. The major byproducts formation was investigated at all four frequencies, and the results indicate that free radical mechanisms are significant over the entire range of frequencies studied.
- Beckett,Hua
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- Quantitative measurements of HO2 and other products of n -butane oxidation (H2O2, H2O, CH2O, and C2H4) at elevated temperatures by direct coupling of a jet-stirred reactor with sampling nozzle and cavity ring-down spectroscopy (cw-CRDS)
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For the first time quantitative measurements of the hydroperoxyl radical (HO2) in a jet-stirred reactor were performed thanks to a new experimental setup involving fast sampling and near-infrared cavity ring-down spectroscopy at low pressure. The experiments were performed at atmospheric pressure and over a range of temperatures (550-900 K) with n-butane, the simplest hydrocarbon fuel exhibiting cool flame oxidation chemistry which represents a key process for the auto-ignition in internal combustion engines. The same technique was also used to measure H2O2, H2O, CH2O, and C2H4 under the same conditions. This new setup brings new scientific horizons for characterizing complex reactive systems at elevated temperatures. Measuring HO2 formation from hydrocarbon oxidation is extremely important in determining the propensity of a fuel to follow chain-termination pathways from R + O2 compared to chain branching (leading to OH), helping to constrain and better validate detailed chemical kinetics models.
- Djehiche, Mokhtar,Le Tan, Ngoc Linh,Jain, Chaithanya D.,Dayma, Guillaume,Dagaut, Philippe,Chauveau, Christian,Pillier, Laure,Tomas, Alexandre
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- Atmospheric Degradation of CH2=C(CH3)C(O)OCH3 Initiated by OH Radicals: Mechanistic Study and Quantification of CH3C(O)C(O)OCH3 in NOx Free Air
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The product distribution of the gas-phase reaction of OH radicals with methyl methacrylate (CH2=C(CH3)C(O)OCH3, MMA) in the absence of NOx was studied at 298 K and atmospheric pressure of air. The experiments were performed in a Teflon chamber using solid-phase microextraction (SPME) with GC-MS and GC-FID for product identification and quantification, respectively. In the absence of NOx, methyl pyruvate (CH3C(O)C(O)OCH3) was identified with a yield of 76 ± 13% in accordance with the decomposition of the 1,2-hydroxyalkoxy radicals formed. In addition, a detailed quantum chemical study of the degradation of MMA was performed by density functional theory (DFT) methods using the MPWB1K functional. This calculation suggests that formation of methyl pyruvate, from C1-C2 scission of 1,2-hydroxyalkoxy radical, is kinetically and thermodynamically the most favorable reaction path taking into account the electronic properties of reaction intermediates and transition states. The difference observed on the degradation mechanism of MMA in the presence and absence of NOx was explained in terms of the associated thermochemistry. Furthermore, this study propose that reaction between peroxy radical (RO2?) and hydroxyl radical (OH) became relevant at NOx-free environments. This statement is in agreement with recent studies concerning small peroxy radicals such as CH3OO?.
- Gibilisco, Rodrigo G.,Uranga, Jorge G.,Santiago, Ana N.,Teruel, Mariano A.
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- μ-Nitrido-bridged iron phthalocyanine dimer bearing eight peripheral 12-crown-4 units and its methane oxidation activity
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A novel μ-nitrido-bridged iron phthalocyanine dimer with eight peripheral 12-crown-4 units as an electron-donating substituent was synthesized and characterized. Examination of its methane oxidation activity in the presence of H2O2 in an acidic aqueous solution suggested that the high-valent iron oxo species generated in situ was unstable and the transiently generated decomposed species showed methane oxidation activity via Fenton-type reaction. This journal is
- Yamada, Yasuyuki,Kura, Jyunichi,Toyoda, Yuka,Tanaka, Kentaro
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- Nitrous Oxide in Gas-Phase Ion-Molecule Chemistry: A Versatile Reagent for the Determination of Carbanion Structure
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Nitrous oxide has been found to undergo a wide variety of reactions with anions in the gas phase.The products of these reactions are highly characteristic of the ion's structure and, therefore, this reagent (N2O) is especially useful in distinguishing between different types of ions.In general, primary carbanions react to produce diazo anions as the major products, secondary carbanions dehydrogenate, and tertiary carbanions afford adducts, oxygen atom transfer, and cleavage products.However, novel reaction channels can be brought about by modifying the reactant ion's structures.For example, deprotonation of methylene cyclopropane produces a strained allylic anion which reacts with N2O to afford cyanide and the 2-nitrosoallyl anion, while removal of a proton from furan, which has a good α-leaving group, generates the nitrogen atom transfer product, 3-cyanoacrolein radical anion, upon reaction with N2O.It was observed that proton abstraction from cyclopentene, cyclohexene, and internal olefins without allylic methyl groups does not afford M - 1 ions in the flowing afterglow.
- Kass, Steven, R.,Filley, Jonathan,Doren, Jane M. Van,DePuy, Charles H.
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- Effect of the Addition of Nitrogen Dioxide on the Gas-Phase Partial Oxidation of Methane with Oxygen under Normal Pressures
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The addition of NO2 to the gas-phase reaction of CH4 with O2 conducted under normal pressures at temperatures of 400-460 deg C enhances the partial oxidation of methane with improved selectivities to organic products.
- Han, Li-Biao,Tsubota, Susumu,Haruta, Masatake
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- Kinetics of oxidation of methane to formaldehyde on Na 4[PFeMo11O40]/SiO2
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The kinetics of oxidation of CH4 to formaldehyde on the catalytic system Na4[PFeMo11O40]/SiO 2 were studied, and a significant role of the redox potential of the CH4-O2 system with respect to the catalyst was shown. The density of centers participating in the reaction was determined, and dissociative competitive adsorption of methane and oxygen was established. The equation was deduced in the framework of the Langmuir-Hinshelwood theory taking into account the side conversion of formaldehyde. Possible participation of lattice oxygen in the reaction was suggested.
- Marakaev,De Vekki
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- Photoinduced Reactions of Methane with Molybdena Supported on Silica
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Photoinduced reactions of methane on the surface on molybdena-silica have been studied using u.v. irradiation in the temperature range 293-773 K.During irradiation, photoadsorption of methane (up to 300 mmol of CH4 per mol of Mo) is found to be the predominant process with barely detectable formation of gaseous products.During heating of the irradiated samples from 293 to 473 K, in addition to thermodesorption of methane, wich reaches 40-50percent of photoadsorbed CH4, the desorption of considerable amounts of ethylene, ethane, hydrogen and smaller amounts of C3 and C4 alkenes and alkanes is observed.E.s.r., u.v.-visible and i.r. measurements of the irradiated samples show the presence of Mo5+ and Mo4+ ions as well as complexes of Mo4+ with olefins.The effects of O2, N2O and H2O on the photoinduced reactions of methane and on thermodesorption of the products have also been studied.Possible reaction mechanisms for the photoadsorption of methane and for the formation of C2 and higher hydrocarbons are discussed.
- Hill, Wieland,Shelimov, Boris N.,Kazansky, Vladimir B.
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- Complexation and Oxidation of Glycine and Related Compounds by Ag(II)
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The oxidation of glycine, several other amino acids, and carboxylic acids by Ag(II) has been studied.Transient spectra, kinetics, and product analysis indicate that the mechanism involves two steps.The first step is formation of a complex between Ag(II) and the substrate.The second step is an electron transfer from the carboxyl group to the Ag(II) within the complex.As a result, the substrate undergoes decarboxylation.The rate constants for complexation and oxidation were determined for a variety of substrates and with different forms of Ag(II), i.e., aquo, hydroxo, and ammino complexes.Both steps of the mechanism are affected by the structure of the substrate, for example, by the electron-donating properties of methyl groups and electron withdrawing by the NH3+ group.The rate of electron transfer within the complex is also affected by the structure and stability of the complex.The rate constants for complexation of the compounds studied under various conditions range from 106 to 108 M-1 s-1.The rates of oxidation were usually of the order of 103 s-1, although the highly stable complexes reacted more slowly.
- Kumar, Anil,Neta, P.
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- In operando imaging of self-catalyzed formaldehyde burst in methanol oxidation reactions under open circuit conditions
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We employ a surface plasmon resonance imaging (SPRi) technique to monitor the in operando process of formaldehyde (HCHO) production during methanol oxidation with high spatial and temporal resolutions. While common wisdom suggests HCHO is generated as an intermediate during continuous electron transfer towards CO2, we find that the majority of HCHO is produced via self-catalyzed chemical and electrochemical reactions under open-circuit conditions, which lead to an unprecedented HCHO burst immediately after withdrawal of external potential. Because open-circuit conditions better represent the operating environments of practical direct methanol fuel cells (DMFCs), this work uncovers a hidden pathway of HCHO accumulation by adopting a quantitative and in operando SPRi technique for the first time. These theoretical and technical advances are anticipated to help the fundamental understanding of the comprehensive mechanism of methanol oxidation with implications for improving the performance of DMFCs.
- Yuan, Liang,Li, Meng,Yuan, Tinglian,Fang, Yimin,Wang, Wei
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- EFFECTS OF METHYLATION ON THE THERMAL STABILITY AND CHEMILUMINESCENCE PROPERTIES OF 1,2-DIOXETANES.
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The unknown monomethyl derivative 1f and the parent 1,2-dioxetane 1g have been prepared and fully characterized. The influence of the degree and pattern of methyl substitution of the complete set of 1,2-dioxetanes 1a-g on the activation parameters ( DELTA H** DOUB DAG , DELTA S** DOUB DAG , and DELTA G** DOUB DAG ) and on the excitation yields ( phi **T and phi **S) have been determined. It was found that (1) the thermal stability increases with the degree of methylation, (2) the pattern of methylation does not alter appreciably thermal stability, (3) triplet n, pi * states are preferentially energized, and (4) the triplet and singlet excitation yields increase with the degree of methylation. These experimental results are compared with thermochemical estimates and rationalized in terms of the diradical hypothesis and energy surface crossings.
- Adam,Baader
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- Kinetics of Methanol Oxidation Over Platinum Wire Catalysts
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The oxidation of methanol at atmospheric pressure over platinum wire catalysts has been studied over a wide range of experimental conditions (T = 310-660 K, PO2/PCH3OH = 2-100).Two experimental techniques were used.In the conventional flow-reactor experiments kinetic parameters were obtained from measurement of gas-phase concentrations, while in the microcalorimeter experiments kinetic parameters were derived from the rates of heat generation at the catalyst surface.At 373 K, for PO2/PCH3OH = 25, a point within the experimental range common to both techniques, the specific rates of oxidation determined by each method were 120 nmols-1cm-2 (conventional flow reactor) and 100 nmols-1cm-2 (microcalorimeter).The use of the microcalorimeter enabled kinetic measurements to be made over the full experimental range.It was found that the observed kinetics were dependent on both temperature and oxygen:methanol ratio.Thus in the general rate expression: R = k*Pm(CH3OH)*Pn(O2) the values of m and n were found to vary between 0 and 0.5 (PO2/PCH3OH O2/PCH3OH = 8-15, T = 325-390 K), to 1 and 0 (T > 405 K, all ratios).Non-steady-state kinetics were also observed for PO2/PCH3OH = 5 at temperatures between 380 and 405 K.A mechanism, which is consistent with the observations, is proposed involving the interaction of gaseous methanol with adsorbed atomic oxygen to produce adsorbed methoxy species.These species react with further oxygen to produce formaldehyde or carbon dioxide.
- Gentry, Stephen J.,Jones, Alan,Walsh, Peter T.
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- Photocatalytically assisted hydrolysis of chlorinated methanes under anaerobic conditions
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The photocatalytic degradation of CCl4, CHCl3, and CH2-Cl2 over irradiated Ti02 has been investigated at pH 5 and pH 11 under anaerobic conditions. Chloromethanes degrade through combined reductive and oxidative processes. Photocatalytically assisted hydrolysis, given by sequential reactions involving ·OH/e-/H+, is 106-108 times faster than the corresponding thermal process. Dechlorination of chloromethanes is achieved with degradation rates in the order CCl4 > CHCl3 > CH2Cl2. Stable intermediates, either chlorinated (chloromethanes, C2Cl6, and C2Cl4) or dechlorinated (formic acid, formaldehyde, and methanol) have been quantified. The average carbon oxidation number n(c) remains almost unchanged at the end of the degradation process, although for CCl4 in the early stages it is markedly reduced with slow regrowth of n(c) toward the initial value. Reaction pathways accounting for the observed results are presented based on literature data concerning transient intermediates. The photocatalytic degradation of CCl4, CHCl3, and CH2-Cl2 over irradiated TiO2 has been investigated at pH 5 and pH 11 under anaerobic conditions. Chloromethanes degrade through combined reductive and oxidative processes. Photocatalytically assisted hydrolysis, given by sequential reactions involving ·OH/e-/H+, is 106-108 times faster than the corresponding thermal process. Dechlorination of chloromethanes is achieved with degradation rates in the order CCl4>CHCl3>CH2Cl2. Stable intermediates, either chlorinated (chloromethanes, C2Cl6, and C2Cl4)or dechlorinated (formic acid, formaldehyde, and methanol) have been quantified. The average carbon oxidation number nc remains almost unchanged at the end of the degradation process, although for CCl4 in the early stages it is markedly reduced with slow regrowth of nc toward the initial value. Reaction pathways accounting for the observed results are presented based on literature data concerning transient intermediates.
- Calza, Paola,Minero, Claudio,Pelizzetti, Ezio
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- Low-temperature and Direct Synthesis of Ethanol from Ethane and Water by the Photochemical Reaction
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Ethane is directly converted to ethanol by the photochemical reaction at temperatures lower than 100 deg C in atmospheric pressure.The conversion reaction is initiated by the hydroxyl radicals formed in the photolysis of water vapor.The conversion coefficient of ethane was 7.7 percent at 5 h and the selectivity 33.3 percent.
- Ogura, Kotaro,Arima, Hiroaki
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- Methylperoxy Self-Reaction: Products and Branching Ratio between 223 and 333 K
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Products from Cl atom initiated oxidation of CH4 were analyzed by matrix isolation Fourier transform infrared spectroscopy (MI-FTIR) in order to determine the branching ratio k1a/k1 of the methylperoxy self-reaction: CH3O2 + CH3O2 -> CH3O + CH3O + O2 (1a); CH3O2 + CH3O2 -> HCHO + CH3OH + O2 (1b); and CH3O2 + CH3O2 -> CH3OOCH3 + O2 (1c).The value k1a/k1 = k1a/(k1a+k1b+k1c) showed a pronounced temperature dependence in the range 223 - 333 K and is given by the relationship k1a/k1 = 1/ /(19 +/- 5)>.These results are combined with previous measurements to make a recommendation for the temperature range 223 - 573 K: k1a/k1 = 1//(33 +/- 10)>.
- Horie, O.,Crowley, J. N.,Moortgat, G. K.
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- Direct conversion of methane into formaldehyde mediated by [Al 2O3].+ at room temperature
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Just one step: Reactivity studies demonstrate that in the gas phase [Al2O3].+ clusters can efficiently conduct the direct conversion of CH4 into CH2O at room temperature (see scheme). The reaction mechanism is highly complex involving oxygen-atom transfer and a double hydrogen-atom transfer.
- Wang, Zhe-Chen,Dietl, Nicolas,Kretschmer, Robert,Ma, Jia-Bi,Weiske, Thomas,Schlangen, Maria,Schwarz, Helmut
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- Selective photo-assisted catalytic oxidation of methane and ethane to oxygenates using supported vanadium oxide catalysts
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Selective photooxidation of light alkanes, mainly methane and ethane, into the corresponding aldehydes was achieved using silica-supported vanadium oxide catalysts under UV irradiation at elevated temperature. Photooxidation of methane using the V2O5/SiO2-IW (incipient wetness) (0.6 mol% V) catalyst at 493 K for 2 h gave 68 μmol of methanal, which corresponds to 76 mol% selectivity and 0.48 mol% one-pass yield. Photooxidation of ethane using V2O5/SiO2 (calcined at 1023 K) -IW (0.6 mol% V) catalyst for 1 h gave 85 μmol of ethanal, which corresponds to 90% selectivity and 1.1% one-pass yield. The catalysts prepared by the sol-gel method also showed activity, especially for the reaction of ethane. Both UV irradiation and a reaction temperature as high as 500 K were essential. The photo-assisted catalytic reactions were very sensitive to the reaction temperature, method of preparation of the catalyst, and addition of water vapour. While the reaction of methane was inhibited by the addition of water vapour, the photooxidation of ethane and propane was promoted in the presence of a controlled amount of water vapour. In addition, the reaction with methane required UV irradiation at a wavelength 2O5, were shown to be active for the photooxidation of ethane and propane.
- Wada, Kenji,Yamada, Hiroshi,Watanabe, Yoshihisa,Mitsudo, Take-Aki
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- Sonochemical Transformations of Methane and Ethylene in Aqueous Solutions under Conditions of Cavitation
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Abstract: The conversion of methane, ethylene and mixtures of them in aqueous solutions was studied using ultrasonic vibrations with a frequency of 22 kHz under conditions of cavitation. It is found that formaldehyde, the main product, forms even if there is no dissolved oxygen in the initial solution. It is shown that the rate of accumulation of formaldehyde depends on the power of the ultrasound and the amount of molecular oxygen introduced into the system.
- Arsentev, S. D.
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- Photocatalytic Hydrogen Evolution from Alcohols using Dodecawolframosilicic Acid and Colloidal Platinum
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Illumination of dodecawolframosilicic acid and colloidal platinum leads to photocatalytic H2 evolution from alcohols with a quantum yield for H2 of 0.1 mol einstein-1.
- Darwent, James R.
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- Pd-Catalyzed Surface Reactions of Importance in Radiation Induced Dissolution of Spent Nuclear Fuel Involving H2
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To assess the influence of metallic inclusions (?-particles) on the dissolution of spent nuclear fuel under deep repository conditions, Pd-catalyzed reactions of H2O2, O2 and UO2 2+ with H2 were studied using Pd-powder suspensions. U(VI) can efficiently be reduced to less soluble U(IV) on Pd-particles in the presence of H2. The kinetics of the reaction was found to depend on the H2 partial pressure at pH2≤5.1×10?2 bar. In comparison, the H2 pressure dependence for the reduction of H2O2 on Pd also becomes evident below 5.1×10?2 bar. Surface bound hydroxyl radicals are formed as intermediate species produced during the catalytic decomposition of H2O2 on oxide surfaces. While a significant amount of surface bound hydroxyl radicals were scavenged during the catalytic decomposition of H2O2 on ZrO2, no scavenging was observed in the same reaction on Pd. This indicates a different reaction mechanism for H2O2 decomposition on Pd compared to metal oxides and is in contrast to current literature. While Pd is an excellent catalyst for the synthesis of H2O2 from H2 and O2, a similar catalytic activity that was previously proposed for ZrO2 could not be confirmed.
- Maier, Annika Carolin,Jonsson, Mats
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- Amphiphilic/bipolar metallocorroles that catalyze the decomposition of reactive oxygen and nitrogen species, rescue lipoproteins from oxidative damage,and attenuate atherosclerosis in mice
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(Chemical Equation Presented) Antioxidans that work! The iron corrole 1-Fe (see picture) is a potetnt catalyst for decomposition of reactive oxygen and nitrogen species that binds selectively to lipoproteins. The complex also affects cholesterol levels and its cellular efflux. 1-Fe is more effective that natural antioxidants in reducing atherosclerosis development in mice. LDL = low-density lipoprotein.
- Haber, Adi,Mahammed, Atif,Fuhrman, Bianca,Volkova, Nina,Coleman, Raymond,Hayek, Tony,Aviram, Michael,Gross, Zeev
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- Concurrent electrophilic and oxidative pathways for reactions of α-hydroxyalkyl and α-alkoxyalkyl complexes of chromium(III) with mercury(II) ions
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The reactions of Hg2+ with a number of α-hydroxyalkyl and α-alkoxyalkyl complexes of chromium(III) were studied. The lowest members of both series, CrCH2OH2+ and CrCH2OCH32+, react with Hg
- Espenson, James H.,Bakac, Andreja
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- High catalytic methane oxidation activity of monocationic μ-nitrido-bridged iron phthalocyanine dimer with sixteen methyl groups
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Herein, we report the highly potent catalytic methane oxidation activity of a monocationic μ-nitrido-bridged iron phthalocyanine dimer with 16 peripheral methyl groups. It was confirmed that this complex oxidized methane stably into MeOH, HCHO, and HCOOH in a catalytic manner in an acidic aqueous solution containing excess H2O2 at 60 °C. The total turnover number of the reaction reached 135 after 12 h, which is almost seven times higher than that of a monocatinoic μ-nitrido-bridged iron phthalocyanine dimer with no peripheral substituents. This suggests that the increased number of peripheral electron-donating substituents could have facilitated the generation of a reactive high-valent iron-oxo species as well as hydrogen abstraction from methane by the reactive iron-oxo species.
- Kura, Jyunichi,Tanaka, Kentaro,Toyoda, Yuka,Yamada, Yasuyuki
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- THE EFFECT OF ETHANOL ON THE CATALYTIC OXIDATION OF METHANOL ON SILVER
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Thermal desorption, radioactive indicators, and a kinetic method involving frozen radicals were used to study the catalytic oxidation of methanol in the presence of ethanol on silver.The increase in the yield of aldehydes in the combined oxidation of these alcohols on silver is related to a change in the nature of the adsorption and homogeneous steps of this reaction.
- Filicheva, O. D.,Kurina, L. N.,Zeile, L. A.,Garibyan, T. A.,Grigoryan, R. R.
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- Reactions of C2H5 Radicals with O, O3, and NO3: Decomposition Pathways of the Intermediate C2H5O Radical
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The reactions of C2H5 with O, O3, and NO3 have been investigated in a discharge flow reactor at room temperature and pressures between 1 and 3 mbar. The reaction products were detected by mass spectrometry with electron-impact ionization. The product pattern observed is explained in terms of the decomposition of an intermediately formed, chemically activated ethoxy radical. It is shown that, with this assumption, the experimentally determined branching ratios of the different product channels can be reproduced nearly quantitatively by RRKM calculations based on ab initio results for the stationary points of the potential energy surface of C2H5O. For C + O and C2H5 + O3, the existence of an additional, parallel channel leading to OH has to be assumed. High-pressure Arrhenius parameters for the unimolecular reactions of the ethoxy radical are given and discussed.
- Hoyermann,Olzmann,Seeba,Viskolcz
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- Photocatalytic Oxidation of Propan-2-ol by Semiconductor-Zeolite Composites
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The photocatalytic oxidation of liquid propan-2-ol to propanone has been investigated using semiconductor-zeolite composites consisting of either CdS or TiO2 in Y zeolite.CdS-based composites were prepared by cation exchange with Cd2+ followed by sulfidation with either Na2S or H2S, whereas TiO2-based composite was prepared by Ti(OEt)4 impregnation followed by hydrolysis and calcination.Rate measurements at 303 K were made to assess how the activity of CdS-based material depended on reaction conditions; differences from CdS supported on γ-Al2O3 are ascribed to smaller CdS particles and the higher adsorption potential of the zeolite matrix for O2 and H2O.However, rate measurements under standard conditions over the temperature range 283-308 K yielded the same activation energies as for CdS and TiO2 supported on γ-Al2O3, 53 +/- 2 kJ mol-1 for CdS-based catalysts and 21 +/- 1 kJ mol-1 for TiO2-based catalysts.It follows that the physico-chemical properties of the semiconductor control the activation energy, whereas the zeolite matrix is responsible for controlling semiconductor particle size during preparation and modifying the effective reaction conditions through adsorption.
- Green, Kevin J.,Rudham, Robert
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- Thermolysis of 3-alkyl-3-methyl-1,2-dioxetanes: Activation parameters and chemiexcitation yields
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3-Methyl-3-(3-pentyl)-1,2-dioxetane 1 and 3-methyl-3-(2,2-dimethyl-1-propyl)-1,2-dioxetane 2 were synthesized in low yield by the α-bromohydroperoxide method. The activation parameters were determined by the chemiluminescence method (for 1 ΔH? = 25.0 ± 0.3 kcal/mol, ΔS? = -1.0 entropy unit (e.u.), ΔG? = 25.3 kcal/mol, k1 (60°C) = 4.6 × 10-4s-1. Thermolysis of 1-2 produced excited carbonyl fragments (direct production of high yields of triplets relative to excited singlets) (chemiexcitation yields) for 1: φT = 0.2, φ ≤ 0.0005; for 2: φT = 0.02 φS ≤ 0.0004). The results are discussed in relation to a radical-like mechanism.
- Baumstark, Alfons L.,Anderson, Sean L.,Sapp, Chariety J.,Vasquez, Pedro C.
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- Gas-Phase Reactions of Negative Ions with Alkyl Nitrites
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The gas-phase reactions of F-, NH2-, OH-, and a variety of carbanions with a series of alkyl nitrites (methyl, ethyl, n-butyl, isoamyl, and neopentyl) are reported.The reactions of F- were studied by the selected ion flow tube technique while all other reactions were examined in a conventional flowing afterglow system.For fluoride ion, E2 reactions occur exclusively for nitrites containing β-hydrogens, SN2 processes dominate for methyl nitrite, and ECO2 reactions occur for neopentyl nitrite.The high specificity of product formation is discussed in terms of potential surfaces, and reaction rate constants are compared to calculated collision rates.The reactions of carbanions with neopentyl nitrite proceed primarily by nitrosation followed by proton transfer or by nitrosation followed by a reverse Claisen-type condensation.Finally, NH2- and OH- react rapidly with most nitrites to form NO2-; NH2- reacts with neopentyl nitrite to generate HN2O-.These data are compared and contrasted to some recent results from ion cyclotron resonance experiments.
- King, Gary K.,Maricq, M. Matti,Bierbaum, Veronica M.,DePuy, Charles H.
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- Direct dehydrogenation of methanol to formaldehyde over novel Ag-containing ceramics
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A novel silver-ceramics supported catalyst showing excellent activity and selectivity in the direct dehydrogenation of methanol to formaldehyde was prepared. The selectivity was as high as 100% and the yield of formaldehyde reached 70%.
- Dong, Yi,Dai, Wei-Lin,Li, Jia-Liang,Deng, Jing-Fa
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- Absorption Spectra of Contact-Charge-Transfer Bands and Photochemical Reactions of Simple Alkenes in the Cryogenic Oxygen Matrix
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The UV-vis absorption spectra and photochemistry of alkene-oxygen pairs in solid oxygen at 10 K have been studied.The contact-charge-transfer (CCT) bands well separated from the intrinsic absorption bands of isolated alkenes were recorded with the maxima at 218, 243, 234, 235, 263, and 287 nm for propene, 2-methylpropene (MP), cis-2-butene (CB), trans-2-butene (TB), 2-methyl-2-butene (MB), and 2,3-dimethyl-2-butene (DMB), respectively.The vertical transition energy correlated linearly with the ionization potential of the alkenes.Photochemical reaction products in the excitation within the CCT bands were studied by using FTIR.The reaction in the ion pair state can be classified into the following four pathways: (i) photooxygenation to give an oxygen adduct, which is observed only for DMB; (ii) cis-trans isomerization, which is the major reaction path for CB and TB, suggesting the crossing to the alkene triplet state; (iii) double-bond scission to give two corresponding carbonyl compounds, which is observed for all alkenes studied with energy threshold higher than the photooxygenation and cis-trans isomerization; (iv) formation of CO2, CO, and O3, which occurs at still shorter wavelength than the double-bond scission.In the case of ethene and propene, HO2 was also produced.Relevance of the present results to those in the CCT photochemistry in the oxygen-saturated organic liquid and on the semicinductor surfaces has been discussed.
- Hashimoto, Satoshi,Akimoto, Hajime
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- Pt+-catalyzed oxidation of methane: Theory and experiment
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The oxidation of methane with molecular oxygen using the atomic platinum cation as a catalyst, yielding methanol, formaldehyde, and higher oxidation products, has been studied both computationally and experimentally. The most relevant reaction pathways have been followed in detail. To this end a large number of stationary points, both minima and transition states, have been optimized using a hybrid density functional theory method (B3LYP). At these optimized geometries, energies have been calculated using both an empirical scaling scheme (PCI-80) and the B3LYP method employing extended basis sets with several polarization functions. Good agreement with available experimental data has been obtained. For the parts of the catalytic cycle where detailed experimental results have not been available, the new calculated results have complemented the experimental picture to reach an almost complete understanding of the reaction mechanisms. Spin-orbit effects have been incorporated using an empirical approach, which has lead to improved agreement with experiments. The new FTICR experiments reported in the present study have helped to clarify some of the most complicated reaction sequences.
- Pavlov, Maria,Blomberg, Margarete R. A.,Siegbahn, Per E. M.,Wesendrup, Ralf,Heinemann, Christoph,Schwarz, Helmut
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- Mechanism of the Gas-Phase Reactions of C3H6 and NO3 Radicals
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Gas-phase reactions of propylene with NO3 were investigated in the C3H6-N2O50-O2/N2 system by Fourier transform infrared spectrometry.New type of nitrogen-containing compounds, nitroxyperoxypropyl nitrate (NPPN, CH3CH(ONO2)CH2(OONO2) and/or CH3CH(OONO2)CH2(ONO2)) and nitroxypropyl nitrite (NPN, CH3CH(ONO2)CH2(ONO) and/or CH3CH(ONO)CH2(ONO2)) were identified for the reaction systems with and without O2, respectively.Both nitroxy conpounds were unstable, and their kinetic behaviors suggest that they are intermediate species in the formation of the final product, propylene glycol 1,2-dinitrate (PGDN).The reaction was concluded to be initiated by the addition reaction of the NO3 radical to propylene, and an overall reaction mechanism for the C3H6-N2O5 system was proposed.
- Bandow, H.,Okuda. M.,Akimoto, H.
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- Unprecedentedly high efficiency for photocatalytic conversion of methane to methanol over Au-Pd/TiO2-what is the role of each component in the system?
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Direct and highly efficient conversion of methane to methanol under mild conditions still remains a great challenge. Here, we report that Au-Pd/TiO2 could directly catalyze the conversion of methane to methanol with an unprecedentedly high methanol yield of 12.6 mmol gcat-1 in a one-hour photocatalytic reaction in the presence of oxygen and water. Such an impressive efficiency is contributed by several factors, including the affinity between Au-Pd nanoparticles and intermediate species, the photothermal effect induced by visible light absorption of Au-Pd nanoparticles, the employment of O2 as a mild oxidant, and the effective dissolution of methanol in water. More importantly, for the first time, thermo-photo catalysis is demonstrated by the distinct roles of light. Namely, UV light is absorbed by TiO2 to excite charge carriers, while visible light is absorbed by Au-Pd nanoparticles to increase the temperature of the catalyst, which further enhances the driving force of corresponding redox reactions. These results not only provide a valuable guide for designing a photocatalytic system to realize highly efficient production of methanol, but also, highlight the great promise of thermo-photo catalysis. This journal is
- Cai, Xiaojiao,Fang, Siyuan,Hu, Yun Hang
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supporting information
p. 10796 - 10802
(2021/05/14)
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- Highly selective oxidation of methane to formaldehyde on tungsten trioxide by lattice oxygen
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Photocatalytic oxidation of methane into formaldehyde in high yield and selectivity remains a grand challenge due to the ineluctable intermediates. Here, we report that a {001}, {010} and {100} facets modified tungsten trioxide photocatalyst enables an intermediate-free oxidation of methane into formaldehyde with 99.4% selectivity. A durable formaldehyde yield of 4.61 mmol g?1 can be achieved after irradiation for 30 h. Mechanism studies disclose that surface defect and reactive lattice oxygen atom are crucial for the selectivity and productivity promotion. This work provides a valid paradigm for efficient conversion of methane to formaldehyde.
- Fan, Yingying,Han, Dongxue,Jiang, Yuheng,Lu, Rongxia,Niu, Li,Pan, Guoliang,Wang, Wei,Wei, Shilei,Zhang, Peiyun,Zhu, Xianglian
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- Method for preparing formaldehyde by photocatalytic oxidation of ethylene glycol
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The invention provides a method for preparing formaldehyde from ethylene glycol by photocatalytic oxidation. According to the method, ethylene glycol is taken as a substrate, air or oxygen is taken asan oxygen source, and a C-C bond cracked product, namely, formaldehyde can be generated under illumination in presence of a catalyst. The conditions are mild, the oxidation efficiency and the productyield are high, and the air or the oxygen is taken as the oxygen source under the illumination condition, so that the method is economical, environmentally friendly and green, meets the strategy of sustainable developed energy and has broad application prospect.
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Paragraph 0007; 0033-0080
(2021/05/26)
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- A nonheme peroxo-diiron(iii) complex exhibiting both nucleophilic and electrophilic oxidation of organic substrates
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The complex [FeIII2(μ-O2)(L3)4(S)2]4+(L3= 2-(4-thiazolyl)benzimidazole, S = solvent) forms upon reaction of [FeII(L3)2] with H2O2and is a functional model of peroxo-diiron intermediates invoked during the catalytic cycle of oxidoreductases. The spectroscopic properties of the complex are in line with those of complexes formed with N-donor ligands. [FeIII2(μ-O2)(L3)4(S)2]4+shows both nucleophilic (aldehydes) and electrophilic (phenol,N,N-dimethylanilines) oxidative reactivity and unusually also electron transfer oxidation.
- Browne, Wesley R.,Giorgi, Michel,Kaizer, József,T?r?k, Patrik,Unjaroen, Duenpen,Viktória Csendes, Flóra
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supporting information
p. 7181 - 7185
(2021/06/11)
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- A chemiresistive methane sensor
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A chemiresistive sensor is described for the detection of methane (CH4), a potent greenhouse gas that also poses an explosion hazard in air. The chemiresistor allows for the low-power, low-cost, and distributed sensing of CH4 at room temperature in air with environmental implications for gas leak detection in homes, production facilities, and pipelines. Specifically, the chemiresistors are based on single-walled carbon nanotubes (SWCNTs) noncovalently functionalized with poly(4-vinylpyridine) (P4VP) that enables the incorporation of a platinum-polyoxometalate (Pt-POM) CH4 oxidation precatalyst into the sensor by P4VP coordination. The resulting SWCNT-P4VP-Pt-POM composite showed ppm-level sensitivity to CH4 and good stability to air as well as time, wherein the generation of a high-valent platinum intermediate during CH4 oxidation is proposed as the origin of the observed chemiresistive response. The chemiresistor was found to exhibit selectivity for CH4 over heavier hydrocarbons such as n-hexane, benzene, toluene, and o-xylene, as well as gases, including carbon dioxide and hydrogen. The utility of the sensor in detecting CH4 using a simple handheld multimeter was also demonstrated.
- Bezdek, Máté J.,Luo, Shao-Xiong Lennon,Ku, Kang Hee,Swager, Timothy M.
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- Surfactant-Assisted Ozonolysis of Alkenes in Water: Mitigation of Frothing Using Coolade as a Low-Foaming Surfactant
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Aqueous-phase ozonolysis in the atmosphere is an important process during cloud and fog formation. Water in the atmosphere acts as both a reaction medium and a reductant during the ozonolysis. Inspired by the atmospheric aqueous-phase ozonolysis, we herein report the ozonolysis of alkenes in water assisted by surfactants. Several types of surfactants, including anionic, cationic, and nonionic surfactants, were investigated. Although most surfactants enhanced the solubility of alkenes in water, they also generated excessive foaming during the ozone bubbling, which led to the loss of products. Mitigation of the frothing was accomplished by using Coolade as a nonionic and low-foaming surfactant. Coolade-assisted ozonolysis of alkenes in water provided the desired carbonyl products in good yields and comparable to those achieved in organic solvents. During the ozonolysis reaction, water molecules trapped within the polyethylene glycol region of Coolade were proposed to intercept the Criegee intermediate to provide a hydroxy hydroperoxide intermediate. Decomposition of the hydroxy hydroperoxide led to formation of the carbonyl product without the need for a reductant typically required for the conventional ozonolysis using organic solvents. This study presents Coolade as an effective surfactant to improve the solubility of alkenes while mitigating frothing during the ozonolysis in water.
- Buntasana, Supanat,Hayashi, Jun,Klumphu, Piyatida,Padungros, Panuwat,Saetung, Prakorn,Vilaivan, Tirayut
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supporting information
(2022/02/23)
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- AEROBIC ELECTROCATALYTIC OXIDATION OF HYDROCARBONS
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This invention is directed to a method of oxygenating hydrocarbons with molecular oxygen, O2, as oxidant under electrochemical reducing conditions, using polyoxometalate compounds containing copper such as Q10 [Gu4(H2O)2(B-α-PW9O)2] or Q12{ [Cu(H2O)]3[(A-α- PW9O34)2(NO3)-] } or solvates thereof as catalysts, wherein Q are each independently selected from alkali metal cations, alkaline earth metal cations, transition metal cations, NH4+,H+ or any combination thereof.
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Paragraph 0074
(2022/01/04)
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- Effect of relative percentage of acid and base sites on the side-chain alkylation of toluene with methanol
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K3PO4/NaX catalysts were prepared by loading potassium phosphate on NaX zeolite, and the catalytic performance was studied for the side-chain alkylation of toluene with methanol to styrene and ethylbenzene. Combined with the characte
- Li, Huijun,Wang, Bin,Wen, Yueli,Hao, Chunyao,Liu, Yuhua,Huang, Wei
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p. 12703 - 12709
(2021/04/14)
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- Selective Reductive Dimerization of CO2into Glycolaldehyde
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The selective dimerization of CO2 into glycolaldehyde is achieved in a one-pot two-step process via formaldehyde as a key intermediate. The first step concerns the iron-catalyzed selective reduction of CO2 into formaldehyde via formation and controlled hydrolysis of a bis(boryl)acetal compound. The second step concerns the carbene-catalyzed C-C bond formation to afford glycolaldehyde. Both carbon atoms of glycolaldehyde arise from CO2 as proven by the labeling experiment with 13CO2. This hybrid organometallic/organic catalytic system employs mild conditions (1 atm of CO2, 25 to 80 °C in less than 3 h) and low catalytic loadings (1 and 2.5%, respectively). Glycolaldehyde is obtained in 53% overall yield. The appealing reactivity of glycolaldehyde is exemplified (i) in a dimerization process leading to C4 aldose compounds and (ii) in a tri-component Petasis-Borono-Mannich reaction generating C-N and C-C bonds in one process.
- Zhang, Dan,Jarava-Barrera, Carlos,Bontemps, Sébastien
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p. 4568 - 4575
(2021/05/04)
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- Transfer hydrogenation of CO2into formaldehyde from aqueous glycerol heterogeneously catalyzed by Ru bound to LDH
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Aqueous glycerol was used in this study as a liquid-phase hydrogen source for the hydrogenation of CO2. It was found that hydrogen could be efficiently evolved from aqueous glycerol upon highly dispersed Ru on layered double hydroxide (LDH), inducing the transformation of CO2 into formaldehyde under base-free conditions at low temperature.
- Deng, Lidan,Liu, Xiaowei,Xu, Jie,Zhou, Zijian,Feng, Shixiang,Wang, Zheng,Xu, Minghou
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supporting information
p. 5167 - 5170
(2021/05/31)
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- Enhanced CO2 Conversion into Ethanol by Permanently Polarized Hydroxyapatite through C?C Coupling
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Hydroxyapatite (HAp) is a naturally occurring mineral form of calcium apatite of biomedical importance due to its similarity with human hard tissues in morphology and composition. Upon polarization at high temperature, applying 3 kV/cm at 1000 °C, the resulting polarized HAp (p-HAp) exhibits enhanced catalytic behavior due charge accumulation at the interface. More specifically, p-HAp was found to catalyse the conversion of mixtures of CO2(g) and CH4(g) into low carbon organic molecules and into amino acids when N2(g) was added to the mixture. In this work, we report how p-HAp facilitates the conversion of CO2(g) mainly in ethanol by means of forming C?C coupled bonds on its activated surface. After evaluation of a wide range of experimental conditions, we evidence the production of formic acid, methanol and formaldehyde (C1 products); ethanol and acetic acid (C2 products); and acetone (C3 product) from CO2(g) using moderate reaction conditions. Moreover, optimization of the reaction parameters led to a significant increase towards ethanol.
- Sans, Jordi,Sanz, Vanesa,Turon, Pau,Alemán, Carlos
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p. 5025 - 5033
(2021/10/29)
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- PROCESSES FOR PREPARING C-4 SUGARS AND KETOSE SUGARS
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Various processes for preparing C4 aldoses and/or ketones thereof are described. Various processes are described for preparing C4 aldoses and/or ketones thereof from feed compositions comprising glycolaldehyde. Also, various processes for preparing useful downstream products and intermediates, such as erythritol and erythronic acid, from the C4 aldoses and/or ketones thereof are described.
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Page/Page column 19-21; 35-36
(2021/11/20)
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- PROCESSES FOR THE PYROLYSIS OF CARBOHYDRATES
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Various processes for the pyrolysis of carbohydrates to prepare products such as glycolaldehyde are described. Also, various catalysts and processes for preparing catalysts useful for carbohydrate pyrolysis are described.
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Page/Page column 13-15; 27-28
(2021/11/20)
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- Method for preparing aldehyde/ketone by breaking C-C key
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The invention discloses a method for preparing aldehyde/ketone by breaking C-C bonds, and the method comprises the following steps of anaerobic condition. In an organic solvent system, an alcohol is used as a reaction raw material, and the C-C bond is selectively broken under the common action of an iron catalyst, an organic base and an additive to obtain aldehyde/ketone. The method is low in cost, easy to obtain, wide in substrate range, simple and product in post-treatment and high in purity, a new synthetic route and a method are developed for an aldehyde ketone compound, and the method has good application potential and research value.
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Paragraph 0113-0118
(2021/11/19)
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- Lanthanum modified Fe-ZSM-5 zeolites for selective methane oxidation with H2O2
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Selective partial oxidation of methane to methanol under ambient conditions is a great challenge in chemistry. Iron modified ZSM-5 catalysts are shown to be effective for this reaction using H2O2as the oxidant. However, the high consumption of H2O2over this catalyst presents a major disadvantage. Here we report a lanthanum modified Fe-ZSM-5 (LaFe-ZSM-5) catalyst for enhanced selective methane oxidation with suppressed H2O2consumption. Using 0.5 wt% LaFe-ZSM-5 pretreated with H2the productivity of primary oxygenated products (CH3OH, CH3OOH, HCOOH) is 3200 mol kgLaFe?1h?1in 0.1 M H2O2, with a selectivity of 98.9% to primary oxygenated products. The productivity is increased to 11?460 mol kgLaFe?1h?1in 0.5 M H2O2. Compared with Fe-ZSM-5, LaFe-ZSM-5 uses 31% less H2O2for obtaining per mol of product under the same conditions.In situDRIFT spectroscopy and solid state MAS NMR revealed the high H2O2consumption in ZSM-5 based catalyst maybe closely related to the acidity of strong Br?nsted acid sites (Si(OH)Al). The La modified ZSM-5 catalyst can decrease the acidity of the strong Br?nsted acid sites and this suppresses the decomposition of H2O2
- Barnes, Alexandra J.,Bere, Takudzwa,Dummer, Nicholas F.,Gong, Xiaoxiao,Hutchings, Graham J.,Lewis, Richard J.,Morgan, David J.,Richards, Nia,Shaw, Greg,Sun, Songmei
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p. 8052 - 8064
(2021/12/27)
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- CATALYST WITH A CORE-SHELL STRUCTURE FOR METHANE OXIDATION, METHOD OF PREPARING THE SAME AND METHOD OF OXIDIZING METHANE USING THE SAME
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The present invention relates to a catalyst with a core-shell structure for methane oxidation, a method of preparing the same, and a method of methane oxidation using the same, and the catalyst comprises a core structure consisting of a nano-support and core nanoparticles; and a shell coating layer coated on the core structure in which the core nanoparticles have a particle diameter smaller than that of the nano-support and are coated on the nano-support to form a core structure, and it has excellent thermal stability during methane oxidation reaction at high temperature and an effect of increasing methane conversion and formaldehyde selectivity.
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Paragraph 19; 48; 49; 60-63
(2020/05/15)
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- Development of Na2Ti6O13/CuO/Cu2O heterostructures for solar photocatalytic production of low-carbon fuels
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Na2Ti6O13/CuO/Cu2O materials were prepared by solid-state and impregnation method, using copper oxide as cocatalyst (CC, 0.1%–5%). The catalytic activity was evaluated for H2 evolution and CO2 reduction. XPS analysis revealed the presence of Cu2O and CuO in different proportions. Na2Ti6O13 impregnated with 0.1% of cocatalyst exhibits majoritary the Cu2O phase; while Na2Ti6O13 with 5% of cocatalyst shows mainly CuO. Electrochemical measurements showed higher photocurrent and lower resistance to charge transference in Na2Ti6O13-0.1% CC, associated with better a charge flow. Na2Ti6O13-0.1% CC exhibited the highest H2 production (33 μmol g-1 h-1) and Na2Ti6O13-5% CC showed the best CO2 conversion to CH2O (25 μmol g-1 h-1) and CH3OH (4.6 μmol g-1 h-1). A major content of Cu2O phase favored the H2 evolution by the formation of a Z-scheme, where the strong negative character of the CB of Cu2O enhances the kinetics of H2O reduction, while a higher content of CuO improved CO2 adsorption and reduction.
- Ibarra-Rodríguez, Luz I.,Huerta-Flores, Ali M.,Torres-Martínez, Leticia M.
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- Effect of Mo dispersion on the catalytic properties and stability of Mo-Fe catalysts for the partial oxidation of methanol
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Mo-Fe catalysts with different Mo dispersions were synthesized with fast (Cat-FS, 600 r·min?1) or slow stirring speed (Cat-SS, 30 r·min?1) by the coprecipitation method. Improving the stirring speed strengthened the mixing of the solution and increased the dispersion of particles in the catalyst, which exhibited favorable activity and selectivity. The byproduct (dimethyl ether (DME)) selectivity increased from 2.3% to 2.8% with Cat-SS, while it remained unchanged with Cat-FS in a stability test. The aggregation of particles and thin Mo-enriched surface layer decreased the catalyst surface area and slowed down the reoxidation of reduced active sites with Cat-SS, leaving more oxygen vacancies which promoted the formation of DME by the nonoxidative channel.
- Han, Minghan,Zhang, Shuai
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- Preparation and Application of Palladium Nanoparticle Impregnated Chloromethylated Polysulfone Matrix as an Efficient Catalytic Membrane for Oxidation of Alcohols
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The use of palladium nanoparticles embedded in a chloromethylated Polysulfone (CMPSf) matrix was developed for highly efficient oxidation of primary and secondary alcohols to corresponding aldehyde and ketone in organic solvent free condition. Pd (Π)/bis (2, 4-dihydroxybenzaldehyde) chelate chemically incorporated onto CMPSf was used to prepare beneficial catalytic membranes. Chemical structure and thermal properties of resulting membranes were characterized via FTIR, 1HNMR, UV-vis, TGA and DSC techniques. Morphology and particle distribution throughout the catalytic membranes was elucidated using FE-SEM. An average particle size of Pd nanoparticles was estimated about 20 nm by XRD technique. ICP technique proved that no Pd particles were leached out of the membrane into the solutions; hence the as-prepared catalytic membranes could be used several times without significant loss in their activities. This is in good accordance with formation of chemical bond between Pd and polymer matrix.
- Mahdavi, Hossein,Fayyazi, Faeze
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- Epoxidation of Ethylene with Products of Thermal Gas-Phase Oxidation of n-Butane
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Abstract: Epoxidation of ethylene with the reactive products formed during thermal gas-phase oxidation of n-butane has been carried out under flow conditions with the separation of the zones of generation of radicals and their interaction with ethylene. Butane is oxidized in the first section of a two-section reactor, and ethylene is fed to the second section. It has been found that increasing the residence time of a butane–oxygen mixture in the first section of the reactor from 7 to 13 s increases the ethylene oxide accumulation rate. A further increase in the contact time leads to a decrease in the rate. Similarly, increasing the C4H10/O2 ratio in the range of 0.05–0.25 leads to an increase in the rate of accumulation of ethylene oxide. A further increase in this ratio decreases the rate of epoxidation. It has also been found that the temperature dependences of the ethylene oxide accumulation rate in both sections of the reactor pass through a maximum. The obtained data give evidence for the occurrence of the ethylene epoxidation reaction initiated by the n-butane oxidation products under the conditions when ethylene itself is slightly oxidized.
- Arsentev, S. D.,Grigoryan, R. R.
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p. 187 - 193
(2020/03/30)
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- Sustainable acrolein production from bio-alcohols on spinel catalysts: Influence of magnesium substitution by various transition metals (Fe, Zn, Co, Cu, Mn)
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Acrolein is a widely used intermediate of synthesis for value-added compounds in a number of domains of application. This work reports on the sustainable synthesis of acrolein by oxidative coupling of bio-alcohols, which constitutes a very promising alternative to fossil fuel-based production. The synthesis is performed in two sequential reactors, using an iron molybdate catalyst for oxidation and then a magnesium aluminate spinel where magnesium is partly or totally substituted by transition metals (Fe, Zn, Co, Cu, Mn) as a catalyst for cross-aldolization. The acid-base properties of the latter catalysts were determined using SO2 and NH3 adsorption microcalorimetry. Adsorption microcalorimetry was also used to study the adsorption properties of the reactants, with formaldehyde, acetaldehyde and propionaldehyde as probe molecules, and was complemented by a FT-IR investigation of reactant adsorption in order to better understand the mechanisms of adsorption and reaction. Acrolein production was found to be correlated to the ionic radius of the transition metals used in the catalysts, indicating that electronic effects are likely a factor influencing the acrolein production.
- Auroux, Aline,Dubois, Jean-Luc,Folliard, Vincent,Marra, Livia,Postole, Georgeta
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- Bimetallic gold-silver catalysts based on ZnO and Zn/SBA-15 – The effect of various treatments on surface and catalytic properties
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Two different supports containing zinc (ZnO and Zn/SBA-15) were used to prepare mono- and bimetallic gold, silver and gold-silver catalysts. Zinc was used for two different purposes in these materials: (i) as a support in the form of zinc oxide and (ii) as a dopant introduced to short-channel SBA-15 by wetness impregnation. Short channel SBA-15 was used as the reference support. The materials obtained were characterized by: N2 physisorption, XRD, TEM, UV–vis, XPS, XAS and their activity was tested in the reactions of propene and methanol oxidation in the gas phase. The state of metals (Au, Ag, Zn) and the composition of gold-silver alloy formed on the catalysts surface were considered in terms of thermal activation of catalysts in inert gas and in hydrogen flow as well as interaction with reagents and products of methanol and propene oxidation. It was found that silver species were responsible for the activity in propene oxidation and its total combustion to CO2, whereas (Au0)δ? metallic particles were active in methanol oxidation. Selectivity to acrolein in propene oxidation was achieved thanks to the presence of Au-Ag alloy whose composition depended on the presence of zinc oxide and activation conditions. The alloy was not stable and separated into metals upon propene oxidation conditions. In methanol oxidation, zinc species took part in selective oxidation to methyl formate.
- Kaskow, Iveta,Sobczak, Izabela,Yang, Chia-Min,Ziolek, Maria
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p. 110 - 121
(2019/06/24)
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- Singlet oxygen generation by the reaction of acrolein with peroxynitrite via a 2-hydroxyvinyl radical intermediate
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Acrolein (2-propenal) is an environmental pollutant, food contaminant, and endogenous toxic by-product formed in the thermal decomposition and peroxidation of lipids, proteins, and carbohydrates. Like other α,β-unsaturated aldehydes, acrolein undergoes Michael addition of nucleophiles such as basic amino acids residues of proteins and nucleobases, triggering aging associated disorders. Here, we show that acrolein is also a potential target of the potent biological oxidant, nitrosating and nitrating agent peroxynitrite. In vitro studies revealed the occurrence of 1,4-addition of peroxynitrite (k2 = 6 × 103 M?1 s?1, pH 7.2, 25 °C) to acrolein in air-equilibrated phosphate buffer. This is attested by acrolein concentration-dependent oxygen uptake, peroxynitrite consumption, and generation of formaldehyde and glyoxal as final products. These products are predicted to be originated from the Russell termination of ?OOCH=CH(OH) radical which also includes molecular oxygen at the singlet delta state (O2 1Δg). Accordingly, EPR spin trapping studies with the 2,6-nitrosobenzene-4-sulfonate ion (DBNBS) revealed a 6-line spectrum attributable to the 2-hydroxyvinyl radical adduct. Singlet oxygen was identified by its characteristic monomolecular IR emission at 1,270 nm in deuterated buffer, which was expectedly quenched upon addition of water and sodium azide. These data represent the first report on singlet oxygen creation from a vinylperoxyl radical, previously reported for alkyl- and formylperoxyl radicals, and may contribute to better understand the adverse acrolein behavior in vivo.
- Augusto, Ohara,Bechara, Etelvino J. H.,Di Mascio, Paolo,Gon?alves, Leticia C. P.,Klassen, Aline,Licciardi, Saymon,Linares, Edlaine,Massari, Júlio,Prado, Fernanda M.,Tavares, Marina F. M.
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- Photooxidation Reactions of Ethyl 2-Methylpropionate (E2MP) and Ethyl 2,2-Dimethylpropionate (E22DMP) Initiated by OH Radicals: An Experimental and Computational Study
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The relative rate (RR) technique was used for the measurement of OH-initiated photooxidation reactions of ethyl 2-methylpropionate (E2MP) and ethyl 2,2-dimethylpropionate (E22DMP) in the temperature range of 268-363 K at 760 Torr. In addition to this, the
- Kaipara, Revathy,Rajakumar, B.
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p. 2768 - 2784
(2020/05/08)
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- Synthesis of High Dimensionally Structured Mo-Fe Mixed Metal Oxide and Its Catalytic Activity for Selective Oxidation of Methanol
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High-dimensionally structured Mo-Fe oxide (HDS-MoFeO) was synthesized through an assembly of structural units supplied from Keplerate-type polyoxometalate, {Mo72Fe30}, under an appropriate hydrothermal condition. HDS-MoFeO showed excellent catalytic activity for the selective oxidation of methanol with slightly lower selectivity for formaldehyde than that of a conventional Mo-Fe oxide catalyst.
- Hiyoshi, Norihito,Ishikawa, Satoshi,Kumaki, Masahiro,Shimoda, Kosuke,Tashiro, Masaya,Ueda, Wataru
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supporting information
(2020/04/15)
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- Visible-light-induced C-C bond cleavage of lignin model compounds with cyanobenziodoxolone
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The catalytic degradation of lignin to value-added chemicals has received considerable attention over the past decade. Photocatalysis provides promising approaches to enable previously inaccessible transformations. However, examples of the visible-light promoted degradation of lignin are still limited. In this work, the visible-light-induced selective C-C bond cleavage of β-O-4 lignin model compounds has been disclosed via β-scission of in situ generated alkoxy radical intermediates. With cyanobenziodoxolone as the oxidant, a variety of substrates could be transformed into aldehydes in moderate to good yields. In addition, unexpected acetal esters which could conveniently furnish formaldehyde and phenols by alcoholysis were observed.
- Zheng, Ming,Huang, Yan,Zhan, Le-Wu,Hou, Jing,Li, Bin-Dong
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- The influence of H/D kinetic isotope effect on radiation-induced transformations of hydroxyl-containing compounds in aqueous solutions
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Vicinal diols and its derivatives can be exploited as model compounds for the investigation of radiation-induced free-radical transformations of hydroxyl-containing biomolecules such as carbohydrates, phospholipids, ribonucleotides, amino acids, and peptides. In this paper, for the first time, the prospects of isotope reinforcement approach in inhibiting free-radical transformations of hydroxyl-containing compounds in aqueous solutions are investigated on the example of radiolysis of 1,2-propanediol and 1,2-propanediol-2-d1 aqueous solutions. At an absorbed dose rate of 0.110 ± 0.003 Gy·s?1 a profound kinetic isotope effect (KIE) is observed for the non-branched chain formation of acetone, which is a final dehydration product of predominant carbon-centred radicals CH3·C(OH)CH2OH. In 0.1 and 1 M deaerated solutions at pH 7.00 ± 0.01, the values of KIE are 8.9 ± 1.7 and 15.3 ± 3.1, respectively. A rationale for the fact that a strong KIE takes place only in the case of chain processes, which may occur during free-radical transformations of vicinal diols, is also provided herein based on the results of 2-propanol and 2-propanol-2-d1 indirect radiolysis. Lastly, the lack of KIE is shown in the case of 2-butanone formation from 2,3-butanediol or 2,3-butanediol-2,3-d2. This indicates that the type (primary, secondary) of the β-carbonyl radicals formed as a result of CH3·C(OH)CH(OH)R (R = H, CH3) dehydration determines the manifestation of the effect.
- Bekish, Andrei V.,Nepachalovich, Palina S.,Shadyro, Oleg I.,Shmanai, Vadim V.
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p. 732 - 744
(2020/12/28)
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- Insights into Redox Dynamics of Vanadium Species Impregnated in Layered Siliceous Zeolitic Structures during Methanol Oxidation Reactions
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Supported transition metal catalysts have been extensively applied to oxidative and reductive processes. The understanding of surface speciation and active site-support interactions in these materials play a substantial role in developing improved heterogeneous catalysts. Herein, a series of impregnated 3D ferrierite and 2D ITQ-6 siliceous supports with variable loading of vanadium oxide was prepared. Chemical and structural properties of the materials were studied by X-ray diffraction, N2 physisorption, inductively coupled plasma – optical emission spectrometry, X-ray absorption, Fourier transform infrared and diffuse reflectance UV-vis spectroscopies, and temperature-programmed reduction with H2. Reactivity of the catalyst surface, associated with the incidence of isolated silanol groups, was found to be more effective when vanadium oxides were better dispersed and stabilized than increases in surface area. Differences in activation and the oxidation state dynamic behavior of active sites were then probed by methanol oxidation as a model reaction monitored by in situ FTIR spectroscopy and XANES/MS. By applying isothermal periods of reaction under non-oxidizing atmosphere and regeneration of catalysts by O2, it was found that, even at distinct rates, all types of sites are accessible during reaction, since a complete reduction to V4+ was observed. However, reoxidation of sites to V5+ is limited and sensitive to the different vanadium species on the surface, and probably, the determinant factor of the distinct V5+/V4+ equilibrium reached for the catalysts when the reaction is carried out under constant oxidizing atmosphere.
- Vieira, Luiz H.,Possato, Luiz G.,Chaves, Thiago F.,Lee, Jason J.,Sulmonetti, Taylor P.,Jones, Christopher W.,Martins, Leandro
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p. 141 - 151
(2019/11/13)
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- Reductive Electrochemical Activation of Molecular Oxygen Catalyzed by an Iron-Tungstate Oxide Capsule: Reactivity Studies Consistent with Compound i Type Oxidants
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The reductive activation of molecular oxygen catalyzed by iron-based enzymes toward its use as an oxygen donor is paradigmatic for oxygen transfer reactions in nature. Mechanistic studies on these enzymes and related biomimetic coordination compounds designed to form reactive intermediates, almost invariably using various "shunt" pathways, have shown that high-valent Fe(V)=O and the formally isoelectronic Fe(IV) =O porphyrin cation radical intermediates are often thought to be the active species in alkane and arene hydroxylation and alkene epoxidation reactions. Although this four decade long research effort has yielded a massive amount of spectroscopic data, reactivity studies, and a detailed, but still incomplete, mechanistic understanding, the actual reductive activation of molecular oxygen coupled with efficient catalytic transformations has rarely been experimentally studied. Recently, we found that a completely inorganic iron-tungsten oxide capsule with a keplerate structure, noted as {Fe30W72}, is an effective electrocatalyst for the cathodic activation of molecular oxygen in water leading to the oxidation of light alkanes and alkenes. The present report deals with extensive reactivity studies of these {Fe30W72} electrocatalytic reactions showing (1) arene hydroxylation including kinetic isotope effects and migration of the ipso substituent to the adjacent carbon atom ("NIH shift"); (2) a high kinetic isotope effect for alkyl C - H bond activation; (3) dealkylation of alkylamines and alkylsulfides; (4) desaturation reactions; (5) retention of stereochemistry in cis-alkene epoxidation; and (6) unusual regioselectivity in the oxidation of cyclic and acyclic ketones, alcohols, and carboxylic acids where reactivity is not correlated to the bond disassociation energy; the regioselectivity obtained is attributable to polar effects and/or entropic contributions. Collectively these results also support the conclusion that the active intermediate species formed in the catalytic cycle is consistent with a compound I type oxidant. The activity of {Fe30W72} in cathodic aerobic oxidation reactions shows it to be an inorganic functional analogue of iron-based monooxygenases.
- Bugnola, Marco,Shen, Kaiji,Haviv, Eynat,Neumann, Ronny
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p. 4227 - 4237
(2020/05/05)
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- Bioinspired Oxidation of Methane in the Confined Spaces of Molecular Cages
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Non-heme iron, vanadium, and copper complexes bearing hemicryptophane cavities were evaluated in the oxidation of methane in water by hydrogen peroxide. According to 1H nuclear magnetic resonance studies, a hydrophobic hemicryptophane cage accommodates a methane molecule in the proximity of the oxidizing site, leading to an improvement in the efficiency and selectivity for CH3OH and CH3OOH compared to those of the analogous complexes devoid of a hemicryptophane cage. While copper complexes showed low catalytic efficiency, their vanadium and iron counterparts exhibited higher turnover numbers, ≤13.2 and ≤9.2, respectively, providing target primary oxidation products (CH3OH and CH3OOH) as well as over-oxidation products (HCHO and HCOOH). In the case of caged vanadium complexes, the confinement effect was found to improve either the selectivity for CH3OH and CH3OOH (≤15%) or the catalytic efficiency. The confined space of the hydrophobic pocket of iron-based supramolecular complexes plays a significant role in the improvement of both the selectivity (≤27% for CH3OH and CH3OOH) and the turnover number of methane oxidation. These results indicate that the supramolecular approach is a promising strategy for the development of efficient and selective bioinspired catalysts for the mild oxidation of methane to methanol.
- Ikbal, Sk Asif,Colomban, Cédric,Zhang, Dawei,Delecluse, Magalie,Brotin, Thierry,Dufaud, Véronique,Dutasta, Jean-Pierre,Sorokin, Alexander B.,Martinez, Alexandre
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supporting information
p. V
(2019/06/10)
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- Photocatalytic CO2 Conversion of M0.33WO3 Directly from the Air with High Selectivity: Insight into Full Spectrum-Induced Reaction Mechanism
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Natural photosynthesis is a solar light-driven process utilized by plants to convert CO2 and water into carbohydrate molecules. The goal of artificial photosynthesis is the reduction of CO2 directly from air into high purity value-added products at atmospheric pressure. However, its realization, combined with deep mechanism investigation, is a huge challenge. Herein, we demonstrate that hexagonal tungsten bronze M0.33WO3 (M = K, Rb, Cs) series with {010} facets, prepared by a peculiar "water-controllable releasing" solvothermal method, showed excellent full spectrum (UV, visible, and NIR lights)-induced photocatalytic CO2 reduction performance directly from the air at ambient pressure. Particularly, after 4 h near-infrared light irradiation, ca. 4.32% CO2 in the air could be converted into CH3OH with 98.35% selectivity for Rb0.33WO3. The experiments and theoretical calculations unveiled that the introduced alkali metal atom occupied the tunnel of hexagonal structure and donated more free electrons to reconstruct the electronic structure of M0.33WO3, which can enhance the polaron transition, modify the energy band structure, selectively adsorb CO2 rather than O2 from the air, decrease the activation energy of CO2 reaction, and finally make the effective CO2 reduction in the air a reality. This work may provide a new possibility for the practical application of artificial photosynthesis.
- Wu, Xiaoyong,Li, Yuan,Zhang, Gaoke,Chen, Hong,Li, Jun,Wang, Kai,Pan, Yang,Zhao, Yan,Sun, Yongfu,Xie, Yi
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supporting information
p. 5267 - 5274
(2019/03/26)
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- Cerium oxide nanoparticles as catalyst for the oxidation of methanol
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This study outlines the synthesis of cerium oxide nanoparticles, their characterization and their activity in the oxidation of methanol. A simple and easy co-precipitation method was used for the preparation of cerium oxide, without any added surfactants. The physicochemical properties of the sample were studied using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD).The morphology and size of the catalyst was studied using SEM.EDX confirms the element content of the synthesized cerium oxide.The structure of CeO2 was confirmed using XRD. Thus, the reported CeO2 was an active catalyst for methanol oxidation to form formaldehyde at a temperature range of 523–753K in the gas phase. At 753K, the cerium oxide catalyst gave 53% formaldehyde selectivity, 57% methanol conversion and 31% formaldehyde yields.
- Bayahia, Hossein
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p. 1539 - 1545
(2019/12/11)
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- Propylene glycol oxidation with hydrogen peroxide over Zr-containing metal-organic framework UiO-66
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Zirconium-based metal–organic framework UiO-66 catalyzes oxidation of propylene glycol (PG) using hydrogen peroxide as green oxidant. Hydroxyacetone (HA) is the main oxidation product, while the main side product is acetic acid (AcA). The nature of the solvent drastically affects PG adsorption, oxidant utilization efficiency and product yields. The best catalytic performance (85% selectivity towards HA at ca. 10% PG conversion) was achieved with water–acetonitrile (3/7 (v/v)) mixture as a solvent. Additives of radical chain scavengers produce a rate-inhibiting effect, suggesting radical chain mechanism of the oxidation process. The PG oxidation over UiO-66 proceeds without leaching of the active metal into solution, and the catalysis has a truly heterogeneous nature. The catalyst can be recycled without significant loss of activity and selectivity and retains its structure during at least five reuses.
- Torbina, Viktoriia V.,Nedoseykina, Nadezhda S.,Ivanchikova, Irina D.,Kholdeeva, Oxana A.,Vodyankina, Olga V.
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- Halogen Substitution Influences Ketamine Metabolism by Cytochrome P450 2B6: In Vitro and Computational Approaches
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Ketamine is analgesic at anesthetic and subanesthetic doses, and it has been used recently to treat depression. Biotransformation mediates ketamine effects, influencing both systemic elimination and bioactivation. CYP2B6 is the major catalyst of hepatic ketamine N-demethylation and metabolism at clinically relevant concentrations. Numerous CYP2B6 substrates contain halogens. CYP2B6 readily forms halogen-protein (particularly Cl-π) bonds, which influence substrate selectivity and active site orientation. Ketamine is chlorinated, but little is known about the metabolism of halogenated analogs. This investigation evaluated halogen substitution effects on CYP2B6-catalyzed ketamine analogs N-demethylation in vitro and modeled interactions with CYP2B6 using various computational approaches. Ortho phenyl ring halogen substituent changes caused substantial (18-fold) differences in Km, on the order of Br (bromoketamine, 10 μM) max varied minimally (83-103 pmol/min/pmol CYP). Thus, apparent substrate binding affinity was the major consequence of halogen substitution and the major determinant of N-demethylation. Docking poses of ketamine and analogs were similar, sharing a π-stack with F297. Libdock scores were deschloroketamine m model generated with Assay Central had a ROC of 0.86. The probability of activity at 15 μM for ketamine and analogs was predicted with this model. Deschloroketamine scores corresponded to the experimental Km, but the model was unable to predict activity with fluoroketamine. The binding pocket of CYP2B6 also suggested a hydrophobic component to substrate docking, on the basis of a strong linear correlation (R2 = 0.92) between lipophilicity (AlogP) and metabolism (log Km) of ketamine and analogs. This property may be the simplest design criteria to use when considering similar compounds and CYP2B6 affinity.
- Wang, Pan-Fen,Neiner, Alicia,Lane, Thomas R.,Zorn, Kimberley M.,Ekins, Sean,Kharasch, Evan D.
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p. 898 - 906
(2019/01/21)
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- Production and testing of technical catalysts based on MnO2 for the abatement of aromatic volatile compounds at the laboratory and pilot plant scales
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Shaping is a crucial step to produce technical catalysts that remains as some sort of dark art for catalytic researchers in academia. This contribution discusses aspects concerning the fabrication of technical catalysts based on MnO2 powders ai
- Baldovino-Medrano, Víctor Gabriel,Kartheuser, Beno?t,Gaigneaux, Eric M.
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- CYP2C19 and 3A4 Dominate Metabolic Clearance and Bioactivation of Terbinafine Based on Computational and Experimental Approaches
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Lamisil (terbinafine) is an effective, widely prescribed antifungal drug that causes rare idiosyncratic hepatotoxicity. The proposed toxic mechanism involves a reactive metabolite, 6,6-dimethyl-2-hepten-4-ynal (TBF-A), formed through three N-dealkylation pathways. We were the first to characterize them using in vitro studies with human liver microsomes and modeling approaches, yet knowledge of the individual enzymes catalyzing reactions remained unknown. Herein, we employed experimental and computational tools to assess terbinafine metabolism by specific cytochrome P450 isozymes. In vitro inhibitor phenotyping studies revealed six isozymes were involved in one or more N-dealkylation pathways. CYP2C19 and 3A4 contributed to all pathways, and so, we targeted them for steady-state analyses with recombinant isozymes. N-Dealkylation yielding TBF-A directly was catalyzed by CYP2C19 and 3A4 similarly. Nevertheless, CYP2C19 was more efficient than CYP3A4 at N-demethylation and other steps leading to TBF-A. Unlike microsomal reactions, N-denaphthylation was surprisingly efficient for CYP2C19 and 3A4, which was validated by controls. CYP2C19 was the most efficient among all reactions. Nonetheless, CYP3A4 was more selective at steps leading to TBF-A, making it more effective in terbinafine bioactivation based on metabolic split ratios for competing pathways. Model predictions did not extrapolate to quantitative kinetic constants, yet some results for CYP3A4 and CYP2C19 agreed qualitatively with preferred reaction steps and pathways. Clinical data on drug interactions support the CYP3A4 role in terbinafine metabolism, while CYP2C19 remains understudied. Taken together, knowledge of P450s responsible for terbinafine metabolism and TBF-A formation provides a foundation for investigating and mitigating the impact of P450 variations in toxic risks posed to patients.
- Davis, Mary A.,Barnette, Dustyn A.,Flynn, Noah R.,Pidugu, Anirudh S.,Swamidass, S. Joshua,Boysen, Gunnar,Miller, Grover P.
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p. 1151 - 1164
(2019/05/01)
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- Formation of Glyoxylic Acid in Interstellar Ices: A Key Entry Point for Prebiotic Chemistry
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With nearly 200 molecules detected in interstellar and circumstellar environments, the identification of the biologically relevant α-keto carboxylic acid, glyoxylic acid (HCOCOOH), is still elusive. Herein, the formation of glyoxylic acid via cosmic-ray driven, non-equilibrium chemistry in polar interstellar ices of carbon monoxide (CO) and water (H2O) at 5 K via barrierless recombination of formyl (HCO) and hydroxycarbonyl radicals (HOCO) is reported. In temperature-programmed desorption experiments, the subliming neutral molecules were selectively photoionized and identified based on the ionization energy and distinct mass-to-charge ratios in combination with isotopically labeled experiments exploiting reflectron time-of-flight mass spectrometry. These studies unravel a key reaction path to glyoxylic acid, an organic molecule formed in interstellar ices before subliming in star-forming regions like SgrB2(N), thus providing a critical entry point to prebiotic organic synthesis.
- Eckhardt, André K.,Bergantini, Alexandre,Singh, Santosh K.,Schreiner, Peter R.,Kaiser, Ralf I.
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supporting information
p. 5663 - 5667
(2019/03/29)
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- CATALYSTS COMPRISING SILICON MODIFIED NICKEL
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Nickel-based catalysts comprising silicon modified nickel (nickel silicate) are provided, as are methods for using the catalysts to i) convert methane to CO and H2 (e.g. for use in synthetic chemical compound production); or to ii) convert methane to oxygenated hydrocarbons e.g. one or more of methanol, acetone, formaldehyde, and dimethyl ether. The catalysts are bifunctional and comprise both Ni metallic catalytic sites and acidic nickel-silicon catalytic sites, and the conversions are performed under moderate reaction conditions.
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Paragraph 0110
(2019/09/20)
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- Probing the Reaction Mechanisms Involved in the Decomposition of Solid 1,3,5-Trinitro-1,3,5-triazinane by Energetic Electrons
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The decomposition mechanisms of 1,3,5-trinitro-1,3,5-triazinane (RDX) have been explored over the past decades, but as of now, a complete picture on these pathways has not yet emerged, as evident from the discrepancies in proposed reaction mechanisms and the critical lack of products and intermediates observed experimentally. This study exploited a surface science machine to investigate the decomposition of solid-phase RDX by energetic electrons at a temperature of 5 K. The products formed during irradiation were monitored online and in situ via infrared and UV-vis spectroscopy, and products subliming in the temperature programmed desorption phase were probed with a reflectron time-of-flight mass spectrometer coupled with soft photoionization at 10.49 eV (ReTOF-MS-PI). Infrared spectroscopy revealed the formation of water (H2O), carbon dioxide (CO2), dinitrogen oxide (N2O), nitrogen monoxide (NO), formaldehyde (H2CO), nitrous acid (HONO), and nitrogen dioxide (NO2). ReTOF-MS-PI identified 38 cyclic and acyclic products arranged into, for example, dinitro, mononitro, mononitroso, nitro-nitroso, and amines species. Among these molecules, 21 products such as N-methylnitrous amide (CH4N2O), 1,3,5-triazinane (C3H9N3), and N-(aminomethyl)methanediamine (C2H9N3) were detected for the first time in laboratory experiments; mechanisms based on the gas phase and condensed phase calculations were exploited to rationalize the formation of the observed products. The present studies reveal a rich, unprecedented chemistry in the condensed phase decomposition of RDX, which is significantly more complex than the unimolecular gas phase decomposition of RDX, thus leading us closer to an understanding of the decomposition chemistry of nitramine-based explosives.
- Singh, Santosh K.,Zhu, Cheng,Vuppuluri, Vasant,Son, Steven F.,Kaiser, Ralf I.
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p. 9479 - 9497
(2019/11/11)
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- Influence of Phase Composition of Bulk Tungsten Vanadium Oxides on the Aerobic Transformation of Methanol and Glycerol
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A series of W–V–O catalysts with different m-WO3 and h-WO3 phase contents were hydrothermally synthesized by employing different tungsten, vanadium, and ammonium precursors and characterized by powder XRD, N2 adsorption, SEM, X-ray energy-dispersive spectroscopy, thermogravimetric analysis, Raman and FTIR spectroscopy, NH3 temperature programmed desorption, H2 temperature-programmed reduction, and XPS. Finally, the acid/redox properties were analyzed by using aerobic transformation of methanol as a characterization reaction. A correlation between phase composition as well as acid and redox properties was observed, which were correlated to the catalytic performance of the title materials in a one-pot oxydehydration reaction of glycerol. The hexagonal tungsten bronze (h-WO3) phase shows a significantly higher concentration of acid sites than monoclinic m-WO3, so that the acid properties of W–V–O oxides are directly related to the presence of h-WO3 crystals. The presence of a higher concentration of acid sites in V-containing h-WO3 crystals is a key factor to achieve high selectivity to both acrolein and acrylic acid during one-pot glycerol oxydehydration. Also, V sites in h-WO3 show higher selectivity in the consecutive reaction (partial oxidation of acrolein to acrylic acid), while V sites in the m-WO3 phase fundamentally lead to the formation of carbon oxides.
- Delgado, Daniel,Chieregato, Alessandro,Soriano, M. Dolores,Rodríguez-Aguado, Elena,Ruiz-Rodríguez, Lidia,Rodríguez-Castellón, Enrique,López Nieto, José M.
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p. 1204 - 1211
(2018/03/22)
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- A Highly Stable Copper-Based Catalyst for Clarifying the Catalytic Roles of Cu0 and Cu+ Species in Methanol Dehydrogenation
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Identification of the active copper species, and further illustration of the catalytic mechanism of Cu-based catalysts is still a challenge because of the mobility and evolution of Cu0 and Cu+ species in the reaction process. Thus, an unprecedentedly stable Cu-based catalyst was prepared by uniformly embedding Cu nanoparticles in a mesoporous silica shell allowing clarification of the catalytic roles of Cu0 and Cu+ in the dehydrogenation of methanol to methyl formate by combining isotope-labeling experiment, in situ spectroscopy, and DFT calculations. It is shown that Cu0 sites promote the cleavage of the O?H bond in methanol and of the C?H bond in the reaction intermediates CH3O and H2COOCH3 which is formed from CH3O and HCHO, whereas Cu+ sites cause rapid decomposition of formaldehyde generated on the Cu0 sites into CO and H2.
- Yang, Huanhuan,Chen, Yanyan,Cui, Xiaojing,Wang, Guofu,Cen, Youliang,Deng, Tiansheng,Yan, Wenjun,Gao, Jie,Zhu, Shanhui,Olsbye, Unni,Wang, Jianguo,Fan, Weibin
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supporting information
p. 1836 - 1840
(2018/01/27)
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- Accessing the Nitromethane (CH3NO2) Potential Energy Surface in Methanol (CH3OH)-Nitrogen Monoxide (NO) Ices Exposed to Ionizing Radiation: An FTIR and PI-ReTOF-MS Investigation
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(D3-)Methanol-nitrogen monoxide (CH3OH/CD3OH-NO) ices were exposed to ionizing radiation to facilitate the eventual determination of the CH3NO2 potential energy surface (PES) in the condensed phase. R
- Góbi, Sándor,Crandall, Parker B.,Maksyutenko, Pavlo,F?rstel, Marko,Kaiser, Ralf I.
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p. 2329 - 2343
(2018/03/21)
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- H2 photo-production from methanol, ethanol and 2-propanol: Pt-(Nb)TiO2 performance under UV and visible light
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In this work we analyzed the photo-production of hydrogen using titania-based systems able to profit from UV and visible light photons. For this purpose, we prepared Niobium-doped titania and a titania reference by a microemulsion method, subjected these oxide precursors to calcination and subsequently introduced Pt as co-catalyst by a chemical reduction method. These materials were characterized in terms of the structural and morphological properties of the oxide and metal phases. Using these materials, we measured the reaction rate and quantum efficiency of the hydrogen photo-production using methanol, ethanol, and 2-propanol as sacrificial agents. Significant activity enhancement was observed in the Niobium-doped material with respect to the titania reference material. The study focuses on interpreting the differences presented (between the two samples) among the three alcohols in the hydrogen yield and provides a physico-chemical study to understand the roots of the activity. Such study was mainly based on the analysis of the reaction mechanism using in-situ infrared spectroscopy together with the analysis of the energetics of the reaction taking into account the fate of the sacrificial alcohol during reaction.
- Fontelles-Carceller, Olga,Mu?oz-Batista, Mario J.,Conesa, José Carlos,Kubacka, Anna,Fernández-García, Marcos
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- Conversion of aliphatic C1–C2 alcohols on In– Nb– Mo-doped complex lithium phosphates and HZr2(PO4)3 with NASICON-type structure
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In– Nb– Mo-doped lithium complex phosphates and HZr2(PO4)3 with NASICON-type structure were synthesized in this paper. Particle size distribution lies between 50 and 300 nm. The obtained samples were characterized by X-ray diffraction analysis, scanning electron microscopy and X-ray microanalysis. Investigation of the catalytic properties of synthesized compounds in the C1–C2 alcohols conversions showed that heterovalent doping has a determining effect on the obtained catalysts’ activity and selectivity. It is shown that the thermodynamic factors and the dopant ability to change the degree of oxidation and acid function of the catalysts play a key role in methanol and ethanol conversion. A number of catalysts show the high activity and selectivity of the formation of dimethyl and diethyl ethers and ethylene. High selectivity for C4 hydrocarbons is achieved by LiZr2(PO4)3 and Li0.5Zr2P2.5Mo0.5O12 catalysts (64 and 49%, respectively) in the case of ethanol conversion.
- Ilin,Ermilova,Orekhova,Cretin,Yaroslavtsev
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p. 583 - 590
(2018/03/26)
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- PRODUCTION OF GLYCOLALDEHYDE BY THERMOLYTIC FRAGMENTATION
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The present invention relates to a process for the production of glycolaldehyde by thermolytic fragmentation of a carbohydrate feedstock comprising mono- and/or di-saccharide(s) and a system suitable for performing the process. The process and the system are suitable for industrial application, and the process may be performed in a continuous process.
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Page/Page column 19-10
(2018/06/30)
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