- Supramolecular origins of product selectivity for methanol-to-olefin catalysis on HSAPO-34
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Ethylene selectivity in methanol-to-olefin (MTO) catalysis is related to the number of methyl groups on benzene rings trapped in the nanocages of the preferred catalyst HSAPO-34. By correlating the time evolutions of the catalysts' 13C NMR spectra and the volatile product distribution following abrupt cessation of methanol flow, we discovered that (in the absence of other adsorbates) propene is favored by methylbenzenes with four to six methyl groups but ethylene is predominant from those with two or three methyl groups. We substantially increased ethylene selectivity by operating at lower methanol partial pressures or higher temperatures, either of which reduces the steady-state average methyl substitution. As a step toward a kinetic analysis of the MTO reaction on HSAPO-34, we treated each nanocage with a methylbenzene molecule as a supramolecule capable of unimolecular dissociation into ethylene or propene and a less highly substituted methylbenzene. Addition of a water molecule to a nanocage containing a methylbenzene produces a distinct supramolecule with unique properties. Indeed, co-feeding water with methanol significantly increased the average number of methyl groups per ring at steady state relative to identical conditions without additional water, and also increased ethylene selectivity, apparently through transition state shape selectivity.
- Song,Fu,Haw
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- Amination of butenes over protonic zeolites
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The reaction of 1-butene and isobutene with ammonia has been investigated, far from thermodynamic equilibrium, in the pressure range 1-6 MPa over a series of acidic zeolites. The kinetics are compatible with a Langmuir-Hinshelwood mechanism involving adsorbed species. The rates of amination increase with the Si/Al ratio of the solid. A small influence of the zeolite structure is noticed on the relative adsorption coefficients in the case of 1-butene but not in that of isobutene. The catalytic activity calculated per proton is higher on MFI than on BEA or HY zeolites, but this effect of the structure is less than an order of magnitude. Under the conditions of reaction used in this work large pore zeolites show a good resistance to deactivation. It is proposed that deactivation is mainly due to the formation of strongly basic polyalkylamines and not to coke.
- Lequitte,Figueras,Moreau,Hub
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- The Gas-Phase Elimination Kinetics of 2-Hydroxy-2-Methylbutyric Acid and 2-Ethyl-2-Hydroxybutyric Acid
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The elimination kinetics of the title compounds have been examined over the temperature range of 270 - 320 deg C and pressure range of 19 - 117 torr.The reactions, carried out in seasoned vessels, with the free-radical suppressor toluene always present, are homogeneous, unimolecular, and follow a first-order rate law.The products of 2-hydroxy-2-methylbutyric acid are 2-butanone, CO, and H2O; while of 2-ethyl-2-hydroxybutyric acid are 3-pentanone, CO, and H2O.The rate coeffcient is expressed by the following Arrhenius equation: for 2-hydroxy-2-methylbutyric acid, log k1(s-1) = (12.87 +/- 0.19) - (171.2 +/- 2.1) kJ mol-1 (2.303 RT)-1; and for 2-ethyl-2-hydroxybutyric acid, log k1(s-1) = (12.13 +/- 0.34) - (159.4 +/- 3.7) kJ mol-1 (2.303 RT)-1.Augmentation of alkyl bulkiness at the 2-position of the 2-hydroxycarboxylic acids showed an increase in the rate of dehydration.The electron release of alkyl groups, rather than steric acceleration, appears to enhance the pyrolysis decomposition of these substrates.These reactions are believed to proceed through a semi-polar five-membered cyclic transition type of mechanism.
- Chuchani, Gabriel,Martin, Ignacio,Rotinov, Alexandra
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- Highly Selective MTO Reaction over a Nanosized ZSM-5 Zeolite Modified by Fe via the Low-Temperature Dielectric Barrier Discharge Plasma Method
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Nanosized ZSM-5 zeolites were synthesized via in situ seed-induced hydrothermal method, and samples modified with an Fe promoter were prepared by the traditional wet impregnation-thermal decomposition and dielectric barrier discharge plasma (DBD) methods, respectively. The catalytic performance was studied by the methanol-to-olefin (MTO) reaction. The results showed that the acidity of the catalysts, the dispersity of the Fe promoter, and the interaction degree with the ZSM-5 zeolite are closely related to product selectivity in the MTO reaction. Compared with the Fe-NZ5 sample prepared by the traditional impregnation-calcination method, the FeD-NZ5 samples prepared by the DBD method demonstrated the higher selectivity of C2—C4 light olefins and the lower coke deposition during long-term evaluation (100 hr), which can be attributed to the weaker acid strength, more uniform Fe promoter dispersion, and strong interaction with the ZSM-5 zeolite.
- Bai, Xuefeng,Bukina, Z. M.,Kolesnichenko, N. V.,Li, Yuzong,Maximov, A. L.,Su, Xiaofang,Wang, Wei,Wang, Yongchao,Wu, Wei
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- Oxygen scrambling and stereochemistry during the trifluoroethanolysis of optically active 2-butyl 4-bromobenzenesulfonate
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It is shown that during the trifluoroethanolysis of 2-butyl 4-bromobenzenesulfonate, containing 18O in the nonbridging oxygens, scrambling of the oxygen label occurs. When enantiomerically enriched 2-butyl 4-bromobenzenesulfonate is subjected to the same solvolysis conditions, racemization of the starting ester is not observed. Therefore if an ion-pair intermediate is involved in the trifluoroethanolysis reaction, the ion pair has a sufficient lifetime to permit rotation of the anion leading to oxygen scrambling. However, rotation of the cation, which would lead to racemization, does not occur. The possibility that the oxygen scrambling may be a concerted reaction and not involve an ion-pair intermediate is discussed.
- Dietze, Paul E.,Wojciechowski, Marek
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- TRANSFORMATION OF 1-BUTENE OVER SYNTHETIC ZEOLITES
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The behaviour of several zeolites as catalysts for the title reaction has been investigated by means of a continuous flow microreactor.Runs performed at atmospheric pressure indicated that at 423 K the completely protonic forms of the zeolites catalyze just the isomerization reaction.In the case of Y zeolites, oligomerization occures only over the partially decationated samples, in the temperature range between 373 and 423 K and W/F between 0.2 and 22 gcath/g1-but, to an extent which depends on the reaction conditions.Most of the catalysts were tested also under pressure (4.05 MPa) at 423 K.The protonic forms of Y and ZSM-5 zeolites seem promising catalysts in terms of both conversion and selectivity to oligomers.The 1-olefins account for 30percent of the entire olefinic mixture.The octenes, which account for 70percent of the liquid mixture, are mostly formed of dimethylhexenes.Trimers are also formed during the reaction and, in the very particular case of HZSM-5, tetramers are produced.
- Ferino, Italo,Monaci, Roberto,Solinas, Vincenzo,Forni, Lucio,Rivoldini, Antonio,Sanseverino, Luigi
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- Thermal Decomposition of Allylic Sulfinic Acids: Confirmation of a Retro-ene Mechanism
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The acidolysis of trialkyltin allylic sulfinates yields the corresponding sulfinic acids which undergo a first-order thermal decomposition with γ-syn substitution as predicted for a retro-ene mechanism.
- King, Malcolm D.,Sue, Rodney E.,White, Rodney H.,Young, David J.
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- INFLUENCE OF ETHYLENE ON THE HYDROGENATION OF CO OVER RUTHENIUM
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The interactions of C2H4 with H2 and CO were investigated over a SiO2-supported Ru catalyst.To differentiate carbon sources, 13C-labeled CO and unlabeled C2H4 were used.Product analysis was carried out by isotope-ratio gas chromatography/mass spectrometry.In the absence of CO, C2H4 undergoes extensive hydrogenation.Small amounts of CH4 and C3+ olefins and paraffins are also observed, indicative of C2H4 hydrogenolysis and homologation.The presence of CO strongly suppresses C2H4 hydrogenolysis, but enhances C2H4 homologation.The hydrogenation of CO hydrocarbons is strongly influenced by the presence of C2H4.With increasing C2H4 partial pressure, the hydrogenation of CO to hydrocarbons is progressively suppressed, but the hydroformylation of C2H4 to form propanal (and some 1-propanol) is enhanced.The product distributions observed for the reactions of C2H4 and H2, and C2H4, CO, and H2, can be described in terms of a chain growth mechanism involving C1 and C2 monomer units.
- Jordan, Deborah S.,Bell, Alexis T.
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- Olefin oligomerization via new and efficient Br?nsted acidic ionic liquid catalyst systems
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Olefin oligomerization reaction catalyzed by new catalyst systems (a Br?nsted-acidic ionic liquid as the main catalyst and tricaprylylmethylammonium chloride as the co-catalyst) has been investigated. The synthesized Br?nsted acidic ionic liquids were characterized by Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV), 1H nuclear magnetic resonance (NMR), and 13C NMR to analyze their structures and acidities. The influence of different ionic liquids, ionic liquid loading, different co-catalysts, catalyst ratios (mole ratio of ionic liquid to co-catalyst), reaction time, pressure, temperature, solvent, source of reactants, and the recycling of catalyst systems was studied. Among the synthesized ionic liquids, 1-(4-sulfonic acid)butyl-3-hexylimidazolium hydrogen sulfate ([HIMBs]HSO4) exhibited the best catalytic activity under the tested reaction conditions. The conversion of isobutene and selectivity of trimers were 83.21% and 35.80%, respectively, at the optimum reaction conditions. Furthermore, the catalyst system can be easily separated and reused; a feasible reaction mechanism is proposed on the basis of the distribution of experimental products.
- Wang, Guoqin,Song, Heyuan,Li, Ruiyun,Li, Zhen,Chen, Jing
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- Kinetics and mechanism of the homogeneous oxidation of n-butenes to methyl ethyl ketone in a solution of mo-v-phosphoric heteropoly acid in the presence of palladium pyridine-2,6-dicarboxylate
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In catalytic two-step n-butene oxidation with dioxygen to methyl ethyl ketone, the first step is the oxidation of n-C4H8 with an aqueous solution of Mo-V-P heteropoly acid in the presence of Pd(II) complexes. The kinetics of n-butene oxidation with solutions of H7PV 4Mo8O40 (HPA-4) in the presence of the Pd(II) dipicolinate complex (H2O)PdII(dipic) (I), where dipic2- is the tridentate ligand 2,6-NC5H3(COO-)2, is studied. Calculation shows that, at the ratio dipic2- : Pd(II) = 1 : 1, the ligand decreases the redox potential of the Pd(II)/Pdmet system from 0.92 to 0.73-0.77, due to which Pd(II) is stabilized in reduced solutions of HPA-4. The reaction is first-order with respect to n-C4H8. Its order with respect to Pd(II) is slightly below unity, and its order with respect to HPA-4 is relatively low (~0.63). The activation energy of but-1-ene oxidation in the temperature range from 40 to 80°C is 49.0 kJ/mol, and that of the oxidation of but-2-ene is 55.6 kJ/mol. The mechanism of the reaction involving the cis-diaqua complex [(H2O)2PdII(Hdipic)] +, which forms reversibly from complex I, is proposed. The reaction rate is shown to increase with an increase in the HPA-4 concentration due to an increase in the acidity of the solution. Pleiades Publishing, Ltd., 2011.
- Odyakov,Zhizhina
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- Fast and Selective Semihydrogenation of Alkynes by Palladium Nanoparticles Sandwiched in Metal–Organic Frameworks
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The semihydrogenation of alkynes into alkenes rather than alkanes is of great importance in the chemical industry. Unfortunately, state-of-the-art heterogeneous catalysts hardly achieve high turnover frequencies (TOFs) simultaneously with almost full conversion, excellent selectivity, and good stability. Here, we used metal–organic frameworks (MOFs) containing Zr metal nodes (“UiO”) with tunable wettability and electron-withdrawing ability as activity accelerators for the semihydrogenation of alkynes catalyzed by sandwiched palladium nanoparticles (Pd NPs). Impressively, the porous hydrophobic UiO support not only leads to an enrichment of phenylacetylene around the Pd NPs but also renders the Pd surfaces more electron-deficient, which leads to a remarkable catalysis performance, including an exceptionally high TOF of 13835 h?1, 100 % phenylacetylene conversion 93.1 % selectivity towards styrene, and no activity decay after successive catalytic cycles. The strategy of using molecularly tailored supports is universal for boosting the selective semihydrogenation of various terminal and internal alkynes.
- Choe, Kwanghak,Li, Guodong,Qiu, Xueying,Ri, Myonghak,Shi, Xinghua,Tang, Zhiyong,Wang, Hui,Wang, Yinglong,Xue, Guangxin,Yuan, Yi,Zhao, Wenshi,Zheng, Fengbin
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- Synthesis, characterization, and norbornene polymerization of η3-benzylnickel(II) complexes of N-heterocyclic carbenes
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Neutral η1-benzylnickel carbene complexes, [Ni(η1-CH2C6H5)(IiPr)(PMe3)(Cl)] (3) (IiPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene) and [Ni(η1-CH2C6H5)(SIiPr)(PMe3)(Cl)] (4) (SIiPr = 1,3-bis-(2,6-diisopropylphenyl)imidazolin-2-ylidene), were prepared by the reaction between [Ni(η3-CH2C6H5)(PMe3)(Cl)] and an equivalent amount of the corresponding free N-heterocyclic carbene. The preparation of η3-benzylnickel carbene complexes, [Ni(η3-CH2C6H5)(IiPr)(Cl)] (5) and [Ni(η3-CH2C6H5)(SIiPr)(Cl)] (6) were carried out by the abstraction of PMe3 from 3 and 4 by the treatment of B(C6F5)3. The treatment of AgX on 5 and 6 produced the anion-exchanged complexes, [Ni(η3-CH2C6H5)(NHC)(X)] (7, NHC = IiPr, X = O2CCF3; 8, NHC = IiPr, X = O3SCF3; 9, NHC = SIiPr, X = O2CCF3; 10, NHC = SIiPr, X = O3SCF3). The solid state structures of 3 and 10 were determined by X-ray crystallography. The η3-benzyl complexes of IiPr (5, 7, and 8) alone, in the absence of any activators such as borate and MAO, showed good catalytic activity towards the vinyl-type norbornene polymerization. The catalyst was thermally robust and the activity increases as the temperature rises to 130 °C.
- Sujith,Noh, Eun Kyung,Lee, Bun Yeoul,Han, Jin Wook
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- PROPERTIES OF MAGNESIUM OXIDES PREPARED FROM VARIOUS SALTS AND THEIR CATALYTIC ACTIVITY IN 1-BUTENE ISOMERIZATION.
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The basicity, one-electron donor property, and surface area were examined on the magnesium oxide catalysts prepared from six different kinds of magnesium salts. Magnesium oxide prepared from magnesium nitrate, oxalate, and acetate exhibited strong basicity and relatively large surface area and, on the other hand, MgO prepared from magnesium chloride, carbonate and sulfate had relatively weak basicity and small surface area. Number of one-electron donor centers hardly changed in the variety of magnesium oxides, except the one prepared from magnesium chloride. Isomerization of 1-butene was carried out on the six kinds of catalysts at 30 degree C. The magnesium oxides prepared from nitrate, oxalate, and acetate salts (group A) exhibited isomerization activity and the ones from chloride, sulfate, and carbonate (group B) did not entirely.
- Matsuda,Tanabe,Hayashi,Sasaki,Miura,Sugiyama
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- KOMPLEXKATALYSE. XII. NITRIDO-MOLYBDAEN(VI)-KOMPLEXE; EIN NEUER TYP VON HOCHAKTIVEN PRAEKATALYSATOREN FUER DIE OLEFINMETATHESE
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The preparation of the trichloronitridomolybdenum(VI) complexes MoNCl3(OPPh3)2, MoNCl3(Dipy), and and their suitability as precatalysts for the metathesis of 2-pentene is described.
- Seyferth, Karl,Taube, Rudolf
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- Olefin Dimerization and Isomerization Catalyzed by Pyridylidene Amide Palladium Complexes
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A series of cationic palladium complexes [Pd(N^N′)Me(NCMe)]+ was synthesized, comprising three different N^N′-bidentate coordinating pyridyl-pyridylidene amide (PYA) ligands with different electronic and structural properties depending on the PYA position (o-, m-, and p-PYA). Structural investigation in solution revealed cis/trans isomeric ratios that correlate with the donor properties of the PYA ligand, with the highest cis ratios for the complex having the most donating o-PYA ligand and lowest ratios for that with the weakest donor p-PYA system. The catalytic activity of the cationic complexes [Pd(N^N′)Me(NCMe)]+ in alkene insertion and dimerization showed a strong correlation with the ligand setting. While complexes bearing more electron donating m- and o-PYA ligands produced butenes within 60 and 30 min, respectively, the p-PYA complex was much slower and only reached 50% conversion of ethylene within 2 h. Likewise, insertion of methyl acrylate as a polar monomer was more efficient with stronger donor PYA units, reaching a 32% ratio of methyl acrylate vs ethylene insertion. Mechanistic investigations about the ethylene insertion allowed detection, for the first time, by NMR spectroscopy both cis- and trans-Pd-ethyl intermediates and, furthermore, revealed a trans to cis isomerization of the Pd-ethyl resting state as the rate-limiting step for inducing ethylene conversion. These PYA palladium complexes induce rapid double-bond isomerization of terminal to internal alkenes through a chain-walking process, which prevents both polymerization and also the conversion of higher olefins, leading selectively to ethylene dimerization.
- Navarro, Miquel,Rosar, Vera,Montini, Tiziano,Milani, Barbara,Albrecht, Martin
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- Vitamin B1-Catalyzed Acetoin Formation from Acetaldehyde: A Key Step for Upgrading Bioethanol to Bulk C4Chemicals
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The production of bulk chemicals and fuels from renewable biobased feedstocks is of significant importance for the sustainability of human society. The production of ethanol from biomass has dramatically increased and bioethanol also holds considerable potential as a versatile building block for the chemical industry. Herein, we report a highly selective process for the conversion of ethanol to C4bulk chemicals, such as 2,3-butanediol and butene, via a vitamin B1 (thiamine)-derived N-heterocyclic carbene (NHC)-catalyzed acetoin condensation as the key step to assemble two C2acetaldehydes into a C4product. The environmentally benign and cheap natural catalyst vitamin B1 demonstrates high selectivity (99 %), high efficiency (97 % yield), and high tolerance toward ethanol and water impurities in the acetoin reaction. The results enable a novel and efficient process for ethanol upgrading.
- Lu, Ting,Li, Xiukai,Gu, Liuqun,Zhang, Yugen
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- New Insights in the Catalytic Activity of Cobalt Orthophosphate Co3(PO4)2 from Charge Density Analysis
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An extensive characterization of Co3(PO4)2 was performed by topological analysis according to Bader‘s Quantum Theory of Atoms in Molecules from the experimentally and theoretically determined electron density. This study sheds light on the reactivity of cobalt orthophosphate as a solid-state heterogeneous oxidative-dehydration and -dehydrogenation catalyst. Various faces of the bulk catalyst were identified as possible reactive sites given their topological properties. The charge accumulations and depletions around the two independent five- and sixfold-coordinated cobalt atoms, found in the topological analysis, are correlated to the orientation and population of the d-orbitals. It is shown that the (011) face has the best structural features for catalysis. Fivefold-coordinated ions in close proximity to advantageously oriented vacant coordination sites and electron depletions suit the oxygen lone pairs of the reactant, mainly for chemisorption. This is confirmed both from the multipole refinement as well as from density functional theory calculations. Nearby basic phosphate ions are readily available for C?H activation.
- Keil, Helena,Hellstr?m, Matti,Stückl, Claudia,Herbst-Irmer, Regine,Behler, J?rg,Stalke, Dietmar
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- Catalytic conversion of propan-2-ol and butan-2-ol on carbon nanotubes with different carbon structures Evgeniya
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Cylindrical and conical carbon nanotubes were used as catalysts for the conversion of C3–C4 secondary aliphatic alcohols. The effect of the oxidative and reductive treatment of carbon nanotubes on the catalytic activity, selectivity and the conversion of propan-2-ol and butan-2-ol related to the structure of carbon matrix was revealed.
- Arkhipova, Ekaterina A.,Chernyak, Sergey A.,Ivanov, Anton S.,Lunin, Valery V.,Savilov, Sergey V.,Tveritinova, A.,Zhitnev, Yurii N.
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- The Isomerization of Cyclopropane over Reduced Molybdena-Alumina Catalysts
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The isomerization and metathesis of cyclopropane were carried out over a series of reduced molybdena-alumina catalysts (1.7-13 wt%Mo). The distribution of Mo oxidation states was determined by XPS. The average Mo oxidation state estimated from XPS agreed with that obtained by measuring the O2 consumption on reoxidation for a given catalyst. A good correlation was found between the catalytic activity for the isomerization reaction and the relative intensity of the XPS peak attributed to paired double-bonded Mo (IV) species (as in MoO2). The results indicate a direct relationship between these Mo (IV) species and the coordinative unsaturated sites involved in the formation of metallocyclobutane. The latter is reportedly the intermediate required for the isomerization reaction to take place.
- Oliveros,Perez Zurita,Scott,Goldwasser,Goldwasser,Rondon,Houalla,Hercules
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- A Stable Supported Re Metathesis-Catalyst derived from on SiO2
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An active, stable supported rhenium catalyst for alkene metathesis was formed by heating 4 on SiO2 under a propene-helium atmosphere at 423 K.
- Kirlin, Peter S.,Gates, Bruce C.
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- Catalytic transformation of ethanol to methane and butene over NiO NPs supported over mesoporous SBA-15
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Hexagonally ordered mesoporous silica material SBA-15 with thick pore wall is an ideal catalytic support for immobilizing reactive tiny metal oxide nanoparticles (NPs) due to its large pore size, high specific surface area, excellent feasibility for the i
- Chatterjee, Sauvik,Bhaduri, Kushanava,Modak, Arindam,Selvaraj, Manickam,Bal, Rajaram,Chowdhury, Biswajit,Bhaumik, Asim
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- Reactions of hydroxylamido(-O,N)nitrosyl molybdenum complexes with EtAlCl2; olefin metathesis activity of these systems
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The nitrosyl molybdenum complexes n- (L = X, n = 2; L2 = phen, n = 0; X = Cl-, NCS-, N3), n- (m = 0, 1; L = NCS-, n = 2; L = phen, n = 0) react with EtAlCl2 to form the catalytically active systems for olefin metathesis.The carbene dinitrosyl molybdenum complexes are the real catalysts in these systems.The mechanism by which these complexes are formed was determined from their IR spectra recorded in PhCl in the range 1600-2300 cm-1 i.e. in the ν(NO), Ν(CN), and ν(NN) regions.The synthesis and characterization of the novel complexes (L = Cl- and N3) are described.
- Keller, A.
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- Dehydrogenation of Propan-2-ol to Acetone catalysed by Zirconium Oxide treated with Selenate and Tellurate Ions
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A dehydrogenation catalyst was obtained by exposing Zr(OH)4 to 0.05 M H2SeO4 or H2TeO4 and followed by calcination in air at 600 - 800 deg C; this catalyst converted propan-2-ol into acetone with 100percent selectivity.
- Hino, Makoto,Arata, Kazushi
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- Photoluminescence Evidence for the Influence of Symmetry of Molybdenum Ions upon Photocatalytic Activity
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Photoluminescence studies of supported MoO3 as well as measurements of the photocatalytic reactions on them suggest that tetrahedrally coordinated Mo ions play a significant role in the photocatalytic activity, which first increases and then decreases with increasing MoO3 content accompanied by a symmetry change from tetrahedral to octahedral coordination.
- Anpo, Masakazu,Suzuki, Tetsuo,Kubokawa, Yutaka,Tanaka, Fujio,Yamashita, Shigeru
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- Modulation of N^N′-bidentate chelating pyridyl-pyridylidene amide ligands offers mechanistic insights into Pd-catalysed ethylene/methyl acrylate copolymerisation
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The efficient copolymerisation of functionalised olefins with alkenes continues to offer considerable challenges to catalyst design. Based on recent work using palladium complexes containing a dissymmetric N^N′-bidentate pyridyl-PYA ligand (PYA = pyridylidene amide), which showed a high propensity to insert methyl acrylate, we have here modified this catalyst structure by inserting shielding groups either into the pyridyl fragment, or the PYA unit, or both to avoid fast β-hydrogen elimination. While a phenyl substituent at the pyridyl side impedes catalytic activity completely and leads to an off-cycle cyclometallation, the introduction of an ortho-methyl group on the PYA side of the N^N′-ligand was more prolific and doubled the catalytic productivity. Mechanistic investigations with this ligand system indicated the stabilisation of a 4-membered metallacycle intermediate at room temperature, which has previously been postulated and detected only at 173 K, but never observed at ambient temperature so far. This intermediate was characterised by solution NMR spectroscopy and rationalises, in part, the formation of α,β-unsaturated esters under catalytic conditions, thus providing useful principles for optimised catalyst design.
- ó Máille, Gearóid M.,Albrecht, Martin,Dall'Anese, Anna,Grossenbacher, Philipp,Milani, Barbara,Montini, Tiziano
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- Activity of Supported Tungsten Oxide Catalysts for the Metathesis of Propene
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The activity of several supported tungsten oxide catalysts for the metathesis of propene has been studied under temperature-programmed conditions.WO3/TiO2 was found to be active at moderate temperatures; its activity passes through a maximum when the reaction temperature is decreased from 670 to 450 K.WO3/ZnO is less active and its activity as a function of the reaction temperature goes through a maximum under certain conditions.In contrast to these catalysts and to the earlier reported behaviour of the well known WO3/Al2O3 catalyst, the activity of the WO3/SiO2 catalyst steadily increases for reaction temperatures up to 860 K.In this respect the WO3/SiO2-Al2O3 catalyst behaves like the WO3/SiO2 catalyst and not like the WO3/Al2O3 catalyst.The acidity of the supports has been determined by means of a temperature-programmed desorption technique, using t-butylamine as the adsorbed species.The results of this work do not suggest a relationship between the acidity of the supports and the activity for metathesis.
- Andreini, Amedeo,Mol, Johannes C.
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- COMPLEX CATALYSIS. XX. NITROSYLMOLYBDENUM COMPLEXES PRECATALYSTS FOR OLEFIN METHATHESIS. THE FORMATION AND STABILITY OF A 0Cl(NO)>-CONTAINING INTERMEDIATE AND ITS SIGNIFICANCE FOR THE GENERATION OF THE CATALYTICALLY ACTIVE COMPLEX
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The reaction of the nitrosylmolybdenum complexes MoIICl3(NO)(OPPh3)2 and Mo0Cl2(NO)2(PPh3)2 with EtAlCl2 gives a 0Cl(NO)>-containing intermediate, the formation and further reaction of which were followed by IR-spectroscopy after trapping with CO/PPh3 and Et2NC(S)S-S(S)CNEt2, respectively.The dependences on time and temperature of the formation and decomposition of the "0Cl(NO)>" intermediate were also investigated.By comparison of methathesis activity and the decay of the "0Cl(NO)>" intermediate, the latter was confirmed to be an essential catalyst precursor from which the actual methathesis catalyst, very probably a nitridomolybdenum complex, is formed.
- Seyferth, Karl,Taube, Rudolf
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- Preparation of low carbon olefins on a core-shell K-Fe5C2?ZSM-5 catalyst by Fischer-Tropsch synthesis
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In this study, a core-shell catalyst based on Fe5C2?ZSM-5 (ZSM-5 capped Fe5C2 as active phase) is prepared by the coating-carbonization method for Fischer-Tropsch synthesis (FTS). Further, the designed ZSM-5 zeolites are utilized to screen the low carbon hydrocarbons from the products generated on the iron carbide active centre, and for catalytic disassembly of the long-chain hydrocarbons into low carbon olefins. Prior to utilization, the physical-chemical properties of the prepared catalysts are systematically characterized by various techniques of X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR), and scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM) observations, in addition to the effects of coating-carbonization, molecular sieve coating amount, and K-doping on core-shell iron-based catalysts. Next, the performance of Fischer-Tropsch synthesis is investigated in a micro-fixed bed reactor. The results manifest that, comparing with Fe5C2 and a supported Fe/ZSM-5 catalyst prepared by the traditional impregnation method, the core-shell Fe5C2?ZSM-5 catalysts show higher CO conversion rate, reaction activity and selectivity to low-carbon olefins. Comparatively, the Fe5C2?ZSM-5C catalyst prepared by carbonization after the coating method exhibited more surface area, smaller average pore size, and more reactive active sites, resulting in the improvement of screening of high carbon hydrocarbons and the enhancement of selectivity to low carbon olefins, in comparison to those prepared by the carbonization-coating method. In conclusion, the K-doping catalyst had significantly improved the reactive activity of the core-shell Fe5C2?ZSM-5 catalyst and the selectivity to low carbon olefins, while the CO conversion on K-Fe5C2?ZSM-20C still remained good.
- Liu, Yang,Liu, Yongjun,Shao, Wenli,Zhang, Chenyang,Zhang, Xueqin,Zheng, Yi,Zhou, Weixia
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- Towards a practical development of light-driven acceptorless alkane dehydrogenation
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The efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter-chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom-efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans-[Rh(PMe3) 2(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C4) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations.
- Chowdhury, Abhishek Dutta,Weding, Nico,Julis, Jennifer,Franke, Robert,Jackstell, Ralf,Beller, Matthias
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- A Comparison of Electron Donor and Proton Abstraction Activities of Thermally Activated Pure Magnesium Oxide and Doped Magnesium Oxides
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Thermal activation of microcrystalline MgO at 400-700 deg C has been carried out under vacuum and under rapid flows of N2, Ar, O2, and H2/N2.Some samlpes of MgO were impregnated or coprecipitated with LiOH, NaOH, or Al(OH)3 before activation.The activities for 1-butene isomerization, where proton abstraction is limiting, were compared with activities for CO telomerization/reduction, where electron donation capability is most important.These studies suggest that defect sites are involved and that localized electron rich domains can be enhanced by Li+ substitution for Mg+ but that localized more electron difficient domains can be enhanced by Al3+ substitution for Mg2+.These studies also show that high-temperature thermal activation with gas flow of N2 or Ar is possible, but that O2 and H2/N2 anneal out defects and activity is lost.
- Klabunde, Kenneth J.,Matsuhashi, Hiromi
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- Olefin Rearrangement Resulting from the Gas-Phase KrF Laser Photolysis of Cr(CO)6
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We have found that irradiation of Cr(CO)6-1-butene mixtures in the gas phase with a KrF laser (248 nm) results in the efficient (yield ca. 0.2) isomerisation of 1-butene to 2-butene, in marked contrast to results in solution.The primary photochemical yield is independent of 1-butene pressure and of Cr(CO)6 pressure over wide pressure ranges.Secondary photochemical processes are also found, the importance of which depends upon 1-butene pressure.We also report yields of species Cr(CO)m(PF3)6-m resulting from irradiation of Cr(CO)6-PF3 mixtures at 248 nm.At high dilution -3>, we find relative yields of 0.10, 0.14, 0.73, and 0.03 for Cr(CO)2(PF3)4, Cr(CO)3(PF3)3, Cr(CO)4(PF3)2, and Cr(CO)5PF3, respectively.These results suggest a high degree of transormation following optical excitation at 248 nm.We present a resonable kinetic model to explain the observed isomerization of butene in which a primary photofragment, probably Cr(CO)3 or Cr(CO)2, is the active species.
- Tumas, William,Gitlin, Barbara,Rosan, Alan M.,Yardley, James T.
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- Diastereoselective free radical halogenation, azidation, and rearrangement of β-silyl Barton esters
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(equation presented) Barton esters of β-silylcarboxylic acids were decomposed by photolysis alone in organic solvents or in the presence of ethanesulfonyl azide or bromotrichloromethane. Products of the reaction, β-silylthiopyridyl ethers, β-silyl azides, or alkenes, were formed with significant control of stereochemistry.
- Masterson, Douglas S.,Porter, Ned A.
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- Vapor-phase dehydration of 1,4-butanediol to 1,3-butadiene over Y2Zr2O7 catalyst
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Vapor-phase catalytic dehydration of 1,4-butanediol (1,4-BDO) was investigated over Y2O3-ZrO2 catalysts. In the dehydration, 1,3-butadiene (BD) together with 3-buten-1-ol (3B1OL), tetrahydrofuran, and propylene was produced depending on the reaction conditions. In the dehydration over Y2O3-ZrO2 catalysts with different Y contents at 325°C, Y2Zr2O7 with an equimolar ratio of Y/Zr showed high selectivity to 3B1OL, an intermediate to BD. In the dehydration at 360°C, a BD yield higher than 90% was achieved over the Y2Zr2O7 calcined at 700°C throughout 10 h. In the dehydration of 3B1OL over Y2Zr2O7, however, the catalytic activity affected by the calcination temperature is roughly proportional to the specific surface area of the sample. The highest activity of Y2Zr2O7 calcined at 700 °C for the BD formation from 1,4-BDO is explained by the trade-off relation in the activities for the first-step dehydration of 1,4-BDO to 3B1OL and for the second-step dehydration of 3B1OL to BD. The higher reactivity of 3B1OL than saturated alcohols such as 1-butanol and 2-butanol suggests that the C=C double bond of 3B1OL induces an attractive interaction to anchor the catalyst surface and promotes the dehydration. A probable mechanism for the one-step dehydration of 1,4-BDO to BD was discussed.
- Matsuda, Asami,Matsumura, Yoshitaka,Sato, Satoshi,Yamada, Yasuhiro
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- Synthesis of a ni complex chelated by a [2.2]paracyclophane-functionalized diimine ligand and its catalytic activity for olefin oligomerization
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A diimine ligand having two [2.2]paracyclophanyl substituents at the N atoms (L1) was prepared from the reaction of amino[2.2]paracyclophane with acenaphtenequinone. The ligand re-acts with NiBr2(dme) (dme: 1,2-dimethoxyethane) to form the dibromonickel complex with (R,R) and (S,S) configuration, NiBr2(L1). The structure of the complex was confirmed by X-ray crystallog-raphy. NiBr2(L1) catalyzes oligomerization of ethylene in the presence of methylaluminoxane (MAO) co-catalyst at 10–50 °C to form a mixture of 1-and 2-butenes after 3 h. The reactions for 6 h and 8 h at 25 °C causes further increase of 2-butene formed via isomerization of 1-butene and formation of hexenes. Reaction of 1-hexene catalyzed by NiBr2(L1)–MAO produces 2-hexene via isom-erization and C12 and C18 hydrocarbons via oligomerization. Consumption of 1-hexene of the reaction obeys first-order kinetics. The kinetic parameters were obtained to be ΔG≠ = 93.6 kJ mol?1, ΔH≠ = 63.0 kJ mol?1, and ΔS≠ = ?112 J mol?1deg?1. NiBr2(L1) catalyzes co-dimerization of ethylene and 1-hexene to form C8 hydrocarbons with higher rate and selectivity than the tetramerization of eth-ylene.
- Osakada, Kohtaro,Takeuchi, Daisuke,Tojo, Yoshi-Aki
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- Understanding the Deactivation of Ag?ZrO2/SiO2 Catalysts for the Single-step Conversion of Ethanol to Butenes
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Ag?ZrO2/SBA-16 has recently been found to be efficient for catalyzing the single-step conversion of ethanol to butene (1- and 2-butene mixtures) in the presence of H2. The reaction proceeds via a cascading sequence of reactions over mixed metal and Lewis sites, with the catalyst composition tuned to selectively favor butene formation. However, the catalyst slowly deactivates when evaluated over long reaction times. In this work, we evaluated the lifetime of the Ag?ZrO2/SBA-16 catalyst system for ethanol-to-butene conversion at 325 °C for up to 800 hours on stream. Several characterization techniques were used to elucidate the mechanism(s) by which catalyst deactivation occurs. Coke deposition, Ag particle sintering, and Ag0-to-Ag+ oxidation state change were identified to be the major causes of catalyst deactivation. Coke deposits cover primarily Lewis acid sites which are responsible for aldol condensation, Meerwein-Ponndorf-Verley (MPV) reduction, and dehydration reactions. Ag particle sintering and Ag oxidation state change leads to a reduction in the number of metallic Ag sites responsible for the dehydrogenation/hydrogenation steps. The fresh catalyst likely experiences hydrothermal sintering in the early stage of reaction and permanently loses some active Lewis acid sites before reaching a new structural steady state. The deactivation of Lewis acid sites leads to a decrease in overall ethanol conversion, whereas the deactivation of the metallic Ag sites decreases the butene selectivity. For catalyst regeneration, oxidative calcination (at 500 °C) followed by reduction (at 325 °C) successfully removes all the coke species on the catalyst surface and restores the metallic Ag particles of the 4Ag?4ZrO2/SBA-16 catalysts.
- Lin, Fan,Dagle, Vanessa Lebarbier,Winkelman, Austin D.,Engelhard, Mark,Kovarik, Libor,Wang, Yilin,Wang, Yong,Dagle, Robert,Wang, Huamin
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p. 999 - 1008
(2020/12/18)
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- Bridging the Gap: From Homogeneous to Heterogeneous Parahydrogen-induced Hyperpolarization and Beyond
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Demonstration of parahydrogen-induced polarization effects in hydrogenations catalyzed by heterogeneous catalysts instead of metal complexes in a homogeneous solution has opened an entirely new dimension for parahydrogen-based research, demonstrating its applicability not only for the production of catalyst-free hyperpolarized liquids and gases and long-lived non-equilibrium spin states for potential biomedical applications, but also for addressing challenges of modern fundamental and industrial catalysis including advanced mechanistic studies of catalytic reactions and operando NMR and MRI of reactors. This essay summarizes the progress achieved in this field by highlighting the research contributed to it by our colleague and friend Kirill V. Kovtunov whose scientific career ended unexpectedly and tragically at the age of 37. His role in this research was certainly crucial, further enhanced by a vast network of his contacts and collaborations at the national and international level.
- Chekmenev, Eduard Y.,Goodson, Boyd M.,Bukhtiyarov, Valerii I.,Koptyug, Igor V.
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p. 710 - 715
(2021/04/14)
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- Visible-light-induced formation of thiavinyl 1,3-dipoles: A metal-free [3+2] oxidative cyclization with alkynes as easy access to thiophenes
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A visible-light-induced [3+2] oxidative cyclization of various alkynes with easily available ketene dithioacetals as the previously unknown thiavinyl 1,3-dipoles in the presence of an acridine photosensitizer is reported. A series of multisubstituted thiophenes were achieved regioselectively in ≤98% yields under very mild metal-free conditions without other additives. This reaction could tolerate a wide range of substrates and achieve good efficiency in large-scale syntheses. The reaction mechanism and their applications are described in detail to reveal the reactivity of the new 1,3-dipoles and the selectivity of the reactions.
- Zheng, Baihui,Li, Xiaotong,Song, Yang,Meng, Shuyang,Li, Yifei,Liu, Qun,Pan, Ling
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supporting information
p. 3453 - 3459
(2021/05/31)
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- Tuning supported Ni catalysts by varying zeolite Beta heteroatom composition: effects on ethylene adsorption and dimerization catalysis
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The influence of zeolite heteroatom composition on the electron density and catalytic activity of a supported Ni cation is examined. Ni-[X]-Beta catalysts, where X = Al, Ga, Fe, or dealuminated, were synthesized and characterized with probe molecule adsorption with FTIR spectroscopy and C2H4dimerization catalysis. It was observedviaCO adsorption that supported Ni cations were increasing in electron density in the order: [Fe] > [Ga] > [Al]. C2H4dimerization activity increased with increasing electron density of the Ni cation. Despite similarities in reported acid site strength, the acid sites on [Fe]-Beta in this work had significantly lower activity than those on [Ga]-Beta for the skeletal isomerization of linear butenes as well as C2H4dimerization. Introducing H2as a reactant resulted in a decrease in dimerization activity for Ni-[Al]-Beta and Ni-[Ga]-Beta but an increase for Ni-[Fe]-Beta. The selectivity and activity of Ni-[DeAl]-Beta changed dramatically with the introduction of H2, which subsequently converted all C2H4withca.100% selectivity towards C2H6(even with a lower space velocity relative to without H2). These results demonstrate the ability of heteroatom composition to tune catalysis by using C2H4dimerization catalysis as a test reaction with zeolite Beta supported Ni catalysts.
- Meloni, Michael,Runnebaum, Ron C.
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p. 3393 - 3401
(2021/06/06)
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- Isomerization of 1-Butene to 2-Butene Catalyzed by Metal-Organic Frameworks
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MIL-100 and MIL-101 were synthesized and evacuated to generate a series of heterogeneous catalysts for isomerization of 1-butene. Their crystal structures and pore properties were characterized by PXRD and nitrogen adsorption-desorption techniques. These catalysts showed high catalytic activity for isomerization of 1-butene and high selectivities for 2-butene at room temperature. Moreover, the MIL-101 (Cr) catalyst evacuated at 200 °C exhibited the largest BET surface area of 2759 m2 g-1. At the same time, conversion of 1-butene and the highest selectivity to 2-butene were up to 93.38% and 98.08%, respectively. This work indicated that MOFs containing coordinatively unsaturated metal sites might be promising catalysts for olefin isomerization under mild conditions.
- Sheng, Donghai,Zhang, Ying,Song, Qingxiang,Xu, Guang,Peng, Dandan,Hou, Heqian,Xie, Ronggui,Shan, Dongming,Liu, Pengxiao
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supporting information
p. 51 - 57
(2020/01/03)
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- Understanding the deactivation behavior of Pt/WO3/Al2O3 catalyst in the glycerol hydrogenolysis reaction
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The selective hydrogenolysis of glycerol to 1,3-propanediol is a highly important reaction for both improving the profitability of biodiesel and valorization of biomass. While intensive research efforts have been devoted to enhancing the catalytic activity and selectivity, little is focused on the stability although the latter is of paramount importance to practical applications. In this work, we investigated the stability of Pt/WO3/Al2O3 and observed a continuous deactivation trend during a 700 h time-on-stream run. Neither the leaching of active W nor the coking was responsible for the deactivation. Instead, XRD, HAADF-STEM and CO chemisorption results clearly showed the occurrence of significant aggregation of Pt particles, which caused a remarkable decrease of Pt-WOx interfacial sites. As a consequence, strong Br?nsted acid sites which were in situ formed by H2 dissociation at the Pt-WOx interfacial sites were reduced, leading to the deactivation of the catalyst.
- Lei, Nian,Liu, Fei,Miao, Zhili,Pan, Xiaoli,Wang, Aiqin,Wang, Hua,Zhang, Tao
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p. 1261 - 1267
(2020/03/13)
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- Electrochemical Investigation of Low-Valent Multiply MM Bonded Group VI Dimers: A Standard Chemical Reduction Leads to an Unexpected Product
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The synthesis and investigation of multimetallic complexes bearing metal-metal bonds have been significantly advanced over the last 30 years with exciting applications across many fields. While the outlook for synthetically innovative metal-metal species is promising, the reactivity of the classic M2X6 alkyl dimers (where M = W, Mo; X = CH2CMe3, CH2SiMe3) is still not fully understood. In particular, the redox characteristics of these complexes have not been explored by cyclic voltammetry (CV). Herein, W2(CH2CMe3)6 and Mo2(CH2CMe3)6 (1 and 2, respectively) were characterized using CV to show differing electrochemical behavior between the two species. Stoichiometric reactions, guided by the results of the CV experiments, led to the isolation of an alkylidyne-bridged dimer bearing a rare structural motif, W2(μ-CCMe3)2(CH2CMe3)4 (3). Single-crystal X-ray diffraction (SCXRD) and 1H and 13C nuclear magnetic resonance spectroscopy (NMR) were used to establish the connectivity of the structure in the solid and solution phases. Density functional theory (DFT) calculations on 1-3 and the previously reported W2(CSiMe3)2(CH2SiMe3)4 (4) were used to rationalize the reactivity of 1 to form 3 and the structural differences between 3 and 4. Complexes 3 and 4 constitute a case in which the stereoelectronic properties of the silyl neopentyl ligand can affect differences in structure and bonding.
- Chapovetsky, Alon,Delferro, Massimiliano,Kaphan, David M.,Liu, Cong,Patel, Prajay,Sattelberger, Alfred P.
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p. 4430 - 4436
(2020/12/22)
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- Direct conversion of ethylene to propylene over Ni- and W-based catalysts: An unprecedented behaviour
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A new ethylene to propylene catalytic process based on cascade reactions, with two catalysts and two reactors, has been explored in this study. In the first reactor loaded with Ni-AlKIT-6 catalyst, at 60–120 °C and 3 MPa, part of ethylene has been selectively transformed into 2-butene. In the second reactor, loaded with WOx/KIT-6 catalyst, 2-butene reacted with the unconverted ethylene at 450 °C and 0.1 MPa. Unprecedented results in terms of catalytic activity, selectivity towards the formation of propylene and stability against deactivation were achieved under these conditions. More precisely, an ethylene conversion of ~85% and a selectivity to propylene of 55% and butenes of 30% remained unchanged during 24 h on reaction stream.
- Beucher, Rémi,Cammarano, Claudia,Hulea, Vasile,Rodríguez-Castellón, Enrique
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- Air and Moisture Tolerant Synthesis of a Chelated bis(NHC) Methylpalladium(ii) Complex Relevant to Alkyl Migration Processes in Catalysis
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An air-and moisture-tolerant alternate synthetic pathway to the preparation of a cationic chelated bis(NHC) methylpalladium(ii) complex, [{(MesIm)2CH2}Pd(Me)(NCMe)][PF6], is described. The pathway involves the isolation of a bis(NHC) AgI complex, [{(MesIm)2CH2}2Ag2][PF6]2, via metallation of the corresponding diimidazolium salt with Ag2O followed by carbene transfer to [(COD)PdBrMe]. This new method avoids a previously reported unstable intermediate that displayed rapid decomposition at room temperature, attaining the targeted cationic methylpalladium(ii) complex in high yield. CO/ethylene copolymerisation catalysis trials are reported showing solvent dependent catalyst lifetime and copolymer yields. Preliminary ethylene insertion studies are also outlined revealing possible pathways leading towards catalyst deactivation.
- Gardiner, Michael G.,Ho, Curtis C.,McGuinness, David S.,Liu, Yi Ling
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p. 1158 - 1164
(2020/09/17)
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- PROCESS FOR HYDROGENATION OF 1,3-BUTADIENE
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Methods of improving the selectivity of selective hydrogenation of residual 1,3-butadiene in a C4 fraction of a hydrocarbon raffinate stream in a fixed-bed reactor are described. The methods may include co-feeding a competitive chemical species that increases the mechanistic selectivity to 1- and 2-butenes while increasing isomerization selectivity to 2-butene in the product stream. The hydrogenation reactor and competitive chemical species conditions may be tailored to selectively produce butenes over butane or iso-butane, where the butenes comprise 1 -butene and/or 2-butene.
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Paragraph 0064-0086
(2020/11/12)
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- Silica-Grafted Tris(neopentyl)aluminum: A Monomeric Aluminum Solid Co-catalyst for Efficient Nickel-Catalyzed Ethene Dimerization
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A silica-supported monomeric alkylaluminum co-catalyst was prepared via surface organometallic chemistry by contacting tris(neopentyl)aluminum and partially dehydroxylated silica. This system, fully characterized by solid-state 27Al NMR spectroscopy augmented by computational studies, efficiently activates (nBu3P)2NiCl2 towards dimerization of ethene, demonstrating comparable activity to previously reported dimeric diethylaluminum chloride supported on silica. Three types of aluminum surface species have been identified: monografted tetracoordinated Al species as well as two types of bisgrafted Al species—tetra- and pentacoordinated. Of them, only the monografted Al species is proposed to be able to activate the (nBu3P)2NiCl2 complex and generate the active cationic species.
- Copéret, Christophe,Florian, Pierre,Gordon, Christopher P.,Lesage, Anne,Moroz, Ilia B.,Viger-Gravel, Jasmine
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supporting information
p. 16167 - 16172
(2020/07/04)
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- 2-(: N, N -Diethylaminomethyl)-6,7-trihydroquinolinyl-8-ylideneamine-Ni(ii) chlorides: Application in ethylene dimerization and trimerization
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A series of Ni(ii) complexes with the general formula [2-((NEt2)Me)-8-{N(Ar)}C9H8N]NiCl2, where Ar = 2,6-Me2C6H3 in Ni1, 2,6-Et2C6H3 in Ni2, 2,6-i-Pr2C6H3 in Ni3, 2,4,6-Me3C6H2 in Ni4, 2,6-Et2-4-MeC6H2 in Ni5, and 2,4,6-t-Bu3C6H2 in Ni6, has been prepared using a one-pot reaction of 2-(N,N-diethylaminomethyl)-6,7-dihydroquinolin-8(5H)-one with the corresponding aniline and nickel dichloride hexahydrate. The resultant complexes were characterized using elemental analysis and FT-IR spectroscopy, while the mononuclear Ni1 and Ni3 were also the subject of single-crystal X-ray diffraction study. On activation with MMAO, the complexes Ni1-Ni6 displayed good activity in ethylene oligomerization, forming hexenes (ca. 48% 1-hexene) as the major products and exhibiting thermal stability up to 50 °C under 10 atm C2H4. When MAO was applied as the cocatalyst, lower activity was observed, but the catalyst showed higher selectivity toward ethylene dimerization. It is also worth noticing that an induction period was observed as the Ni/MAO catalysts reached their peak activity after 30 min. This journal is
- Li, Jiaxin,Ma, Yanping,Hu, Xinquan,Flisak, Zygmunt,Tongling, Liang,Sun, Wen-Hua
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p. 17047 - 17052
(2020/10/27)
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- New PtSn structured catalysts with ZnAl2O4 thin film for n-butane dehydrogenation reaction
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Starting from structured supports based on compact spheres coated with a thin and porous layer of ZnAl2O4, mono and bimetallic catalysts were prepared. These catalysts were applied for the n-butane dehydrogenation reaction to produce light olefins. The structured supports were synthesized by coating with: bohemite-nitrate purified method (BP) and citrate-nitrate method (C). From the characterization results, the existence of strong Pt-Sn interaction in both bimetallic catalysts with probable alloys formation was found. In the PtSn/Sp-Zn-C catalyst, where higher metallic Pt-Sn interactions were observed, most of its metallic particles have sizes between 1 and 1.5 nm, which indicates a good metallic dispersion. These properties led to a catalyst with the best catalytic behavior, thus showing high yields to butenes, and a very good stability. Moreover, the presence of a structured support improves the mass and heat transference in this reaction carried out at high temperature.
- de Miguel, Sergio,Ballarini, Adriana,Bocanegra, Sonia
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- Insight in the relationship between magnetism of stoichiometric spinel ferrites and their catalytic activity
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In this work, spinel ferrites were chosen as prototype systems for oxidative dehydrogenation of 1-butene to address the long-standing issue that whether there is a correlation between catalytic and magnetic properties of magnetic catalysts. Under zero magnetic field, the conversion was the largest for NiFe2O4 (74.5 mol%) and the least for ZnFe2O4 (12.6 mol%), with no quantative relationship between magnetism and catalytic activity. In contrast, under a magnetic field of 1603 Oe, the largest and least conversion values changed to 86.6 and 13.5 mol% for MgFe2O4 and ZnFe2O4, respectively, and these values exhibited an inverse Gauss relation with initial susceptibility.
- Chen, Kezheng,Liu, Chunting,Ma, Ji
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- Single-reactor conversion of ethanol to 1-/2-butenes
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A simplified processes for producing desired chemicals such as butenes from feedstock mixtures containing ethanol. In one set of embodiments this is performed in a single step, wherein a feed containing ethanol in a gas phase is passed over an acidic metal oxide catalyst having a transition metal dispersion of at least 5% on a metal oxide support. The ethanol content of the feedstock mixture may vary from 10 to 100 percent of the feed and in those non-eat applications the ethanol feed may contain water.
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(2020/06/03)
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- Detection of Steady State Multiplicity during Dimethyl Ether Conversion Catalyzed by ZnO/γ-Al2O3 Composite: Effect of Coke and Hydrogen Peroxide
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Abstract: The heterogeneous catalytic conversion of dimethyl ether (DME) to 1,3-butadiene and butylenes in the presence of a ZnO/γ-Al2O3 catalyst in a wide range of temperatures, feed space velocities, and reactant concentrations has been studied. It has been found that temperature regions of 380–420 and 440–480°C, which are conventionally designated as low-temperature and high-temperature regions, differ in the laws governing the occurrence of the process associated with the specificity of coking of the catalyst surface and a redistribution of the surface concentration of Br?nsted and Lewis acid sites. A hypothesis of a change of the catalytic process mechanism upon the transition of the reaction into the high-temperature region has been put forward and confirmed by the occurrence of a hysteresis detected in this temperature range. The effect of hydrogen peroxide on the hysteresis parameters and the steady state stability during DME conversion has been shown.
- Maksimov, A. L.,Talyshinskii, R. M.,Tret’yakov, V. F.
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p. 773 - 784
(2020/07/31)
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- Olefin reaction in the catalyst and the olefin production
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PROBLEM TO BE SOLVED: To provide a catalyst for obtaining an olefin in high selectivity with a vicinal diol as a raw material.SOLUTION: A catalyst for olefination reaction for use in a reaction to produce an olefin by a reaction of a polyol, having two adjacent carbon atoms each having a hydroxy group, with hydrogen comprises: a carrier; at least one oxide selected from the group consisting of oxides of the group 6 elements and oxides of the group 7 elements supported on the carrier; and at least one metal selected from the group consisting of silver, iridium, and gold supported on the carrier.SELECTED DRAWING: None
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Paragraph 0145-0146; 0149
(2020/10/31)
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- Oligomerization of Light Olefins Catalyzed by Br?nsted-Acidic Metal-Organic Framework-808
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Sulfated metal-organic framework-808 (S-MOF-808) exhibits strong Br?nsted-acidic character which makes it a potential candidate for the heterogeneous acid catalysis. Here, we report the isomerization and oligomerization reactions of light olefins (C3-C6) over S-MOF-808 at relatively low temperatures and ambient pressure. Different products (dimers, isomers, and heavier oligomers) were obtained for different olefins, and effective C-C coupling was observed between isobutene and isopentene. Among the substrates investigated, facile oligomerization occurred very specifically for the structures with an α-double bond and two substituents at the second carbon atom of the main carbon chain. The possible oligomerization mechanism of light olefins was discussed based on the reactivity and selectivity trends. Moreover, the deactivation and regeneration of S-MOF-808 were investigated. The catalyst deactivates via two mechanisms which predominance depends on the substrate and reaction conditions. Above 110 °C, a loss of acidic sites was observed due to water desorption, and the deactivated catalyst could be regenerated by a simple treatment with water vapor. For C5 substrates and unsaturated ethers, the oligomers with increased molecular weight caused deactivation via blocking of the active sites, which could not be readily reversed. These findings offer the first systematic report on carbocation-mediated olefin coupling within MOFs in which the Br?nsted acidity is associated with the secondary building units of the MOF itself and is not related to any guest substance hosted within its pore system.
- Liu, Ping,Redekop, Evgeniy,Gao, Xiang,Liu, Wen-Chi,Olsbye, Unni,Somorjai, Gabor A.
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supporting information
p. 11557 - 11564
(2019/08/20)
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- Effective Hydrogenolysis of Glycerol to 1,3-Propanediol over Metal-Acid Concerted Pt/WOx/Al2O3 Catalysts
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Selective cleavage of secondary C?O bond is an important yet challenging strategy in glycerol valorization, and the product 1,3-propanediol (1,3-PDO) is of great value in polyester industry. Herein, we report a series of Pt/WOx/Al2O3 catalysts for selective hydrogenolysis of glycerol in a fixed-bed reactor and obtain the highest space-time yield of 1,3-PDO (191.7*10?3 g1,3-PDO h?1 g?1 cat.) to date. Both Pt and W have substantial effects on the 1,3-PDO yield with the optimum Pt/W atomic ratio of 1/2～1/4. Spectroscopy characterizations as well as chemisorption experiments reveal that at the medium domain size of WOx, hydrogen spillover can take place to the greatest extent due to the improved dispersion of Pt and the suitable reducibility of WOx. Dehydration/dehydrogenation tests of 2-butanol suggest that strong Br?nsted acid sites are created via hydrogen dissociation at the Pt?WOx interface and spillover to the neighboring oxygen atom. Such in situ formed protons are critical to the selective cleavage of secondary C?O bonds of polyols.
- Lei, Nian,Zhao, Xiaochen,Hou, Baolin,Yang, Man,Zhou, Maoxiang,Liu, Fei,Wang, Aiqin,Zhang, Tao
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p. 3903 - 3912
(2019/07/18)
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- Catalytic ethylene oligomerization on cobalt(II) bis(imino)pyridine complexes bearing electron-withdrawing groups
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A series of novel bis(imino)pyridine cobalt(II) chlorides, LCoCl2, with the bis(imino)pyridine ligands bearing one or several electron-withdrawing substituents (F, Cl, Br, CF3) at the aniline moieties, have been prepared and characterized. In the presence of methylalumoxane (MAO), these complexes have demonstrated high ethylene oligo- and polymerization activity (up to 1.8·107 g products?(mol Co)?1 h?1 bar?1), affording products ranging from 1-butene and Z,E-2-butenes to strictly linear low-molecular-weight (Mn ～ 300…700) polyethylene. The dependence of the reaction outcome on the ligand structure is discussed.
- Antonov, Artem A.,Semikolenova, Nina V.,Talsi, Evgenii P.,Bryliakov, Konstantin P.
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- METHODS OF FORMING PROPYLENE AND ALKYLATE
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Methods of forming propylene and alkylate are provided. The methods may include providing a stream that includes n-butenes, and contacting the stream with ethylene in the presence of a disproportionation catalyst to form a stream that includes propylene. Propylene then may be removed from the stream, and the stream may be disposed in an alkylation unit to form alkylate.
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Paragraph 0049-0053
(2019/09/20)
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- Crystallographic Visualization of Postsynthetic Nickel Clusters into Metal-Organic Framework
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Postsynthetic metalation (PSM) has been employed as a robust method for the postsynthetic modification of metal-organic frameworks (MOFs). However, the lack of relevant information that can be obtained for the postsynthetically introduced metallic ions has hindered the development of PSM applications. Thanks to the advancement in single-crystal X-ray diffraction (SCXRD) technology, there have been a few recent examples in which successful postsynthetic introduction of single metal ions into MOFs occurred at the defined chelating sites. These works have provided useful explanations about the complicated host-guest chemistry involved in PSMs. On the other hand, there are only limited examples with crystallographic snapshots of the postsynthetic installation of metal clusters into the pores of MOFs using an ordinary SCXRD due to the loss of crystallinity of parent matrix during the PSM process. Herein, by the careful selection of starting materials and controlling the reaction conditions, we report the first crystallographic visualization of metal clusters inserted into Zr-based MOFs via PSM. The structural advantages of the parent Zr-MOF, which are inherited from the stable Zr6 cluster and triazole-containing dicarboxylate ligand, ensure both the preservation of high crystallinity and the presence of flexible coordination sites for PSM. Furthermore, PSM of metal clusters in a MOF pore space enhances stability of the final samples while also imparting the functionality of a successful catalyst toward ethylene dimerization reaction. The related construction ideas and structural information detailed in this work can help lay the foundation for further advancements using the postmodification of MOFs as well as open new doors for the utilization of SCXRD technology in the field of MOFs.
- Wang, Xiao-Ning,Zhang, Peng,Kirchon, Angelo,Li, Jia-Luo,Chen, Wen-Miao,Zhao, Yu-Meng,Li, Bao,Zhou, Hong-Cai
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supporting information
p. 13654 - 13663
(2019/09/10)
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- Exploring C(sp3)–C(sp3) reductive elimination from an isolable iron metallacycle
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A six-coordinate iron metallacyclopentane, (phen)2Fe(CH2)4, supported by two 1,10-phenanthroline (phen) ligands, has been synthesized and structurally and spectroscopically characterized. The complex is diamagnetic and an idealized octahedral geometry was observed in the solid state. The electronic structure of (phen)2Fe(CH2)4 was determined by a combination of X-ray diffraction, M?ssbauer spectroscopy, and DFT analyses and is best described as a low-spin Fe(III) center antiferromagnetically coupled to a radical anion delocalized equally over both phen ligands. The reactivity of (phen)2Fe(CH2)4 under different conditions was explored. Thermolysis or photolysis promoted elimination reactions and mixtures of isomeric butenes and butane were observed. Reactions of (phen)2Fe(CH2)4 with ethylene and isoprene yielded 3% and 11% of reductive elimination product cyclobutane, respectively, along with butane and butene isomers. Addition of π-accepting ligands such as carbon monoxide, maleic anhydride, or 1,4-benzoquinone to (phen)2Fe(CH2)4 promoted C(sp3)-C(sp3) reductive elimination as judged by high selectivity for cyclobutane formation. Two electron oxidation of (phen)2Fe(CH2)4 with two equivalents of ferrocenium tetraphenylborate also exclusively yielded cyclobutane in 95% yield. The electronic structure and reactivity of related bis(bipyridine) iron dialkyl compounds previously isolated by Kochi and co-workers were also revisited and their electronic structures revised based on structural, spectroscopic and computational data.
- Joannou, Matthew V.,Darmon, Jonathan M.,Bezdek, Máté J.,Chirik, Paul J.
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p. 308 - 317
(2019/01/04)
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- Tin-Assisted Fully Exposed Platinum Clusters Stabilized on Defect-Rich Graphene for Dehydrogenation Reaction
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Tin-assisted fully exposed Pt clusters are fabricated on the core-shell nanodiamond@graphene (ND@G) hybrid support (a-PtSn/ND@G). The obtained atomically dispersed Pt clusters, with an average Pt atom number of 3, were anchored over the ND@G support by the assistance of Sn atoms as a partition agent and through the Pt-C bond between Pt clusters and defect-rich graphene nanoshell. The atomically dispersed Pt clusters guaranteed a full metal availability to the reactants, a high thermal stability, and an optimized adsorption/desorption behavior. It inhibits the side reactions and enhances catalytic performance in direct dehydrogenation of n-butane at a low temperature of 450 °C, leading to >98% selectivity toward olefin products, and the turnover frequency (TOF) of a-PtSn/ND@G is ～3.9 times higher than that of the traditional Pt3Sn alloy catalyst supported on Al2O3 (Pt3Sn/Al2O3).
- Zhang, Jiayun,Deng, Yuchen,Cai, Xiangbin,Chen, Yunlei,Peng, Mi,Jia, Zhimin,Jiang, Zheng,Ren, Pengju,Yao, Siyu,Xie, Jinglin,Xiao, Dequan,Wen, Xiaodong,Wang, Ning,Liu, Hongyang,Ma, Ding
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p. 5998 - 6005
(2019/06/24)
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- Ethanol to Butanol Conversion over Bifunctional Zeotype Catalysts Containing Palladium and Zirconium
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Abstract: A study of the kinetics of ethanol conversion in the presence of Zr-containing zeolites BEA doped with palladium particles has revealed the order of formation of the main reaction products. It has been shown that the primary processes are ethanol dehydrogenation to acetaldehyde on Pd sites and ethanol dehydration to diethyl ether on the acid sites of the catalyst. After that, acetaldehyde undergoes the aldol–croton condensation reaction to form crotonal, which is hydrogenated to butanol on the metal sites. Butanol, in turn, is dehydrated into butenes, which undergo hydrogenation to butane. The presence of hydrogen in the gas phase leads to the displacement of ethanol from the metal surface and prevents the formation of surface carbonates and acetates. It has been found that hydrogen significantly accelerates ethanol dehydration owing to a decrease in the activation energy, which can be attributed to hydrogen spillover to the zeolite. The addition of water inhibits all acid-catalyzed reactions owing to competitive adsorption on acid sites and thereby decreases the butanol yield and the ethanol conversion.
- Kots,Zabilska,Grigor’ev, Yu. V.,Ivanova
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p. 925 - 934
(2019/08/20)
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- OLEFIN METATHESIS METHOD USING A CATALYST CONTAINING ALUMINIUM AND MOLYBDENUM INCORPORATED BY MEANS OF AT LEAST TWO PRECURSORS
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The invention relates to a process for the metathesis of olefins implemented with a catalyst comprising a mesoporous matrix and at least the elements molybdenum and aluminium, said elements being incorporated into said matrix by means of at least two precursors of which at least one precursor contains molybdenum and at least one precursor contains aluminium.
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Paragraph 0144-0148
(2018/08/30)
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- OLEFIN METATHESIS METHOD USING A CATALYST CONTAINING ALUMINIUM AND MOLYBDENUM
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The invention relates to a process for the metathesis of olefins implemented with a catalyst comprising a mesoporous matrix and at least the elements molybdenum and aluminium, said elements being incorporated into said matrix by means of at least one precursor comprising molybdenum and aluminium.
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Paragraph 0103-0105
(2018/08/25)
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- Selective Production of Propylene and 1-Butene from Ethylene by Catalytic Cascade Reactions
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In this study, we report that ethylene can be simultaneously and selectively converted into propylene and 1-butene through one-pot catalytic cascade reactions. In a single-continuous-flow reactor and under identical mild conditions (60 °C, 3 MPa), without the use of cocatalyst, ethylene was first dimerized/isomerized over Ni-AlKIT-6 catalysts to form butenes, which reacted then with the excess of ethylene over ReOx/Al2O3 to produce propylene and 1-butene with more than 86% total selectivity. The selectivity for 1-butene was 97.4% in the C4 fraction. The initial ethylene conversion was 73% and stabilized at 35% after 4 h on stream, with around 45% selectivity in propylene and 42% selectivity in 1-butene.
- Beucher, Rémi,Andrei, Radu Dorin,Cammarano, Claudia,Galarneau, Anne,Fajula, Fran?ois,Hulea, Vasile
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p. 3636 - 3640
(2018/04/14)
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- Mechanism of byproducts formation in the isobutane/butene alkylation on HY zeolites
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Submicron-size HY zeolites with a particles size of 200-700 nm were synthesized employing a crystal precipitation method in this study. The catalytic activity for the isobutane/butene alkylation was evaluated. The results indicated that butene conversion was above 90% and the selectivity of expected products (C8) was nearly at 90% within 72 h. The micropores-blocking and coverage of acid sites resulting from high hydrocarbons increased the difficulty for the diffusion of products to the bulk and inhibited the adsorption of reactant on activity sites, which caused deactivation of catalyst. The ultimate C12 content in alkylate oil, stemmed from trimerization of butene, was reduced via the addition reaction with butene to C16 and the cracking to C5-C7. The formation mechanisms and transformation processes of byproducts in alkylate oil revealed that the source of C9-C11 switched from cracking of C16+ to the addition of C5-C7 carbocations with butene when acid sites concentration was reduced by accumulating oligomers.
- Chen, Zhiwei,Gao, Feng,Ren, Kun,Wu, Quangui,Luo, Yan,Zhou, Hongjun,Zhang, Meng,Xu, Quan
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p. 3392 - 3398
(2018/02/07)
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- The Ti3AlC2 MAX Phase as an Efficient Catalyst for Oxidative Dehydrogenation of n-Butane
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Dehydrogenation or oxidative dehydrogenation (ODH) of alkanes to produce alkenes directly from natural gas/shale gas is gaining in importance. Ti3AlC2, a MAX phase, which hitherto had not been used in catalysis, efficiently catalyzes the ODH of n-butane to butenes and butadiene, which are important intermediates for the synthesis of polymers and other compounds. The catalyst, which combines both metallic and ceramic properties, is stable for at least 30 h on stream, even at low O2:butane ratios, without suffering from coking. This material has neither lattice oxygens nor noble metals, yet a unique combination of numerous defects and a thin surface Ti1?yAlyO2?y/2 layer that is rich in oxygen vacancies makes it an active catalyst. Given the large number of compositions available, MAX phases may find applications in several heterogeneously catalyzed reactions.
- Ng, Wesley H. K.,Gnanakumar, Edwin S.,Batyrev, Erdni,Sharma, Sandeep K.,Pujari, Pradeep K.,Greer, Heather F.,Zhou, Wuzong,Sakidja, Ridwan,Rothenberg, Gadi,Barsoum, Michel W.,Shiju, N. Raveendran
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supporting information
p. 1485 - 1490
(2018/01/15)
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- A Systematic Study of Isomorphically Substituted H-MAlPO-5 Materials for the Methanol-to-Hydrocarbons Reaction
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Substituting metals for either aluminum or phosphorus in crystalline, microporous aluminophosphates creates Br?nsted acid sites, which are well known to catalyze several key reactions, including the methanol to hydrocarbons (MTH) reaction. In this work, we synthesized a series of metal-substituted aluminophosphates with AFI topology that differed primarily in their acid strength and that spanned a predicted range from high Br?nsted acidity (H-MgAlPO-5, H-CoAlPO-5, and H-ZnAlPO-5) to medium acidity (H-SAPO-5) and low acidity (H-TiAlPO-5 and H-ZrAlPO-5). The synthesis was aimed to produce materials with homogenous properties (e.g. morphology, crystallite size, acid-site density, and surface area) to isolate the influence of metal substitution. This was verified by extensive characterization. The materials were tested in the MTH reaction at 450 °C by using dimethyl ether (DME) as feed. A clear activity difference was found, for which the predicted stronger acids converted DME significantly faster than the medium and weak Br?nsted acidic materials. Furthermore, the stronger Br?nsted acids (Mg, Co and Zn) produced more light alkenes than the weaker acids. The weaker acids, especially H-SAPO-5, produced more aromatics and alkanes, which indicates that the relative rates of competing reactions change upon decreasing the acid strength.
- Mortén, Magnus,Mentel, ?ukasz,Lazzarini, Andrea,Pankin, Ilia A.,Lamberti, Carlo,Bordiga, Silvia,Crocellà, Valentina,Svelle, Stian,Lillerud, Karl Petter,Olsbye, Unni
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p. 484 - 495
(2017/12/26)
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- Encapsulation of Crabtree's Catalyst in Sulfonated MIL-101(Cr): Enhancement of Stability and Selectivity between Competing Reaction Pathways by the MOF Chemical Microenvironment
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Crabtree's catalyst was encapsulated inside the pores of the sulfonated MIL-101(Cr) metal–organic framework (MOF) by cation exchange. This hybrid catalyst is active for the heterogeneous hydrogenation of non-functionalized alkenes either in solution or in the gas phase. Moreover, encapsulation inside a well-defined hydrophilic microenvironment enhances catalyst stability and selectivity to hydrogenation over isomerization for substrates bearing ligating functionalities. Accordingly, the encapsulated catalyst significantly outperforms its homogeneous counterpart in the hydrogenation of olefinic alcohols in terms of overall conversion and selectivity, with the chemical microenvironment of the MOF host favouring one out of two competing reaction pathways.
- Grigoropoulos, Alexios,McKay, Alasdair I.,Katsoulidis, Alexandros P.,Davies, Robert P.,Haynes, Anthony,Brammer, Lee,Xiao, Jianliang,Weller, Andrew S.,Rosseinsky, Matthew J.
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supporting information
p. 4532 - 4537
(2018/03/26)
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- Synthesis of Densely Packaged, Ultrasmall Pt02 Clusters within a Thioether-Functionalized MOF: Catalytic Activity in Industrial Reactions at Low Temperature
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The gram-scale synthesis, stabilization, and characterization of well-defined ultrasmall subnanometric catalytic clusters on solids is a challenge. The chemical synthesis and X-ray snapshots of Pt02 clusters, homogenously distributed and densely packaged within the channels of a metal–organic framework, is presented. This hybrid material catalyzes efficiently, and even more importantly from an economic and environmental viewpoint, at low temperature (25 to 140 °C), energetically costly industrial reactions in the gas phase such as HCN production, CO2 methanation, and alkene hydrogenations. These results open the way for the design of precisely defined catalytically active ultrasmall metal clusters in solids for technically easier, cheaper, and dramatically less-dangerous industrial reactions.
- Mon, Marta,Rivero-Crespo, Miguel A.,Ferrando-Soria, Jesús,Vidal-Moya, Alejandro,Boronat, Mercedes,Leyva-Pérez, Antonio,Corma, Avelino,Hernández-Garrido, Juan C.,López-Haro, Miguel,Calvino, José J.,Ragazzon, Giulio,Credi, Alberto,Armentano, Donatella,Pardo, Emilio
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supporting information
p. 6186 - 6191
(2018/05/30)
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- The deactivation of a ZnO doped ZrO2-SiO2 catalyst in the conversion of ethanol/acetaldehyde to 1,3-butadiene
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A deactivation study on the ethanol/acetaldehyde conversion to 1,3-butadiene over a ZnO promoted ZrO2-SiO2 catalyst prepared by a sol-gel method was performed. The samples were characterized by N2 adsorption-desorption isotherms, scanning electron microscopy (SEM), NH3 temperature programmed desorption (NH3-TPD), X-ray powder diffraction characterization (XRD), thermogravimetric analyses (TGA), Fourier transform infrared resonance (FT-IR), 13C magic-angle spinning nuclear magnetic resonance (13C NMR) and X-ray photoelectron spectroscopy (XPS). The pore structure characteristics and surface acidity of Zn0.5-Zr-Si catalysts were largely decreased with time-on-stream and no crystal structure was formed in the used catalyst, indicating that the deactivation was caused by carbon deposition. Two main types of carbon deposition were formed, namely low-temperature carbon deposition with the oxidation temperature of around 400 °C and high-temperature carbon deposition with the oxidation temperature of 526 °C. The carbon species were mainly composed of graphitized carbon, amorphous carbon, carbon in C-O bonds and carbonyls. The deactivated catalyst could be regenerated by a simple oxidation process in air. Adding a certain amount of water into the feed had a positive effect on reducing the carbon deposition.
- Zhang, Minhua,Tan, Xuechao,Zhang, Tong,Han, Zheng,Jiang, Haoxi
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p. 34069 - 34077
(2018/10/20)
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- C-H Activation and Proton Transfer Initiate Alkene Metathesis Activity of the Tungsten(IV)-Oxo Complex
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In alkene metathesis, while group 6 (Mo or W) high-oxidation state alkylidenes are accepted to be key reaction intermediates for both homogeneous and heterogeneous catalysts, it has been proposed that low valent species in their +4 oxidation state can serve as precatalysts. However, the activation mechanism for these latter species - generating alkylidenes - is still an open question. Here, we report the syntheses of tungsten(IV)-oxo bisalkoxide molecular complexes stabilized by pyridine ligands, WO(OR)2py3 (R = CMe(CF3)2 (2a), R = Si(OtBu)3 (2b), and R = C(CF3)3 (2c); py = pyridine), and show that upon activation with B(C6F5)3 they display alkene metathesis activities comparable to W(VI)-oxo alkylidenes. The initiation mechanism is examined by kinetic, isotope labeling and computational studies. Experimental evidence reveals that the presence of an allylic CH group in the alkene reactant is crucial for initiating alkene metathesis. Deuterium labeling of the allylic C-H group shows a primary kinetic isotope effect on the rate of initiation. DFT calculations support the formation of an allyl hydride intermediate via activation of the allylic C-H bond and show that formation of the metallacyclobutane from the allyl "hydride" involves a proton transfer facilitated by the coordination of a Lewis acid (B(C6F5)3) and assisted by a Lewis base (pyridine). This proton transfer step is rate determining and yields the metathesis active species.
- Chan, Ka Wing,Lam, Erwin,D'Anna, Vincenza,Allouche, Florian,Michel, Carine,Safonova, Olga V.,Sautet, Philippe,Copéret, Christophe
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supporting information
p. 11395 - 11401
(2018/09/06)
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- Oxidative Dehydrogenation of 1-Butene to 1,3-Butadiene over a Multicomponent Bismuth Molybdate Catalyst: Influence of C3–C4 Hydrocarbons
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Abstract: The influence of light hydrocarbons, such as n-butane, isobutane, propylene, cis- and trans-2-butenes, and isobutene on the oxidative dehydrogenation of 1-butene to 1,3-butadiene over BiMoKNiCoFePOx/SiO2catalyst has been studied using a gas flow reactor. The inhibition effect of the listed hydrocarbons on the target reaction increased in the order of n-butane ~ isobutane propylene 2-butenes isobutene. In addition, in contrast to 1-butene, isobutene has shown significant contribution to coke formation. It was suggested, that the coke formation and therefore the rate of the catalyst regeneration exercise a significant influence on the efficiency of 1-butene transformation into 1,3-butadiene in the concurrent presence of other hydrocarbons. Graphical Abstract: [Figure not available: see fulltext.]
- Sobolev, Vladimir I.,Koltunov, Konstantin Yu.,Zenkovets, Galina A.
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p. 310 - 317
(2017/02/18)
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- For low-carbon alkane dehydrogenation to olefin of vanadium-based catalyst, preparation method and process thereof (by machine translation)
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The invention relates to a for low-carbon alkane dehydrogenation of olefins, to solve the problems existing in the vanadium-based catalyst when of high loading low dispersity, active component easily for crystallization, in high-temperature conditions of low selectivity, one-way the problem of poor stability. The invention through a used for low carbon alkane dehydrogenation to olefin supported vanadium-based catalyst and its preparation method, the catalyst in order to silicon-based material is used as a carrier, dipping or its oxide as the active component, the synthetic method to prepare, in low-O2 Concentration in order to oxidative dehydrogenation and direct dehydrogenation the way to combine catalytic low carbon alkane dehydrogenation reaction of olefins, finally the technical proposal of the burning charcoal catalyst regeneration, better solves the problem, can be used for low-carbon alkane dehydrogenation in the industrial production of light olefins. (by machine translation)
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Paragraph 0057-0060
(2017/07/12)
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- Solid-state molecular organometallic chemistry. Single-crystal to single-crystal reactivity and catalysis with light hydrocarbon substrates
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Single-crystal to single-crystal solid/gas reactivity and catalysis starting from the precursor sigma-alkane complex [Rh(Cy2PCH2CH2PCy2)(η2η2-NBA)][BArF4] (NBA = norbornane; ArF = 3,5-(CF3)2C6H3) is reported. By adding ethene, propene and 1-butene to this precursor in solid/gas reactions the resulting alkene complexes [Rh(Cy2PCH2CH2PCy2)(alkene)x][BArF4] are formed. The ethene (x = 2) complex, [Rh(Cy2PCH2CH2PCy2)(ethene)2][BArF4]-Oct, has been characterized in the solid-state (single-crystal X-ray diffraction) and by solution and solid-state NMR spectroscopy. Rapid, low temperature recrystallization using solution methods results in a different crystalline modification, [Rh(Cy2PCH2CH2PCy2)(ethene)2][BArF4]-Hex, that has a hexagonal microporous structure (P6322). The propene complex (x = 1) [Rh(Cy2PCH2CH2PCy2)(propene)][BArF4] is characterized as having a π-bound alkene with a supporting γ-agostic Rh?H3C interaction at low temperature by single-crystal X-ray diffraction, variable temperature solution and solid-state NMR spectroscopy, as well as periodic density functional theory (DFT) calculations. A fluxional process occurs in both the solid-state and solution that is proposed to proceed via a tautomeric allyl-hydride. Gas/solid catalytic isomerization of d3-propene, H2CCHCD3, using [Rh(Cy2PCH2CH2PCy2)(η2η2-NBA)][BArF4] scrambles the D-label into all possible positions of the propene, as shown by isotopic perturbation of equilibrium measurements for the agostic interaction. Periodic DFT calculations show a low barrier to H/D exchange (10.9 kcal mol-1, PBE-D3 level), and GIPAW chemical shift calculations guide the assignment of the experimental data. When synthesized using solution routes a bis-propene complex, [Rh(Cy2PCH2CH2PCy2)(propene)2][BArF4], is formed. [Rh(Cy2PCH2CH2PCy2)(butene)][BArF4] (x = 1) is characterized as having 2-butene bound as the cis-isomer and a single Rh?H3C agostic interaction. In the solid-state two low-energy fluxional processes are proposed. The first is a simple libration of the 2-butene that exchanges the agostic interaction, and the second is a butene isomerization process that proceeds via an allyl-hydride intermediate with a low computed barrier of 14.5 kcal mol-1. [Rh(Cy2PCH2CH2PCy2)(η2η2-NBA)][BArF4] and the polymorphs of [Rh(Cy2PCH2CH2PCy2)(ethene)2][BArF4] are shown to be effective in solid-state molecular organometallic catalysis (SMOM-Cat) for the isomerization of 1-butene to a mixture of cis- and trans-2-butene at 298 K and 1 atm, and studies suggest that catalysis is likely dominated by surface-active species. [Rh(Cy2PCH2CH2PCy2)(η2η2-NBA)][BArF4] is also shown to catalyze the transfer dehydrogenation of butane to 2-butene at 298 K using ethene as the sacrificial acceptor.
- Chadwick, F. Mark,McKay, Alasdair I.,Martinez-Martinez, Antonio J.,Rees, Nicholas H.,Kr?mer, Tobias,Macgregor, Stuart A.,Weller, Andrew S.
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p. 6014 - 6029
(2017/08/29)
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- Catalyst and process for the conversion of oxygenates to olefins
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The present invention relates to a catalyst for the conversion of oxygenates to olefins, wherein the catalyst comprises one or more zeolites of the MFI, MEL and/or MWW structure type and particles of one or more metal oxides, the one or more zeolites of the MFI, MEL and/or MWW structure type comprising one or more alkaline earth metals, and the particles of the one or more metal oxides comprising phosphorus, the phosphorus being present at least partly in oxidic form, and the one or more alkaline earth metals being selected from the group consisting of Mg, Ca, Sr, Ba and combinations of two or more thereof, to the preparation and use thereof, and to a process for converting oxygenates to olefins using the catalyst.
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Page/Page column 31
(2017/04/11)
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