- Insights into the reaction pathway of hydrodeoxygenation of dibenzofuran over MgO supported noble-metals catalysts
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Conversion of oxygen-containing compounds derived from lignin arises wide interest due to fossil-derived resources consumption and growing environmental concerns. In this work, hydrodeoxygenation (HDO) of dibenzofuran (DBF) was studied over high-surface-area MgO supported Pt, Pd and Ru catalysts at 370 °C and 1.0 MPa. It was determined that the active metals not only affect the catalytic activity, but also change the reaction pathway of HDO of DBF. The intrinsic activity (TOF) of MgO supported catalysts follows the trend: Pt/MgO (0.36 s?1) > Ru/MgO (0.29 s?1) > Pd/MgO (0.09 s?1), companied by the increasing activate barrier. Pt has a high activity in the hydrogenation of DBF, and exhibits a perfect deoxygenation activity followed by hydrogenation (HYD) pathway. Ru shows better cleavage ability of Caromatic–O bond and the removal of oxygen from DBF mainly occurs via direct deoxygenation (DDO) pathway. The increased Pt loadings largely promote the conversion of DBF by enhancing both HYD and DDO pathways. In addition, more direct cleavage of Caromatic–O bond occurs at higher temperature and the production of aromatics by the DDO pathway prefers the relatively low reaction pressure. Based on the pseudo-first-order kinetics, the analysis of the fitted reaction rate constant shows that the DDO selectivity follows the order: Ru/MgO > Pd/MgO > Pt/MgO, which depends on the capacity of active metals to the cleavage of Caromatic–O bond and the hydrogenation of aromatic ring.
- Zhang, Jie,Li, Chuang,Chen, Xiao,Guan, Weixiang,Liang, Changhai
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- On the synthesis and optical absorption studies of nano-size magnesium oxide powder
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Magnesium oxide (MgO) nano-size powder is synthesized using magnesium nitrate hexahydrate and oxalic acid as precursors with ethanol as a solvent. The process involves gel formation, drying at 100 °C for 24 h to form magnesium oxalate dihydrate [α-MgC2O4 · 2H 2O] and its decomposition at 500, 600, 800, and 1000 °C for 2 h to yield MgO powder (average crystallite size ~6.5-73.5 nm). The sol-gel products at various stages of synthesis are characterized for their thermal behaviour, phase, microstructure, optical absorption, and presence of hydroxyl and other groups like o = C = O, C = O, C-C, etc. MgO powder is shown to possess an f.c.c. (NaCl-type) structure with lattice parameter increasing with decrease in crystallite size (tav); typical value being ~4.222(2) A? for tav~6.5nm as against the bulk value of 4.211 A?. Infrared absorption has shown MgO to be highly reactive with water. Also, a variety of F- and M-defect centres found in MgO produce energy levels within the band gap (7.8 eV), which make it attractive for application in plasma displays for increasing secondary electron emission and reducing flickering effects. The possible application of the intermediate sol-gel products, viz., α-MgC2O4 · 2H2O and anhydrous magnesium oxalate (MgC2O4) in understanding the plants and ESR dosimetry, respectively, has also been suggested.
- Kumar, Ashok,Kumar, Jitendra
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- Kinetics of the Thermal Dehydration of Magnesium Oxalate Dihydrate in a Flowing Atmosphere of Dry Nitrogen
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The kinetics of isothermal dehydration of MgC2O4*2H2O in a dry nitrogen flow have been studied in detail by use of many accurate thermogravimetric data acquired on a microcomputer.This dehydration proceeded as a two-dimensional phase boundary reaction, R2.In general, the nucleation in the phase boundary reaction occurs so rapidly that the reaction rate is only determined by following the chemical process occurring at the reactant-product interface.However, the present dehydration was affected by the nucleation process, and its dehydration fraction curve showed a sigmoid character especially at lower temperatures than ca. 160 deg C.We succeeded in separately evaluating the rate constants kN for the nucleation and k2 for the R2 process by detailed analysis of the dehydration fraction curve.The value of kN became comparable to that of k2 at lower temperatures whereas at higher temperature the former became much larger than the latter and the overall dehydration had a characteristic of natural R2 reaction.The values of activation energies and preexponential factors for both processes were determined from the temperature dependency of kN and k2.Those were 430 kJ mol-1 and 3.73*1049 s-1 for the nucleation process, and 111 kJ mol-1 and 3.40*109 s-1 for two-dimensional phase boundary process, respectively.
- Masuda, Yoshio,Iwata, Keiichi,Ito, Ryokou,Ito, Yoshio
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- Mechanistic Insight into Caffeine-Oxalic Cocrystal Dissociation in Formulations: Role of Excipients
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Caffeine-oxalic acid cocrystal, widely reported to be stable under high humidity, dissociated in the presence of numerous pharmaceutical excipients. In cocrystal-excipient binary systems, the water mediated dissociation reaction occurred under pharmaceutically relevant storage conditions. Powder X-ray diffractometry was used to identify the dissociated products obtained as a consequence of coformer-excipient interaction. The proposed cocrystal dissociation mechanism involved water sorption, dissolution of cocrystal and excipient in the sorbed water, proton transfer from oxalic acid to the excipient, and formation of metal salts and caffeine hydrate. In compressed tablets with magnesium stearate, the cocrystal dissociation was readily discerned from the appearance of peaks attributable to caffeine hydrate and stearic acid. Neutral excipients provide an avenue to circumvent the risk of water mediated cocrystal dissociation.
- Duggirala, Naga Kiran,Vyas, Amber,Krzyzaniak, Joseph F.,Arora, Kapildev K.,Suryanarayanan, Raj
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p. 3879 - 3887
(2017/11/15)
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- Mimicking mineral neogenesis for the clean synthesis of metal-organic materials from mineral feedstocks: Coordination polymers, MOFs and metal oxide separation
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We present a systematic study of a mild approach for the activation of metal oxides, involving reactivity and self-assembly in the solid state, which enables their solvent-free chemical separation and direct solvent-free and low-energy conversion into coordination polymers and open metal-organic frameworks (MOFs). The approach is inspired by geological biomineralization processes known as mineral weathering, in which long-term exposure of oxide or sulfide minerals to molecules of biological origin leads to their conversion into simple coordination polymers. This proof-of-principle study shows how mineral neogenesis can be mimicked in the laboratory to provide coordination polymers directly from metal oxides without a significant input of either thermal or mechanical energy, or solvents. We show that such "aging" is accelerated by increased humidity, a mild temperature increase and/or brief mechanical activation, enabling the transformation of a variety of high-melting (800 °C-2800 °C) transition (MnII, CoII, Ni II, CuII, and Zn) and main group (Mg and PbII) oxides at or near room temperature. Accelerated aging reactions are readily scaled to at least 10 grams and can be templated for the synthesis of two-dimensional and three-dimensional anionic frameworks of Zn, Ni(ii) and Co(ii). Finally, we demonstrate how this biomineralization-inspired approach provides an unprecedented opportunity for solvent-free chemical segregation of base metals, such as Cu, Zn and Pb, in their oxide form under mild conditions.
- Qi, Feng,Stein, Robin S.,Friscic, Tomislav
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supporting information
p. 121 - 132
(2014/01/06)
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- IN-SITU TREATMENT OF ASBESTOS-CONTAINING MATERIAL
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The present invention relates to methods for the in-situ treatment of ACM containing chrysotile asbestos using a polycarboxylic acid such as oxalic acid. The polycarboxylic acid is introduced to the ACM while it remains substantially in place, or "in-situ," and assists in converting the asbestos to a non-asbestos material. When the ACM is used as an insulating material, the asbestos fibers may be covered in gypsum that may be at least partially removed or dissolved away. The polycarboxylic acid may (1) directly attack the asbestos and/or (2) dissolve gypsum and form sulfuric acid capable of attacking the asbestos. Additional sulfuric acid may be introduced to assist in conversion of the asbestos to a non-asbestos form. Magnesium sulfate may be introduced to maintain the structural stability of the treated material thereby allowing it to substantially remain in place. Alternatively, the treated material may be safely removed for disposal.
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Page/Page column 8-11
(2008/06/13)
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- Structural and zeolitic features of a series of heterometallic supramolecular porous architectures based on tetrahedral {M(C2O 4)4}4- primary building units
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The utilization of tetrahedral pre-formed coordination compounds {M(C 2O4)4}4- (M = ZrIV, UIV; C2O42- = oxalate) permitted the efficient construction of rare examples of heteronuclear supramolecular nano-porous architectures. A series of metal-organic coordination frameworks prepared by association of these building units with either Mn2+, Cd2+, or Mg2+ have been structurally characterized and are described. Their 3-D chemical scaffold is based on the primary tetrahedral building unit but their pore sizes and topologies could be varied through the M2+ metal ion involved in the assembling process, and the anionic tetrahedral moiety. These structures display channels with apertures up to 12 A × 8 A which are emptied of solvates at mild temperatures without affecting the chemical scaffold, the integrity of which is maintained up to 250-300°C. A certain degree of flexibility of the coordination polymers upon guest release is suggested by the temperature dependence of the powder X-ray patterns and N2 sorption experiments, but reversible and selective sorption of small molecules has been observed substantiating that these open-frameworks behave like sponges. The Royal Society of Chemistry 2005.
- Imaz, Inhar,Bravic, Georges,Sutter, Jean-Pascal
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p. 2681 - 2687
(2007/10/03)
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