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Mechanism of hierarchical porosity development in MFI zeolites by desilication: the role of aluminium as a pore-directing agent 总被引:2,自引:0,他引:2
Groen JC Peffer LA Moulijn JA Pérez-Ramírez J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(17):4983-4994
The role of the concentration and the nature of aluminium in the creation of hierarchical porosity in both commercial and synthesized MFI zeolites have been investigated through controlled mesoporosity development by desilication in alkaline medium. Framework aluminium controls the process of framework silicon extraction and makes desilication selective towards intracrystalline mesopore formation. An optimal molar Si/Al ratio in the range 25-50 has been identified; this leads to an optimal mesoporosity centred around 10 nm and mesopore surface areas of up to 235 m(2) g(-1) while preserving the intrinsic crystalline and acidic properties. At lower framework Si/Al ratios the relatively high Al content inhibits Si extraction and hardly any mesopores are created, while in highly siliceous ZSM-5 unselective extraction of framework Si induces formation of large pores. The existence of framework Al sites in different T positions that are more or less susceptible to the alkaline treatment, and the occurrence of re-alumination, are tentative explanations for the remarkable behaviour of Al in the desilication process. The presence of substantial extra framework Al, obtained by steam treatment, inhibits Si extraction and related mesopore formation; this is attributed to re-alumination of the extraframework Al species during the alkaline treatment. Removal of extraframework Al species by mild oxalic acid treatment restores susceptibility to desilication, which is accompanied by formation of larger mesopores due to the enhanced Si/Al ratio in the acid-treated zeolite. 相似文献
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Melián-Cabrera I Espinosa S García-Montelongo FJ Kapteijn F Moulijn JA 《Chemical communications (Cambridge, England)》2005,(12):1525-1527
Decomplexation of organic ligands through redox titration has been applied to catalyst synthesis, developing an improved preparation method for Fe-ferrierite (Fe-FER), the catalyst showing excellent performance and durability for N2O decomposition under realistic conditions for nitric acid plants. 相似文献
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Goossens A. Crajé M. W. J. van der Kraan A. M. Zwijnenburg A. Makkee M. Moulijn J. A. Grisel R. J. H. Nieuwenhuys B. E. de Jongh L. J. 《Hyperfine Interactions》2002,139(1-4):59-66
We report on a 197Au Mössbauer study of several types of supported gold catalysts. Differences in particle size show up in the Mössbauer spectra by a change in the relative weight of the spectral contribution of the surface atoms. The presence of ionic gold in active gold catalysts is not observed. The spectra can be interpreted in terms of bulk-like contributions from the inner-core atoms plus contributions from the outermost atoms at the surface of the particles. 相似文献
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H. A. Smits J. A. Moulijn W. Ch. Glasz A. Stankiewicz 《Reaction Kinetics and Catalysis Letters》1997,60(2):351-356
Mixtures of styrene and 1-octene in toluene were hydrogenated over a monolithic Pd catalyst in the three-phase regime. Styrene
was preferably hydrogenated to ethylbenzene, while a major part of the initial quantity of 1-octene was isomerized to internal
olefins. Formation of alkylcyclohexanes was negligible. Observed rates of styrene hydrogenation were high compared to the
values listed in literature. 相似文献
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Z.M. Babar Wan Mohd Azizi Solachuddin JA Ichwan Qamar Uddin Ahmed Abul Kalam Azad Imranul Mawa 《Natural product research》2019,33(15):2266-2270
The current study provides a way of extraction for both active NSO and WSE from Nigella sativa seeds using 98% methanol. About 1?kg of ground seeds was macerated by 1:2.5 w/v (g/mL) for 72?hours. After rotary evaporation and 7 days of continuous drying and chilling at 50 and 4?°C, NSO and WSE were obtained at the same instant. Solubility tests of 24 solvents and 11 thin layer chromatographic analyses while 2, 2-diphenyl-1-picrylhydrazyl free radical scavenging assay of NSO (73.66) , WSE (33.32) and NSO?+?WSE (78.22) against ascorbic acid (IC50?=?4.28?mg/mL) was performed. WSE was found to be highly soluble in water and 5% NaOH exhibiting the same Rf value of 0.95 for EtOH:DMSO (9:1) against the honey. WSE has revealed more than twofold higher anti-oxidant activity than others. Formulation of WSE with Tualang honey may provide better targeted hydrophilic drug delivery systems. 相似文献
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An experimental study of the thermal decomposition of a β‐hydroxy alkene, 3‐methyl‐3‐buten‐1‐ol, in m‐xylene solution, has been carried out at five different temperatures in the range of 513.15–563.15 K. The temperature dependence of the rate constants for the decomposition of this compound in the corresponding Arrhenius equation is given by ln k (s?1) = (25.65 ± 1.52) ? (17,944 ± 814) (kJ·mol?1)·T?1. A computational study has been carried out at the M05–2X/6–31+G(d,p) level of theory to calculate the rate constants and the activation parameters by the classical transition state theory. There is a good agreement between the experimental and calculated rate constants and activation Gibbs energies. The bonding characteristics of reactant, transition state, and products have been investigated by the natural bond orbital analysis, which provides the natural atomic charges and the Wiberg bond indices. Based on the results obtained, the mechanism proposed is a one‐step process proceeding through a six‐membered cyclic transition state, being a concerted and slightly asynchronous process. The results have been compared with those obtained previously by us (Struct Chem 2013, 24, 1811–1816) for the thermal decomposition of 3‐buten‐1‐ol, in m‐xylene solution. We can conclude that in the compound studied in this work, 3‐methyl‐3‐buten‐1‐ol, the effect of substitution at position 3 by a weakly activating CH3 group is the stabilization of the transition state formed in the reaction and therefore a small increase in the rate of thermal decomposition. 相似文献