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Item type:Publication, The catalytic conversion of acetonitrile to acrylonitrile in zeolitic systems: Rationalization of experimental observations using theoretical simulations(2007-12-15); Limtrakul, JumrasQuantum mechanical calculations have been performed on faujasite and silicalite models to investigate reported experimental differences in yields of two key catalytic products (propionitrile and acrylonitrile) formed from the reaction of acetonitrile with either methanol or formaldehyde, respectively. The calculations were performed using 12T and 10T cluster representations of faujasite and silicalite, respectively, and the results are in good overall agreement with experimental observations. Both reactions are predicted to proceed in a concerted manner, with the transfer of a proton to the basic zeolite oxygen atom in conjunction with the methyl group migration to form a reaction intermediate. The stationary points found on the reaction surface in both zeolites have been systematically assessed using principal components analysis to give us an insight into the correlated nature of the structural/electronic changes that occur on the reaction surfaces. © 2007 Elsevier B.V. All rights reserved.2 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Role of substrate's electrophilicity in base catalysis by zeolites: Alkylation of acetonitrile with methanol(2004-03-15); Dwyer, JohnThe role of substrate's electrophilicity in base catalysis was studied by competitive adsorption and catalytic alkylation of acetonitrile over basic zeolite catalysts. Methanol was used as alkylating agent, comparing with the side-chain alkylation of toluene. Solid base zeolite catalysts including CsNaX, CsNaY and CsNaEMT were prepared and modified by simple ion exchange and impregnating parent zeolites with caesium salt. Their physical and chemical characteristics were then determined by XRD, SEM and elemental analysis. Adsorption was studied by FTIR using a special in situ adsorption cell. The gas-phase catalytic reaction was carried in a down-flow microreactor and products from the reaction were analysed by on-line TCD-GC. Adsorption strength of the substrates was found to depend largely on their electrophilicity and basicity of the zeolite framework. The strong adsorption of acetonitrile on basic zeolite catalysts also leads to an increased alkylation activity, but reduces the decomposition of methanol to carbon monoxide and hydrogen. In addition to the reaction temperature, the competitive adsorption of acetonitrile and methanol predominantly effects on product selectivity, particularly the unsaturation/saturation ratio. Moreover, the excess caesium "clusters" present in the zeolite framework plays important role in both adsorption and alkylation of the substrates. Further investigation was made on stability of the catalysts and it was found that coke formation is small in base catalysis, as compared to those found in acid zeolites. FTIR reveals that the carbon deposits are composed mainly of high polar products and the catalysts can be readily regenerated without significant loss of catalytic activity. © 2003 Elsevier B.V. All rights reserved.1