Sooknoi, Tawan
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Sooknoi, Tawan
Alternative Name
Sooknoi, T.
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tawan.so@kmitl.ac.th
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Item type:Publication, Mediating effect of CO2 in base-catalysis by zeolites(2000-01-01); Dwyer, JohnEffect of acidic carbon dioxide on alkylation with methanol over basic zeolite catalysts were studied. The catalysts, prepared by ion-exchange NaX zeolites with CsOH solution, were believed to contain excess amount of cesium salts on external surfaces and in the micropores. The alkylations of acetonitrile/toluene with methanol were conducted at 350°C using fixed-bed down flow reactor. Helium was used as carrier gas at atmospheric pressure. Gas chromatography was employed to analyse and quantify the products. Infrared spectroscopy was applied to investigate the adsorption of substrate on the basic sites. It was found that substrate electrophilicity played an important role in the alkylation over basic zeolites. For the alkylation of toluene with methanol, the activity was markedly decreased on application of carbon dioxide into the reactant stream. This is due to the competitive adsorption of acidic carbon dioxide over toluene on basic sites. In contrast, enhanced activity was observed in the reaction of more electrophilicity substrates, acetonitrile. It is suggested, in this work, that acetonitrile possess stronger adsorption strength, as compared to carbon dioxide, and it may well react with carbon dioxide to form an intermediate which is relatively more active in the alkylation with methanol. Together with infrared spectroscopy, there was an evidence that adsorption of substrates on basic sites was the rate determining step and the mechanism for the mediating of carbon dioxide in alkylation of acetonitrile was also suggested to increase reaction activity. © 2000 Elsevier Science B.V. All rights reserved. - 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.