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Mediating effect of CO2 in base-catalysis by zeolites
Author(s)
Dwyer, John
Date Issued
January 1, 2000
Type
Article
Abstract
Effect 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.
Citation
Studies in Surface Science and Catalysis, 129, 851-858, 2000