Vapor phase reactions of acetaldehyde over type X zeolites

Vapor phase reactions of acetaldehyde over X zeolites were studied at 1 atm and 300-400 degrees C using a fixed-bed, integral-flow reactor. The catalytic activities decreased in the order: KX > NaX > HX, in accordance with the trend of catalyst basic strength. The product selectivities of 3-hydroxybutanal, butanal and benzene increased with increasing catalyst basic strength, whereas the reverse trend was found for those of ethylene oxide, propane and dihydrofurans. The reaction network and associated mechanisms are proposed and discussed. The main pathway was self-condensation of acetaldehyde to 3-hydroxybutanal, followed by dehydration to 2-butenal. Other side reactions include isomerization, reduction, cyclodehydration and sequential cross-condensation-cyclodehydration. The kinetic parameters for acetaldehyde reactions over NaX zeolite were estimated. (C) 2000 Elsevier Science B.V. All rights reserved.