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 cataly tic activities decreased in the order: KX > NaX > HX, in accordance with th e trend of catalyst basic strength. The product selectivities of 3-hydroxyb utanal, butanal and benzene increased with increasing catalyst basic streng th, whereas the reverse trend was found for those of ethylene oxide, propan e and dihydrofurans. The reaction network and associated mechanisms are pro posed and discussed. The main pathway was self-condensation of acetaldehyde to 3-hydroxybutanal, followed by dehydration to 2-butenal. Other side reac tions include isomerization, reduction, cyclodehydration and sequential cro ss-condensation-cyclodehydration. The kinetic parameters for acetaldehyde r eactions over NaX zeolite were estimated. (C) 2000 Elsevier Science B.V. Al l rights reserved.