Influence of Topology and Chemical Composition of MTT and MFI Zeolites on Catalytic Properties in the Isomerization Reaction of Ethylene Oxide to Acetaldehyde

Abstract

It has been shown by the example of zeolites with the MTT (Al-ZSM-23 and Fe-ZSM-23) and MFI (Al-ZSM-5 and Fe-ZSM-5) structures that mesoporous zeolites are efficient catalysts for the gas-phase isomerization of ethylene oxide to acetaldehyde. At 300–400°C and complete conversion of ethylene oxide, the selectivity of its conversion to acetaldehyde (S_AA) reaches at least 90%. The key factors determining the selectivity and stability of the catalyst are the topology of the zeolite and its acid properties. Unidimensional zeolites with the MTT structure demonstrate higher S_AA in comparison with the samples with the three-dimensional MFI structure. Decreasing the strength of Brønsted acid sites by replacing Al by Fe in the zeolites of both structural types also leads to a growth in S_AA. The samples are arranged in following order of decreasing S_AA: Fe-ZSM-23 > Fe-ZSM-5 = ZSM-23 > ZSM-5. The main byproduct of the reaction is crotonic aldehyde, the formation of which is promoted by strong Brønsted acid sites. The crotonic aldehyde selectivity over aluminosilicate samples is above 6%.