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

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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%.