Isoprene Synthesis from Formaldehyde and Isobutylene over Zeolite Catalysts

Abstract: Single-stage gas-phase synthesis of isoprene from formaldehyde and isobutylene in the presence of zeolite catalysts of the MFI, BEA, and FAU(Y) framework types and Al–BEA, Zr–BEA, Sn–BEA, and Nb–BEA catalysts synthesized by isomorphous substitution methods has been studied. Catalytic tests have shown that the isoprene yield increases in the following order: Zr–BEA < Sn–BEA < Nb–BEA < Al–BEA, which is in agreement with the content of Brønsted acid sites in the samples, whereas the formation of the major byproduct—carbon monoxide resulting from the decomposition of formaldehyde—increases with an increase in the number of Lewis acid sites. Comparison of the catalytic properties of zeolites of the different framework types has shown that the highest isoprene selectivity is exhibited by medium-pore MFI zeolites with a pore diameter of 5.5 Å.