Dennis E. Walsh

Constraints on Carbon Formation in Zeolite Catalysts

With the substantial progress in zeolite synthesis techniques and in structure elucidation has come the possibility of systematically comparing catalytic properties across a range of zeolite structures. Of the numerous possible variables, pore structure and pore size were identified as key factors determining not just selectivity in hydrocarbon conversion but also coking tendencies and aging rates. The evidence is reviewed to show that coke formation is a spatially demanding reaction directly controlled by zeolite pore structure but influenced significantly by preferential adsorption. Although the origin of a “carbon” deposit is predominantly controlled by framework structure, the hydrogen/ carbon ratio of that deposit is strongly dependent on the zeolite aluminum content, suggesting a continuing sequence of reactions involving “coke” even after its deposition within a zeolite framework.