Epitaxial growth of surface-passivated core-shell ferrierite

Abstract

Ferrierite (FER) is both a natural and synthetic zeolite that is commonly utilized as a catalyst in commercial processes that take advantage of its two-dimensional network of micropores. The external surfaces of zeolite crystals often impose deleterious effects on catalyst performance, such as external coking or unselective reactions as a result of unconfined acid sites. One technique that can improve the efficiency of zeolite catalysts is surface passivation wherein the aluminosilicate crystal is encapsulated within a shell of its siliceous isostructure. These core–shell configurations eliminate surface acidity, forcing reactions to occur within interior (confined) pores for improved shape-selectivity while simultaneously reducing rates of deactivation, which extends catalyst lifetime. In this study, we examine whether a Si-rich shell can be epitaxially grown on the surface of an aluminosilicate FER crystal in fluoride-free media. Epitaxial growth of an ultra-thin Si-rich shell was confirmed by multiple characterization techniques showing no evidence of pore blockage or misoriented shell growth during core–shell synthesis. The passivation of external acid sites was confirmed using Friedel-Crafts alkylation of mesitylene and benzyl alcohol as a benchmark reaction for probing surface acidity. Overall, these findings confirm that it is possible to synthesize core–shell ferrierite with an aluminosilicate core and a silicon-rich shell via a facile seed-assisted growth procedure.