Synthesis of hierarchical SAPO-34 to improve the catalytic performance of bifunctional catalysts for syngas-to-olefins reactions

Zihui Wang

Abstract:

Bifunctional process integrating methanol synthesis and methanol-to-olefins conversion provides a new
synthetic strategy for lower olefins (C2AC4 =), whereas designing matchable zeolite components is still
challenging due to the harsh reaction conditions. Here, a hierarchical SAPO-34 zeolite with a
sandglass-like hollow structure is synthesized from an aluminum-rich precursor gel, which provides
an abundance of crystal defects during zeolite crystallization. The bifunctional catalyst obtained by integrating the hierarchical SAPO-34 and ZnOAZrO2 oxide offers a C2AC4 = selectivity of 80% at 25% CO conversion with excellent stability in syngas conversion. We demonstrate that in the presence of high-pressure
hydrogen, a moderate density of acid sites is the prerequisite for obtaining high C2AC4 = selectivity in syngas/methanol conversion, because the olefins are easily hydrogenated into alkanes by excessive Brønsted
acid sites. The hierarchical architecture significantly prolongs the lifetime of bifunctional catalysts, by
facilitating C2AC4 = desorption and slowing down the coking rate.