Synthesis of a phosphomolybdic acid-modified AlPO4-5/SAPO-34 composite catalyst and its catalytic performance in the MTO reaction

Abstract

SAPO-34 catalysts with high selectivity for light olefins were first synthesized via the introduction of phosphomolybdic acid (HPMo) and AlPO4-5 zeolite into the initial gel. The physical and chemical characteristics of the synthesized catalysts were determined by a series of techniques and the catalytic performance of the modified composite zeolites for the methanol-to-olefin (MTO) reaction was investigated. The results indicated that HPMo-modified SAPO-34 was featured with more Brønsted acid sites, more mesopores, and a smaller crystal size, thereby demonstrating superior catalytic performance. The further combination with AlPO4-5 (16.7 wt%) prolonged the lifetime of the HPMo-modified SAPO-34, which is thought in this paper related to its 12-ring straight channel (0.7–0.8 nm) and the absence of any Brønsted acid sites. The MTO tests showed that the light olefins selectivity for the modified composite zeolites reached 95.1 %, while the catalyst lifetime remained at 445 min