Polyacrylamide-assisted synthesis of hierarchical porous SAPO-34 zeolites with excellent MTO catalytic performance

Abstract

Silicoaluminophosphate zeolite SAPO-34 with a CHA topological structure has been highlighted for its high methanol conversion and excellent selectivity for light olefins in the methanol-to-olefin (MTO) reaction. In this work, hierarchical porous SAPO-34 zeolite with excellent catalytic properties was first prepared by introducing water-soluble polyacrylamide (PAM) hydrogel into the synthesis system of conventional SAPO-34 by using a one-step hydrothermal synthesis method. The effects of PAM concentration and PAM type on the morphology and pore structure of hierarchical SAPO-34 catalysts and the formation mechanism of hierarchically structured zeolites were studied. Compared to conventional microporous SAPO-34, the hierarchically structured SAPO-34 exhibits excellent performance in the MTO reaction with an approximately three times longer catalytic lifetime (740 min) and remarkably improved selectivity for light olefins of up to 87.5%. A butterfly-shaped hierarchical porous SAPO-34 with a micro-meso-macroporous structure was directly synthesized in the presence of polyacrylamide hydrogel. The tri-level hierarchically structured SAPO-34 exhibits long catalytic lifetime and good thermal stability in the MTO reaction. • A hierarchical porous SAPO-34 with a micro-meso-macroporous structure was directly synthesized in the presence of PAM hydrogel. • The morphology and pore structure of SAPO-34 crystals could be controlled by adjusting the PAM amount and PAM type. • The hierarchically structured SAPO-34 exhibits long catalytic lifetime and good thermal stability in the MTO reaction.