Enhanced methanol-to-olefin catalysis with hierarchical ZSM-5@SAPO-34 composite derived from magadiite

Abstract

We synthesized hierarchical ZSM-5@SAPO-34 (Z@S) composites using magadiite as a silicon precursor to enhance methanol-to-olefins catalysis. The process involves incorporating ZSM-5, with its nanosheet-aggregated spherical structure, into a SAPO-34 precursor gel. By adjusting crystallization times and seed loading, an optimized composite structure was achieved. Powder X-ray diffraction (PXRD) confirms the presence of highly crystalline SAPO-34 and ZSM-5 phases in the Z@S composite. SEM images shows that the composite is not merely a mechanical mixture but involves secondary crystallization of SAPO-34 on ZSM-5 surfaces, with ZSM-5 acting as both the seed and silica source. N₂ adsorption-desorption tests demonstrates that the Z@S composite has a larger specific surface area and micropore volume compared to SAPO-34, ZSM-5, or physical mixed Z@S-PM. Temperature-programmed desorption of ammonia (NH₃-TPD) analysis indicates superior acid strength and a higher density of acid sites in the Z@S composites, contributing to their enhanced catalytic efficacy. We then compared the catalytic performance of SAPO-34, ZSM-5, Z@S-PM, and Z@S. The Z@S composite, featuring hierarchical structure of interconnected mesopores and micropores, promotes efficient diffusion and transport of reactants and products. This result in enhanced resistance to coking within 71 h and 60.0 % selectivity for ethylene and propylene.