In-situ transformation of a natural Xuyi palygorskite into nano-structured K-Ca-Fe-Mg/SAPO-34 zeolites for enhanced MTO catalytic performance

A nano-structured K-Ca-Fe-Mg/SAPO-34 (MeAPSO-34) composite catalyst was successfully synthesized through the in-situ transformation of palygorskite (Pal) under steam-assisted crystallization conditions. Pal served as a multifunctional precursor, providing inherent Si, Al, Fe, Mg, K, and Ca elements that were directly incorporated into the catalyst framework without the addition of external metal sources. This approach facilitated the formation of hierarchically porous SAPO-34 zeolites with a well-balanced distribution of Brønsted and Lewis acid sites, as confirmed by comprehensive characterization techniques including XRD, SEM, BET, XPS, and NH₃-TPD. Complete methanol conversion was achieved over the MeAPSO-34 zeolite catalyst, with ethylene and propylene selectivities of 69.0 % and 27.4 %, respectively, at a reaction temperature of 410 °C, a methanol-to-water feed ratio of 1:6, and a weight hourly space velocity (WHSV) of 1 h⁻¹. Notably, the synergistic interaction among the K, Ca, Fe, and Mg multi-metallic components significantly promoted the water-gas shift reaction and effectively suppressed coke deposition. Furthermore, the nanostructured morphology of the catalyst reduced the diffusion limitations by shortening the gas-phase transport pathways, thereby enhancing the overall catalytic performance of the SAPO-34 zeolite. This study presents a scalable strategy for designing high-performance methanol-to-olefin (MTO) catalysts through the direct transformation of clay minerals into nanostructured multifunctional materials.