Solvent-free synthesis of SAPO-34 nanocrystals with reduced template consumption for methanol-to-olefins process

Abstract

SAPO-34 nanocrystals were synthesized by solvent-free method with significantly reduced template consumption. The obtained SAPO-34 samples were characterized by XRD, SEM, nitrogen adsorption, NMR, NH3-TPD, XPS and XRF. The combination of various Si and Al sources had big impact on the physical-chemical properties of the obtained SAPO-34 crystals, including crystal size, surface area and pore volume, acid strength and distribution and Si environment in the zeolite framework. The nano-sized SAPO-34 crystals exhibited excellent performance in MTO reaction with comparable selectivities to light olefins(combined ∼80% ethylene and propylene selectivity with 50:50 split) and substantially extended catalytic lifetime (from 200min to 840min), compared with micron-sized SAPO-34 catalyst synthesized by conventional hydrothermal method. The extended lifetime could be attributed to the presence of abundant mesopores generated by the stacking of nanocrystals, which alleviated the diffusion constrain and allowed more coke deposition. The unique acid strength and distribution as well as Si environment of the SAPO-34 samples may also contribute to long catalytic lifetime. The solvent-free synthesis method provides a cheap and sustainable way of preparing excellent MTO catalyst with significantly reduced template consumption&waste water emission and improved autoclave efficiency.