Enhanced stability and propylene yield in methanol to light olefins conversion over nanostructured SAPO-34/ZSM-5 composite with various SAPO-loadings

Abstract

Nanostructured core-shell silicoaluminophosphate (SAPO)-34/zeolite socony mobil (ZSM)-5 composite has been synthesized with various SAPO-34 loadings in order to control light olefins selectivity and increase its lifetime in methanol to olefins process. Physicochemical properties and catalytic performance of SAPO-34/ZSM-5 composite catalyst were different, compared with the parent SAPO-34 and ZSM-5. As-synthesized samples were characterized by different methods such as X-Ray diffraction, field emission scanning electron microscopy, Brunauer–Emmett–Teller, energy-dispersive X-ray, Fourier transform infrared spectroscopy, and NH 3 -temperature-programmed desorption techniques. By increasing SAPO-34 content in composite catalysts, relative crystallinity of CHA-phase (chabazite) was enhanced, whereas it was decreased for MFI-phase. Also, surface area improved by increasing SAPO-34 loading in core-shell composite catalysts. The results of the activity test showed that lifetime remarkably increased by using composite catalysts. Compared with the parent SAPO-34 and ZSM-5, the composite catalyst with 80% SAPO-34 loading showed higher methanol conversion and olefins selectivity with time on stream. This is due to the synergic effect between SAPO-34 and ZSM-5 zeolites in composite catalyst.