Comparative studies of ethanol to propylene over HZSM-5/SAPO-34 catalysts prepared by hydrothermal synthesis and physical mixture

HZSM-5/SAPO-34 catalysts were prepared by physical mixture (named as ZS(m)-MM-n) and hydrothermal synthesis (named as ZS(m)-HS-n), respectively. Ethanol to propylene over these as-prepared catalysts was investigated under different reaction conditions. In addition, the physicochemical properties of these catalysts were characterized by AAS, XRD, N2 isothermal adsorption–desorption, SEM, NH3-TPD and TPO. The catalytic reactivity of HZSM-5/SAPO-34 catalyst was strongly dependent on its preparation method and composition as well as the reaction conditions. ZS(25)-MM-4 (HZSM-5/SAPO-34 = 4, weight ratio; HZSM-5 with Si/Al2 = 25 molar ratio) in isothermal fixed-bed reactor showed the highest propylene yield of ca. 34.5% among these catalysts and the poor catalytic stability. The use of nonisothermal fixed-bed reactor with the temperature configuration (2) significantly improved the catalytic stability of ZS(25)-MM-4. Synergetic effect of HZSM-5 with SAPO-34 occurred in HZSM-5/SAPO-34 catalyst, which modified its properties and catalytic reactivity. The concentration and the strength distribution of acid sites were closely relative to the catalytic reactivity of HZSM-5/SAPO-34 catalyst. For achieving the high yield of propylene, it was necessary that HZSM-5/SAPO-34 catalyst had the moderate concentration and strength distribution of acid sites.