CO2 hydrogenation to lower olefins over Mn2O3-ZnO/SAPO-34 tandem catalysts

Abstract

The direct conversion of CO2 hydrogenation to lower olefins via methanol as an intermediate is of great significance, but challenges still remain. Herein, we present a binary Mn2O3-ZnO oxide, which is responsible for catalytic hydrogenation of CO2 to methanol. After combination of Mn2O3-ZnO and SAPO-34 molecular sieve, the catalytic reaction displays a markable increase. CO2 adsorption by alkaline nature, followed by oxygen vacancy activation and synergistic hydrogenation over the binary Mn2O3-ZnO oxide are the prerequisites for the tandem reaction. However, the tandem spacing between oxide and molecular sieve plays a crucial role, because the suitable intimacy can induce enhanced methanol formation as intermediate via tandem dynamics effect, causing an apparent limitation for reverse water gas shift reaction at high temperature. The optimum mass ratio of 3:1 for two phases demonstrates that more components of binary oxide are needed to improve the rate of CO2 hydrogenation to methanol, aiming to balance the two-step tandem reaction. Finally, under conditions of 380 ℃, 3 MPa and 3600 mL/gcat/h, 20%Mn2O3-ZnO/SAPO-34 tandem catalyst is obtained by physical ball milling after 15 min, with excellent stability, sulfur tolerance and catalytic performance with CO2 conversion at almost 30%, lower olefins selectivity of 80.2% (propylene/ethylene = 5.6:1), and single-pass yield of 10.7%.