Zn and Na promoted Fe catalysts for sustainable production of high-valued olefins by CO2 hydrogenation

Abstract

The direct conversion of CO2 into olefins has stimulated the enthusiasm because of its significant role in reducing CO2 emission and establishing carbon-neutrality society. Here, we report that Na and Zn promoted Fe (Na-Zn-Fe) catalysts show prominent catalytic performances, which provide C2-C12 olefin selectivity of 80% and high-valued C4+ linear α-olefin (LAO) selectivity of 46% at CO2 conversion of 39% in CO2 hydrogenation. The space-time yields (STYs) of C2-C12 olefins and LAOs could be achieved as high as 3.7 and 2.1 g gcat−1 h−1, respectively, which are significantly higher than those reported to date. The structure-performance of Na-Zn-Fe catalysts is well correlated. It is revealed that the addition of Zn into Fe catalysts remarkably reduces the particle size of Fe species, and enhances the H2 adsorption amount, which promote the activity of CO2 hydrogenation. The co-modification by Na promoter increases the CO2 adsorption, facilitates the formation of active Fe5C2 with higher proportion, and thus increases the CO2 conversion. Significantly, Na promoter is enriched on Fe surfaces and improves the olefin selectivity by inhibiting their hydrogenations. It is demonstrated that the reverse water–gas shift (RWGS) step in CO2 hydrogenation over Na-Zn-Fe catalyst is severely impeded by H2O, which formed during CO2 hydrogenation, and would make the CO2 conversion limited to an extent.