Regulation of CuFeZn catalysts by K3PO4 and its effect on CO2 hydrogenation to C2+ alcohols

Abstract

CO2 hydrogenation to C2+OH is an effective way to diminish CO2 emissions. Although challenges still exist in large-scale applications, CuFeZn catalysts attract extensive attention due to their low-cost. Herein, CuFeZn catalysts are modified by different amounts of K3PO4, (KP)0.1CuFeZn exhibits an excellent catalytic performance (total alcohols selectivity of 15.76 % at CO2 conversion of 38.10 %, C2+OH/ROH fraction of 94.23 %, and C2+ alcohols space–time-yield (STY) of 53.81 mg·mL−1·h−1). Combined with a series of characterization results, it is found that the effect of K3PO4 is complex, and the proportion of Fe2+, Cu0 and medium base shows perfect linear relation to STY of C2+OH. The significance level of the above three factors is in the following sequence: Cu0＞Fe2+＞medium base. The introduction of K3PO4 decreases the proportion of Fe2+ (active site for RWGS, the competitive reaction for C–C coupling) and increases the proportion of Cu+/(Cu++Cu0) (Cu+ is the active site for C–C coupling) due to the synergistic effect of Cu0 and Cu+, thereby improving the synthesis of C2+OH. Moreover, conversion of Fe0 to Fe3C or Fe3O4 plays negative roles in the stability of the catalysts.