CO2 hydrogenation to linear α-olefins on FeCx/ZnO catalysts: Effects of surface oxygen vacancies

Abstract

Selective formation of hydrocarbons from CO2 hydrogenation via the FTS pathway has been attracting interest. Oxygen vacancies (Ov) on the catalyst surface show a subtle role during CO2 activation. Herein, the effects of Ov on FeCx/ZnO catalysts are presented for CO2 hydrogenation to linear α-olefins (LAOs). ZnO with surface Ov of varied concentrations was firstly obtained using heated H2-treatment and used to support active FeCx phases. FeCx/ZnO with appropriate surface Ov achieved CO2 conv. of 48.86% with LAOs sel. of 49.38% and C1 product below 10%. Characterizations confirmed that the Ov concentration exhibited a positive correlation with the interaction between the iron species and ZnO. With H2-treatment of ZnO at 500–600 °C, FeCx/ZnO-T showed 26–33% Ov in all the oxygen species, which increased the surface C/H ratio and promoted the formation of the key intermediate HCOO− and CHx species for chain growth. Excessive Ov accelerated secondary hydrogenation and increased CH4.