Operando DRIFTS Investigations on Surface Intermediates and Effects of Potassium in CO₂ Hydrogenation over a K-Fe/YZrO_x Catalyst

A detailed operando DRIFTS study on the CO2 Fischer-Tropsch reaction with K-promoted Fe/YZrOx catalysts was performed to investigate the influence of this modification on the catalytic performance in the formation of lower olefins as well as higher hydrocarbons and to gain insights into mechanistic aspects. Catalytic testing revealed an enhanced formation of olefins and hydrocarbons by adding potassium to the catalysts, while spectroscopic studies revealed various stable adsorbates and intermediates such as monodentate carbonates, bicarbonates, formates, formyl, and methoxy on the surface of the K-promoted Fe/YZrOx catalysts compared to the unpromoted one. Based on gas-feed switching experiments and statistical analysis of literature IR data regarding Fe-containing catalysts, it was found that carbonate species interacting with H2 are transformed to higher hydrocarbons and methane via formate and formyl formation, while bicarbonate species are decomposed accompanied by the formation of CO, which then further reacts to form formate or formyl and finally hydrocarbons.