Direct Spectroscopic Comparison of CO Adsorption over CuOx Prepared In Situ

Copper-based catalysts are widely applied in catalytic CO conversion. Despite their importance in determining catalytic performance, the interaction of CO with different copper states has often been the subject of debate. Herein, we discuss the preparation of four different CuOx states (namely, fully oxidized and reduced (O-573 and R-573, respectively) and 800 and 1000 K annealed (A-800 and A-1000, respectively)) through in situ treatments, comparing CO adsorption behaviors with vacuum-transmission IR spectroscopy. CO only weakly adsorbed on the A-1000 and R-573 surfaces, whereas it led to the creation of trace amounts of surface oxygen vacancies over the O-573 surface, providing adsorption sites for the subsequent CO. Meanwhile, the produced CO2 re-adsorbed on the catalyst to form carbonate species. The reduction process was notably promoted over A-800 due to the presence of abundant surface oxygen vacancies, demonstrating the key role of Cuδ+ in oxygen vacancies, rather than merely its chemical state, in dominating the interaction of CO with CuOx.