Transient In situ DRIFTS Investigation of CO2 Hydrogenation to Methanol over Unsupported CuGa Catalysts

Abstract Gallium oxide‐based catalysts are promising candidates for CO 2 hydrogenation to methanol, whilst mechanistic understanding of the catalytic systems is not yet fully understood. Here, transient in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies of CO 2 hydrogenation over the unsupported CuGa and CuGaN (with N doping) catalysts were conducted. The findings show that N doping could possibly promote the formation of surface Cu + sites on the interface between Cu and Ga 2 O 3 , and hence increasing the selectivity to methanol. However, N doping prohibited the reduction of Ga 2 O 3 to oxygen‐deficient Ga 2 O 3‐ x , which is unfavorable for CO 2 conversion. Additionally, during DRIFTS the steady‐state isotope transient kinetic analysis (SSITKA) was performed (under H 2 /D 2 isotopic switching conditions). The SSITKA results confirm that the Cu + ‐bound formates were likely the key intermediates for methanol synthesis over the catalyst, and the N doping could also weak the interaction between CO* species and the catalyst surface, and thus facilitating the selectivity towards methanol rather than CO. Findings of the work show that the partial nitridation of the metal oxides could be the strategy to promote methanol synthesis selectivity.