Abstract: Light illumination has been widely used to promote activity and selectivity of traditional thermal catalysts. Nevertheless, the role of light irradiation during catalytic reactions is not well understood. In this work, Pt/Al₂O₃ prepared by wet impregnation was used for photothermal CO₂ hydrogenation, and it showed a photothermal effect. Hence, operando diffuse reflectance infrared Fourier-transform spectroscopy and density functional theory calculations were conducted on Pt/Al₂O₃ to gain insights into the reaction mechanism. The results indicated that CO desorption from Pt sites including step sites (Pt_step) or/and terrace site (Pt_terrace) is an important step during CO₂ hydrogenation to free the active Pt sites. Notably, visible light illumination and temperature affected the CO desorption in different ways. The calculated adsorption energy of CO on Pt_step and Pt_terrace sites was -1.24 and -1.43 eV, respectively. Hence, CO is more strongly bound to the Pt_step sites. During heating in the dark, CO preferentially desorbs from the Pt_terrace site. However, the additional light irradiation facilitates transfer of CO from the Pt_step to Pt_terrace sites and its subsequent desorption from the Pt_terrace sites, thus promoting the CO₂ hydrogenation.

Key words: CO₂ hydrogenation, Photothermal catalysis, Pt/Al₂O₃ Operando diffuse reflectance infrared, Fourier transform spectroscopy, Density functional theory