Origin of Photocatalytic Activity in Continuous Gas Phase CO2 Reduction over Pt/TiO2

The dynamic nature of continuous photocatalytic reduction of gaseous CO2 in the presence of water vapor was studied by using Pt/TiO2 as catalyst under UV irradiation at 353 and 423K in the absence of sacrificial electron donors. The reaction was studied with a good time resolution (order of seconds), to monitor product concentrations by means of mass spectrometry. Two distinct photocatalytic activities, namely steady-state and transient, were identified. The former is active at the lower temperature and only for H-2 production, whereas the latter dominates for CH4 production. The transient activity was recovered during dark time (i.e., the light is off) in the reaction mixture, with the magnitude of recovery proportionally increasing with the duration of the dark time. Higher temperature was found to be more effective for the recovery. Furthermore, insights into deactivation and reactivation mechanisms are explained by insitu diffuse reflectance infrared Fourier transform spectroscopy study.