Probing PhotocatalyticReduction Pathways of CO₂ by Catalyst PbBiO₂Br Using In-Situ Raman Spectroscopy

PbBiO₂Br is an emerging semiconductor material with great potential for visible light driven photocatalysis of CO₂ reduction. <i>In-situ</i> Raman spectroscopy combined with density functional theory (DFT) calculations was employed to clarify the reaction mechanism of CO₂ reduction on PbBiO₂Br. By varying the excitation light intensity and using the activated catalyst, we observed the emergence of intermediates. In total, vibrational bands of seven key intermediates were identified as follows: the C–O stretch of H*COH at the Raman band of 1266 cm^–1; the asymmetric stretch of OC–O in *O*CO^– at 1548 cm^–1; the CO stretch of bridge*CO at 1980 cm^–1; the CO stretch of atop*CO at 2059 cm^–1; the CO stretch of OC*C*O at 2115 cm^–1; the C–H stretch of O*CCHO at 2644 cm^–1; and several bands in the 2786–2901 cm^–1 range, attributed to C–H stretches of alkyl groups. This study provides the spectroscopic evidence of H*COH intermediate formation. Under our experimental conditions, more H*COH than the other reactive intermediate, H*C*O, likely accumulated on the catalyst surfaces and thus had a higher probability of being detected. Methane was the primary product, and small amounts of C_n hydrocarbons were detected by gas chromatography. The Raman spectra confirmed some C₂ intermediates, such as OC*C*O and O*CCHO. The DFT simulations showed the active catalytic sites on the PbBiO₂Br surface to be associated with surface oxygen atoms binding to the carbon sites of adsorbates, resulting in more favorable production of hydrocarbons than of alcohols.