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

Abstract

PbBiO2Br is an emerging semiconductor material with great potential for visible light driven photocatalysis of CO2 reduction. In-situ 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 Cn 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.