Evidence on C-C Coupling to Acetate as Key Reaction Intermediate in Photocatalytic Reduction of CO₂ over Pt/TiO₂

Photocatalytic conversion of CO₂ with H₂O is an attractive application that has the potential to mitigate environmental and energy challenges through the conversion of CO₂ to hydrocarbon products such as methane. However, the underlying reaction mechanisms remain poorly understood, limiting real progress in this field. In this work, a mechanistic investigation of the CO₂ photocatalytic reduction on Pt/TiO₂ is carried out using an operando FTIR approach, combined with chemometric data processing and isotope exchange of (¹²CO₂ + H₂O) toward (¹³CO₂ + H₂O). Multivariate curve resolution analysis applied to operando spectra across numerous cycles of photoactivation and the CO₂ reaction facilitates the identification of principal chemical species involved in the reaction pathways. Moreover, specific probe-molecule-assisted reactions, including CO and CH₃COOH, elucidate the capacity of selected molecules to undergo methane production under irradiation conditions. Finally, isotopic exchange reveals conclusive evidence regarding the nature of the identified species during CO₂ conversion and points to the significant role of acetates resulting from the C-C coupling reaction as key intermediates in methane production from the CO₂ photocatalytic reduction reaction.