Photocatalytic conversion of CO2 with H2O is an attractive application that has the potential to mitigate environmental and energy challenges through 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) towards (13CO2+H2O). Multivariate curve resolution analysis applied to operando spectra across numerous cycles of photoactivation and CO2 reaction facilitates the identification of principal chemical species involved in the reaction pathways.

Moreover, specific probe-molecules 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 C-C coupling reaction as key intermediates in methane production from CO2 photocatalytic reduction reaction.