Unified light-thermal-diffusion coupling multi-mechanism kinetic model for gas–solid photocatalytic CO2 reduction with experimental and simulation validation

A multi-mechanism kinetic model for CO 2 photocatalysis was developed and validated in a tree-channel reactor, accurately capturing illuminated mass transfer and reaction kinetics, with strong agreement between experiments and simulations. Photocatalytic CO 2 reduction in gas-solid systems is a complex process that requires the integrated consideration of illumination, photocatalytic performance, and gas diffusion on the catalyst surface. Oversimplification of these factors in existing computational fluid dynamics models severely compromises their predictive capability under realistic reaction conditions. To address this limitation, this study develops a multi-mechanism kinetic model that integrates photoexcitation, Arrhenius thermal activation, Langmuir adsorption saturation, and Thiele diffusion resistance within a unified kinetic expression. Model parameters were constrained and validated using a combination of first-principles calculations and multiscale optical, spectroscopic, adsorption, and transport measurements in a tree-shaped uniform-flow reactor. Photocatalytic experiments of four distinct catalysts are then used to validate the multi-mechanism kinetic model, with R 2 above 0.98. Under model-derived conditions, the operation of the tree-shaped reactor achieve an optimal conversion rate of 116.7 μmol g −1 h −1 . The model reliably predicts the experimental rates across a wide range of operating conditions. It also accurately captures the optimal space velocity range and the promotional effect of increasing temperature. This work offers a generalizable framework for the theoretical understanding, modelling, and scale-up of photocatalytic CO 2 conversion systems.