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

Photocatalytic CO₂ 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 R2 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 CO₂ conversion systems.