Photocatalytic CO₂ reduction and kinetic study over In/TiO ₂ nanoparticles supported microchannel monolith photoreactor

In this study, a microchannel monolith photoreactor was investigated for photocatalytic CO₂ reduction with H₂O in gaseous phase using TiO₂ and indium doped TiO₂ nanoparticles. Effects of operating parameters such as monolith geometry, reaction temperature, indium loading and feed ratios were investigated to maximize yield rates. CO and CH₄ were the main products with maximum yield rates being 962 and 55.40 μmol g-catal.^-1 h^-1, respectively and selectivity being 94.39 and 5.44%, respectively. The performance of the photoreactor for CO production was in the order of In/TiO₂-monolith (962 μmol g-catal.^-1 h^-1) > TiO₂-monolith (43 μmol g-catal.^-1 h^-1) > TiO₂-SS cell (5.2 μmol g-catal.^-1 h^-1). More importantly, the quantum efficiency in microchannel monolith reactor was much higher (0.10%) than that of the cell type reactor (0.0005%) and previously reported internally illuminated monolith reactor (0.012%). The significantly improved quantum efficiency indicated photon energy was efficiently utilized in the microchannel monolith reactor. A simple kinetic model based on Langmuir-Hinshelwood model, developed to incorporate coupled effect of adsorptive photocatalytic reduction and oxidation process, fitted-well with the experimental data.