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 mu mol 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 mu mol g-catal.(-1) h(-1))>TiO2-monolith (43 mu mol g-catal.(-1) h(-1))>TiO2-SS cell (5.2 mu mol 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. (C) 2013 Elsevier B.V. All rights reserved.