The effect of reactor geometry on the photocatalytic reduction of CO2 employing ZnS-MMT (ZnS nanoparticles deposited on MMT) suspension was studied in two annular batch photoreactors. Reaction products in liquid phase (methanol) and in gas phase (methane, carbon monoxide, oxygen and hydrogen) were analyzed by GC/TCD/FID. The dependence of products yields on the reactor diameter and on the volume of the liquid phase confirmed the fact that the requirement of perfect mixing is difficult to fulfill in the annular configuration of the reactor. The highest yields of the photocatalytic reduction were achieved in a configuration where the lamp just touches the surface of the liquid in the reactor and the configuration of the reactor was not annular. (C) 2011 Elsevier B.V. All rights reserved.