Photocatalytic reduction of chromium(VI) with titania powders in a flow system. Kinetics and catalyst activity

The photocatalytic reduction of chromium(VI) with titania powders has been studied using a continuous flow system. The kinetics and the influence of catalyst concentration and pH on the reaction rate have been analyzed. Kinetic results show a half-order reaction at pH lower than 4, and a first-order reaction for pH above 4. Deactivation of titania was found when reduction of chromium(VI) was carried out at pH higher than 4, due to the fouling of titania caused by chromium hydroxides. A model for catalyst deactivation has been developed. It describes the performance of the catalyst at the different experimental conditions tested. Furthermore, the results obtained in the kinetic studies are supported by data from electronic microscopy and adsorption techniques.