Rate-controlling steps in a three-phase (solid—liquid—gas) photoreactor: a phenomenological approach applied to hydrogen photoprodution using PtTiO2 aqueous suspensions

Abstract Water photolysis has been studied using a three-phase solid—liquid—gas photoreactor, continuous with respect to the gas phase. The PtTiO 2 catalytic powders were kept suspended in water by means of gas bubbling through the liquid. In this case, the hydrogen production rate can be controlled by the luminic step and dark (chemical or mass-transfer) steps. The relative importance of each of these steps depends on the lamp-photoreactor system used, the nature and physical characteristics of the photocatalysts, and the operating (fluidodynamic) conditions. A description of the steps involved in this photocatalytic process is given. The importnce of mass transfer in limiting process yield is shown, showing that this step has to be considered in the development of photocatalysts even at early stages.