UV and visible light driven H2 photo-production using Nb-doped TiO2: Comparing Pt and Pd co-catalysts

In this work we compare the performance of platinum and palladium co-catalysts supported on Nb-doped titania materials for the photo-generation of hydrogen using methanol as sacrificial agent. Liquid and gas phase processes are considered. The catalysts physico-chemical properties were characterized by a combination of X-ray diffraction, UV-vis and photoluminescence spectroscopies and transmission electron microscopy, and their photocatalytic performance assessed through the analysis of the optical properties, the measurement of the reaction rates and subsequent computation of the true quantum efficiency in both liquid and gas phase reactors. Using Pt and Pd containing catalysts having similar primary noble metal particle size we compare the two co-catalysts performance in terms of the carbon containing product selectivity of the methanol photo-transformation and the overall performance of the materials in the photon to chemical transformation as measured through the true quantum efficiency. The work shows that Pd displays competitive performance with respect to Pt under UV illumination but not under visible light. The physico-chemical analysis of the solids and particularly the measurement of the charge carrier handling and recombination through photoluminescence at several wavelengths indicate the important role played by charge recombination upon UV illumination but also that other phenomena need to be considered under visible illumination to fully explain the photo-catalytic evolution of hydrogen in noble metal containing catalysts. (C) 2017 Elsevier B.V. All rights reserved.