Thermal and Photon Effects on H2 and O2 Recombination Kinetics Over a Ag-Pd/Tio2 Catalyst

The recombination reaction of H2 and O2 to water have been studied over Ag-Pd/TiO2-anatase, under dark and photo-irradiation conditions in the gas and liquid phases. The catalyst consisted of metal particles of mean size of ca.1nm dispersed over 10-15nm TiO2 particles. Kinetic parameters including order of reaction (n), rate constant (k), activation energy (Ea) and binding constant (K) were evaluated. Ea for the thermal reaction was found to be 49kJ.mol -1. K values at low initial H2 concentrations are comparable for both gas and slurry phases. However, the value decreased considerably at higher initial H2 concentration in slurry. The overall quantum yield of the reaction in the slurry phase is found to be 0.09. Considering the number of metal particles on TiO2, the yield per particle was found to be 0.16, in the slurry phase. A possible explanation of the changes in kinetics with respect to experimental conditions is given.