SOx storage and release kinetics for ceria-supported platinum

The SOx storage and release kinetics on CeO2 have been studied by lean SOx adsorption and temperature programmed desorption for different pairwise configurations of individual monolith samples, i.e., Pt/CeO2 + SiO2, Pt/SiO2 + CeO2, CeO2 + Pt/SiO2 and CeO2 + SiO2. In the case of sole ceria, SOx adsorption proceeds both via SO2 and SO3 adsorption although the latter channel is kinetically favored. Hence, the rate of SO2 oxidation is crucial for the overall SOx storage kinetics. It is also found that physical contact between Pt and ceria is important for the storage process. This is attributed to efficient transport routes for SOx (surface diffusion and spill-over processes) and/or specific adsorption sites at the platinum-ceria interface. The main route for SOx release is found to be thermal decomposition where the effect of platinum is minor, although an indirect effect cannot be ruled out. Different mechanistic scenarios for SOx adsorption are discussed, which may serve as a guide for future experiments.