Understanding the redox behaviour of PbCrO4 and its application in selective hydrogen combustion

The performance of PbCrO4 during reduction/oxidation cycles has been studied over the temperature range 673-873 K. During thermal treatment in an inert atmosphere, PbCrO4 is stable up to 773 K. At higher temperatures, it decomposes rapidly and irreversibly to Pb2(CrO4)O. Moreover, the redox cycling of Pb2(CrO4)O is also irreversible at 873 K when the reduction semi-reaction is prolonged beyond 3 min. Taking a standard 2 min cyclic treatment, we demonstrate that the surface reduction/oxidation of Pb2(CrO4)O is exothermic between 773-873 K. In contrast, the redox cycling of PbCrO4 is endothermic at 673 K. These findings demonstrate for the first time the potential of Pb2(CrO4)O as a solid oxygen reservoir for the oxidative dehydrogenation of alkanes; especially at T ≥ 773 K, where H2 oxidation by Pb2(CrO4)O is exothermic. Preliminary kinetic studies suggest that Pb2(CrO4)O reduction and oxidation both proceed through a "3D diffusion of the reacting front" mechanism. Our results open up opportunities for developing energy-efficient oxidative dehydrogenation routes to commercially important olefins.