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

Abstract

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.