The structure dependency of the activity and stability of Pd-phosphide catalysts in propane dehydrogenation

Abstract

A large number of alloy nanoparticle catalysts with novel configurations and compositions have been reported for efficient propane dehydrogenation. Although efforts have been made to rejuvenate the spent catalysts, the recovery of these well-defined active sites is still a daunting challenge. In this work, silica supported palladium-phosphide nanoparticles, with uniform particle sizes (∼2.5 nm) and specific crystal structures were prepared and systematically characterized. The combined structure analysis reveals that the exposed Pd site changes from metal Pd surface to few-atom Pd ensembles and fully isolated Pd atoms with gradually increasing P content. For identical reaction conditions of propane dehydrogenation, both the clustered Pd atoms and isolated Pd^δ+ atoms exhibited dehydrogenation rates that is >10 times higher than the corresponding rate over Pd nanoparticle. Kinetic measurements demonstrated that the clustered Pd atoms on the surface of Pd₃P nanoparticle shows the highest activity for C–H activation, while its also favored by coke deposition, leading to a trade-off relationship between activity and stability. By contrast, the Pd atoms on PdP₂ surface exhibited a compromised dehydrogenation performance. Based on the deactivation mechanism of Pd-phosphide catalyst during dehydrogenation/regeneration cycles, an effective regeneration method, washing catalyst bed with alkaline-ethanol under mild conditions, was developed to remove deposited coke around dehydrogenation sites without sintering of nanoparticles. The structure–activity/stability relationship insights and facile regeneration method for the binary catalysts in this work offer improved knowledge of propane dehydrogenation catalyst.