Crystal Phase-Dependent Ga-H Chemistry and H ₂ Roles in Ga ₂ O ₃ -Catalyzed Propane Dehydrogenation Reaction

Roles of H₂ in the oxide-catalyzed propane dehydrogenation reaction (PDH) are interesting. Here we report phase-dependent H₂ roles in the Ga₂O₃-catalyzed PDH reaction, in which H₂ co-feeding suppresses the PDH reaction catalyzed by α-Ga₂O₃ with an unchanged apparent activation energy and a negative reaction order against H₂ but promotes the PDH reaction catalyzed by β-Ga₂O₃ with a decreased apparent activation energy and a positive reaction order against H₂. The Ga-H hydride species formed by H₂ activation on α-Ga₂O₃ is much more stable than that on β-Ga₂O₃. During the PDH reaction with co-fed H₂ at 500 °C, the irreversibly adsorbed Gaα-Ga2O3-H species is inert toward C₃H₈ activation and blocks the active site to decrease the C₃H₈ conversion but meanwhile promotes the C₃H₆ desorption to increase the TOF, whereas the reversibly adsorbed Gaβ-Ga2O3-H species reactively activates C₃H₈ at a decreased barrier to promote the PDH reaction via the formation of the more active dynamically cycled Gaβ-Ga2O3-H active site.