Unraveling the structure-activity relationship in bare Ga₂O₃ for propane dehydrogenation: The critical role of crystallite size and phase composition

The non-oxidative propane dehydrogenation (PDH) has emerged as an on-purpose propene manufacture process, and attracted widespread attention. Herein, the effects of crystallite size and phase composition of Ga₂O₃ on the catalytic performance in PDH were investigated. A series of Ga₂O₃ catalysts with three crystalline phases (α, β, and γ) and different crystallite sizes ranging from 7 to 33 nm, were synthesized using precipitation, hydrothermal, and thermal decomposition methods. It is found that the crystallite size is closely related to the phase composition, among them, γ-Ga₂O₃ showed the lowest crystallite size followed by β-Ga₂O₃ and α-Ga₂O₃. In addition, a clear structure-activity relationship based on crystallite size, acid density, and hydroxyl group density for all different Ga₂O₃ is established, the smaller the crystallite size, the higher the activity. Specifically, γ-Ga₂O₃ exhibits the highest activity due to its smaller crystallite size. Moreover, the rate of propene formation for all Ga₂O₃ is positively associated with the density of acid density and hydroxyl group, and the presence of hydroxyl groups contributes to activating the C−H bond by altering the PDH reaction from non-oxidative to oxidative pathway initially proved by in-situ PDH-MS measurements. Although the Ga₂O₃ catalyst deactivates rapidly in propane stream due to coke formation, the initial activity can be restored after air regeneration treatment. The knowledge derived from this work can be applied to further optimize the PDH activity of Ga₂O₃-based catalysts and related C−H bond activation.