Design Of Active Sites On The GaO_x Surface In Propane Dehydrogenation From Density Functional Theory

Propylene is an essential chemical raw material,which can be applied to produce a variety of practical organic chemical intermediates,synthetic resins and fine chemicals.Recently,due to the sharp increase in shale gas production that has reduced the price of light alkanes,the direct dehydrogenation of propane（PDH）to produce propylene on a large scale has sustainable energy and environmental impacts.However,commercial Pt-based and Cr-based catalysts have disadvantages,such as high price and high toxicity.Therefore,there is an urgent need to design catalysts that efficiently activate C-H bonds and maintain high propylene selectivity.Due to the inherent Lewis acidity and basicity of metal oxides,C-H bonds can be selectively activated.Among them,gallium oxide（Ga₂O₃）is a potential catalyst,which has moderate abundance of Ga element and high activity and selectivity in propane dehydrogenation.In addition,the identification of active sites is a necessary prerequisite for improving the catalytic performance.Especially for metal oxide surfaces,the surface structures are dynamically changing during the reaction process,so the construction of a real surface model is extremely complicated and difficult.The research idea of this paper is to find the relationship between the surface characteristic structure and the catalytic performance in the condition of constructing the real metal oxide surface structure under the experimental conditions as much as possible.The density functional theory（DFT）was used to analyze the Ga₂O₃ surface reduced with H₂ and explore the propane dehydrogenation reaction mechanisms.First of all,the construction of surface model in this paper is based on the Ga₂O₃surface reduced with H₂,which contains different active structures including oxygen vacancies,Ga-H and Ga O-H species.DFT was conducted to calculate the propane dehydrogenation activity corresponding to different structures and explore the relationship between surface structure and reactivity.Then,the active sites were screened according to the activity and stability.Based on the idea of guiding the design of the catalyst theoretically,the thermodynamic phase diagram was made to obtain the real Ga₂O₃ surface model with different H₂ partial pressures,and then reaction paths were calculated.Compared with the pristine surface and the defective surface,Ga-H site coordinated with two oxygen vacancies has a unique reaction mechanism and excellent reaction performance,which is consistent with the theoretical screening results.Therefore,this paper further explores the active sites on the complex metal oxide surface that cannot be clearly observed due to limited experimental characterization.It provides an idea for the design of active sites on the Ga₂O₃ and other metal oxide surface in the dehydrogenation reaction.