Pt基催化剂上CO_(2)辅助丙烷脱氢的反应机理

Reaction Mechanism of CO_(2)-Assisted Dehydrogenation of Propane Over Pt-Based Catalysts

Pt基双金属是一种具有发展前景的丙烷脱氢催化剂,CO_(2)在Pt基催化剂上辅助丙烷脱氢的微观反应机理与优势能量路径尚不明确,为此,采用密度泛函理论(DFT)计算研究了Pt(111)表面及Pt3Mn(111)表面上丙烷直接脱氢反应(PDH)及CO_(2)辅助丙烷脱氢反应(CO_(2)-ODH)的反应网络与关键步骤。计算结果表明:CO_(2)的加入可以降低PDH速控步骤的能垒,对于消耗表面H有利,促进了丙烷脱氢反应正向移动,有利于生成丙烯,从而改变了反应路径和反应动力学;CO_(2)在消除积炭反应中的能垒较高,但是Mn的引入有利于CO_(2)消除积炭。此外,第二金属组分Mn的引入,不但有利于产物丙烯脱附,还提高了C—C裂解能垒,从而提高了丙烯的选择性。

Pt-based bimetals are promising catalysts for propane dehydrogenation.The microscopic reaction mechanism and dominant energy pathway of CO_(2)-assisted propane dehydrogenation on Pt-based catalyst are still unclear.Therefore,the density functional theory(DFT)was used to study the reaction networks and key steps of direct dehydrogenation of propane(PDH)and CO_(2)-assisted propane dehydrogenation(CO_(2)-ODH)on Pt(111)and Pt 3Mn(111)surfaces.The calculation results show that the addition of CO_(2) can reduce the energy barrier of rate-limiting step of PDH,which is beneficial to the consumption of surface H species,thus promoting the forward reaction of propane dehydrogenation.This is conducive to the formation of propylene,and further changes the reaction pathway and reaction kinetics.The energy barrier of CO_(2) in elimination of carbon deposition is high,and the introduction of Mn is conducive to the elimination of carbon deposition by CO_(2).In addition,the introduction of the second metal component Mn not only reduces the desorption energy of propylene product,but also increases its C—C cracking barrier,thus improving the selectivity to propylene product.