Al2O3形貌和GaN电子效应影响VOx催化丙烷氧化脱氢作用机制及动力学研究

The selective oxidative dehydrogenation of propane is an important technique for increasing propylene production. The key problems for the selective oxidative dehydrogenation of propane are easy deep oxidation of the target propylene product and low selectivity of propylene during the reaction process. To solve these problems, the VOx-GaN/Al2O3 catalyst is proposed in this project. The active sites distribution and existing state forms of VOx species over the surface of Al2O3 can be controlled by preparing different morphologies of the Al2O3 supports and adjusting the pore channel structure, morphology and size. The catalytic activity and selectivity for the selective oxidative dehydrogenation of propane are mainly influenced by the active site and mass diffusion of the VOx-GaN/Al2O3 catalyst. The main purpose of this project is to achieve highly dispersed and isolated VOx species V supported catalyst, which may have high activity and selectivity for the targeted reaction. In order to modify the oxidation-reduction properties of VOx reactive species over VOx/Al2O3 catalyst, the GaN semiconductor promoter with fast rate of electron mobility and high thermal conductivity is introduced into VOx/Al2O3 catalyst. The effect of support and promoter on the surface active species and reaction diffusion mechanism of VOx-GaN/Al2O3 catalyst can be revealed through the catalyst characterizations of XRD, UV−Vis DRS, LRS, NMR, XPS, XAFS, NH3−TPD, H2−TPR etc. from atom, molecule and nano level scale and the reaction kinetics of mass diffusion investigation. The catalytic reaction mechanism, catalytic kinetics and mass transfer diffusion for the selective oxidative dehydrogenation of propane can be obtained by combining the experimental and theoretical study, which will provide the information for further designing and developing of VOx-GaN/Al2O3 catalyst having high catalytic performance and fast mass transfer diffusion, and also will help to promote the efficient utilization of low carbon alkane resources and its technical innovations.

丙烯是一种重要的石油化工基本原料，现有技术难以满足市场的需求，丙烷选择性氧化脱氢是丙烯增产的一条重要技术路径。本项目拟针对该过程存在的深度氧化、丙烯选择性低等难题，选择不同形貌的Al2O3作为载体，通过改变载体孔道结构、尺寸和催化剂制备方法，实现对VOx活性物种分散状态的控制；通过引入半导体助剂GaN，利用其电子效应促进VOx的氧化-还原性能，制备高分散、高活性的负载VOx催化剂。从原子、分子和纳米层次构建VOx催化剂多尺度表征方法，结合传质扩散和反应动力学研究，揭示载体和助剂对催化剂表面VOx活性物种的种类/分散状态和反应扩散行为的影响机制。借助实验与理论计算相结合的研究方法，阐明丙烷选择性氧化脱氢制备丙烯的催化反应机理，获得催化反应动力学及传质扩散等信息，为研发具有明确活性位和有利于传质扩散的负载型VOx催化剂提供理论参考依据，该研究将有助于推动低碳烷烃资源化高效利用技术的创新。

丙烯是一种重要的石油化工基本原料，目前主要来自炼油工业中流化催化裂化和石脑油裂解乙烯的联产工艺。然而，石化资源的严重短缺使得该技术难以满足日益增长的市场需求，而丙烷选择性氧化脱氢是丙烯增产的一条重要技术路径。本项目针对该过程存在的深度氧化、丙烯选择性低等难题，选择了SBA-15、MCF、KIT-6\Silicalite-1、Ti‐SBA‐15、Al2O3、SiO2、NaZSM-5等作为载体，通过改变载体的微介孔道结构、尺寸、表面基团数量与分布和催化剂表面活性物种结构和电子性质，实现了催化剂表面GaN或VOx活性物种的种类及分散状态、催化剂表面酸碱性种类、强度及分布的可控调变，获得了高分散、高活性的GaN和VOx负载型催化剂。阐明了载体表面基团−孔道结构/尺寸对GaN 活性物种、晶粒大小、电子效应等影响机制，通过与目标反应性能的关联，获得了催化剂活性物种结构与反应性能的关联性。借助XPS、TPSR、Operando FT−IR 和 UV−Vis DRS等表征技术和DFT理论计算相结合，揭示了载体对催化剂表面活性物种的种类/分散状态和反应扩散行为的影响机制，阐明丙烷/丁烷O2/CO2选择性氧化脱氢制备丙烯/丁烯的催化反应机理，获得了催化反应动力学。通过对比催化剂催化丙烷直接脱氢（DHP）、O2氧化丙烷脱氢（O2-ODHP）和CO2氧化丙烷脱氢（CO2-ODHP）以及TPSR+MS实验发现，CO2可以通过耦合DHP反应和RWGS反应消耗反应中生成的H2，促使反应向生成丙烯方向移动，从而提升了丙烷转化率和丙烯选择性。另外，对反应后催化剂的积炭种类进行分析发现，CO2可以通过Boudouard反应减缓催化剂表面积炭的生成，延长催化剂的使用寿命，进一步阐明了CO2对目标反应的催化作用机制。该研究将有助于推动CO2、低碳烷烃资源化高效利用技术的创新，特别是降低CO2的排放具有潜在的应用价值。