Oxidation Chemistry on Transition-Metal Doped Rare Earth Oxide Surfaces: Factors Determining Selectivity for the Oxidative Coupling of Methane

过渡金属掺杂稀土氧化物表面上的氧化化学——决定甲烷氧化偶联选择性的因素。佛罗里达大学的杰森·韦弗和海伦娜·哈格林-韦弗正在研究过渡金属掺杂剂如何改变稀土氧化物（REOs）催化的氧化化学反应，尤其关注碳氢化合物的氧化。特别令人感兴趣的是使用金属掺杂的REOs作为催化剂，有效地促进甲烷（OCM）氧化偶联成有价二碳（C2）产物，同时避免甲烷完全氧化成二氧化碳（CO2）和水（H2O）。开发一种商业上可行的OCM催化剂可以更有效地利用天然气资源，从而产生重大的经济和环境影响。该项目旨在提高对REO催化剂在部分氧化反应和完全氧化反应中的选择性的基本认识，并为设计具有理想和可调性能的金属掺杂REO催化剂提供合理的方法。通过掺杂不同类型的过渡金属来可预测地改变氧化物的催化性能的能力，可以为广泛应用的工程催化剂提供显著的灵活性，包括化学合成，污染控制和能源技术。该项目包括与德国和瑞典的研究人员合作，为研究生提供在国外实验室培训和在同步加速器设备上进行实验的机会。本科生也参与了这项研究，通过调查人员参与大学少数民族指导计划和女性工程师协会，招募了未被充分代表的少数民族。在这个由化学催化项目资助的项目中，dr。佛罗里达大学的杰森·韦弗和海伦娜·哈格林-韦弗正在研究模型稀土氧化物（REO）薄膜和高表面积催化剂的特性，特别侧重于系统地表征过渡金属掺杂对REO表面促进的氧化化学的影响。REOs在多种化学转化中表现出良好的催化性能，包括部分氧化和完全氧化反应。然而，除了铈外，REO表面化学的机理细节和决定催化选择性的因素仅在有限的程度上得到了解。该项目侧重于分别将撒玛利亚和terbia作为有效不可还原和可还原reo的代表性例子，并澄清促进甲烷（OCM）与C2产物氧化偶联而不是完全氧化的因素。采用了一种结合的方法，包括在超高真空（UHV）中对过渡金属掺杂REO薄膜进行模型研究，以及在更现实的反应条件下对纳米晶REO催化剂进行表征，目的是在理解材料和压力差异方面建立清晰的桥梁。该项目的主要目标是对掺杂不同金属的REO表面的结构/电子性质与化学选择性之间的关系有新的认识，并阐明在现实条件下表面化学的机理方面。该项目包括与德国和瑞典的研究人员合作，并为学生提供在国外实验室进行培训和在同步加速器设备上进行实验的机会。本科生也参与了这项研究，通过PI和共同PI参与大学少数民族指导计划和女性工程师协会，招募了代表性不足的少数民族。

Oxidation Chemistry on Transition-Metal Doped Rare Earth Oxide Surfaces - Factors Determining Selectivity for the Oxidative Coupling of MethaneIn this project, Drs. Jason Weaver and Helena Hagelin-Weaver at the University of Florida are investigating how transition-metal dopants modify the oxidation chemistry catalyzed by rare earth oxides (REOs), focusing particularly on the oxidation of hydrocarbons. Of particular interest is the use of metal-doped REOs as catalysts to efficiently promote the oxidative coupling of methane (OCM) to valuable two carbon (C2) products, while avoiding the complete oxidation of methane to carbon dioxide (CO2) and water (H2O). Developing a commercially viable OCM catalyst may enable the more effective utilization of natural gas resources, and thus have significant economic and environmental impacts. The project aims to advance the basic understanding of the selectivity of REO catalysts toward partial vs. complete oxidation reactions, and to enable rational approaches for designing metal-doped REO catalysts with desirable and adjustable properties. The ability to predictably modify the catalytic properties of an oxide by doping with different types of transition metals could afford significant flexibility in engineering catalysts for a wide-range of applications, including chemical synthesis, pollution control, and energy technologies. The project includes collaboration with researchers in Germany and Sweden that provide opportunities for graduate students to train in foreign laboratories and perform experiments at synchrotron facilities. Undergraduate students are also involved in this research, and underrepresented minorities are recruited through the investigators' participation in the University Minority Mentoring Program and in the Society of Women Engineers.In this project funded by the Chemical Catalysis Program, Drs. Jason Weaver and Helena Hagelin-Weaver at the University of Florida are investigating the properties of model rare earth oxide (REO) thin films and high surface-area catalysts, focusing particularly on systematically characterizing the effects that transition-metal doping have on the oxidation chemistry promoted by REO surfaces. REOs exhibit favorable catalytic performance for a diverse set of chemical transformations, including both partial and complete oxidation reactions. However, with ceria as a general exception, mechanistic details of REO surface chemistry and the factors determining catalytic selectivity are understood only to a limited extent. The project focuses on samaria and terbia as representative examples of effectively irreducible and reducible REOs, respectively, and on clarifying factors that promote the oxidative coupling of methane (OCM) to C2 products rather than complete oxidation. A combined approach is employed that involves model studies of transition-metal doped REO thin films in ultrahigh vacuum (UHV) and characterization of nano-crystalline REO catalysts under more realistic reactive conditions, with the aim to establish clear bridges in understanding across the materials and pressure divides. Key goals of the project are to develop new understanding of the relations between structural/electronic properties and the chemical selectivity of REO surfaces doped with different metals and to illuminate mechanistic aspects of the surface chemistry under realistic conditions. The project involves collaboration with researchers in Germany and Sweden and provides opportunities for students to train in the foreign laboratories and perform experiments at synchrotron facilities. Undergraduate students are also involved in this research, and underrepresented minorities are recruited through the PI's and co-PI's participation in the University Minority Mentoring Program and in the Society of Women Engineers.