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

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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.