The overall goal of the project is to enable the design of Lewis acid catalysts for conversion of sugars (readily obtained from fermentation of biorenewables) to value-added chemicals. Metal oxide catalysts, such as titanium dioxide and molybdenum oxides, are active for a number of reactions of sugars, but understanding is lacking regarding relationships between the composition and structure of various catalysts and the products they produce. The project will identify the reasons why different catalysts produce different products, and thus facilitate the design of catalysts that are optimized for the production of specific target compounds, including high-value biorenewable products such as ethylene glycol and lactic acid. The project will utilize low-cost catalyst materials that will pave the way to economically viable routes for enabling sustainable production of valuable chemical feedstocks.
Recent work has shown that the relative rates for key isomerization and retro aldol pathways are strongly influenced by the catalyst composition. A combination of surface science experiments on model surfaces, spectroscopic and kinetic studies of high-surface area oxides, and density functional theory calculations will be employed to identify how surface structure and composition affect the rates of individual elementary reaction steps. Specifically, the research will focus on how elementary reactions for sugar conversion are affected by various surface properties, including electronic properties (such as Lewis acid strength and orbital filling) and geometric factors (such as steric hindrance or proximity of cooperative active centers). Isolation of key elementary steps, which include activation or formation of O-H, C-H, C-O, and C-C bonds in carbohydrates, will be enabled by studying the surface reactions of appropriate probe reactants across the research approaches. Experimental surface science studies will provide new information on elementary step barriers and reaction intermediates on different surfaces. Computation will assist in mechanism development, but more importantly will be used to assess how trends in surface intermediate adsorption energies and barriers for their reactions are related to electronic properties. Operando spectroscopy investigations will provide a new understanding of how complexities, such as non-ideal surfaces and the presence of a solvent, perturb the structure and stability of surface intermediates, providing key feedback for refinement of reaction models that will ultimately be used to design improved catalysts. The project will build on the investigators' track record of training graduate and undergraduate students including students from traditionally underrepresented groups. The project will allow both PhD and undergraduate students to participate in rotations among the different laboratories to develop an ability to address the same overall problem from different angles. Community outreach activities include engagement with an Atlanta-area museum and programs for K-12 students.