Mechanism for Heterogeneously Catalyzed Sugar Alcohol Reactions: Hierarchical Modeling and Experimental Studies

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Abstract Title: Molecular-level simulations of the chemistry of hydrogen generation from alcohols in aqueous solutions Recent drivers of sustainability and environmental impact have led to processes for converting plant-derived chemicals into useful products for energy and specialty chemicals. In many cases, the technologies used to convert these compounds rely on expensive catalysts. For example, hydrogen for use as a pollutant-free fuel can be produced from plant-derived alcohols using catalysts comprised of platinum, palladium, rhodium, and other noble metals. The high costs of these catalyst materials percolate into the alcohol conversion costs, limiting the economic viability of these plant-derived raw materials, as well as their competitiveness with conventional petroleum-derived chemicals. Theoretically, less expensive conversion catalysts could be designed. One of the major challenges to finding good catalysts arises from the aqueous phase reaction environment used to process these plant-derived raw materials. These dense, aqueous environments significantly increase the number of molecules that are involved at the molecular level, making it difficult to evaluate their precise roles. This award is to Professors Rachel Getman and David Bruce of Clemson University to utilize a hierarchy of molecular simulation techniques as well as experiments to identify specific ways that water influences molecular-level chemistry for hydrogen production from methanol and glycerol, which are available byproducts of biofuel production. This study will also serve as an excellent training platform for undergraduate and graduate students, exposing them to computational and experimental techniques, and empowering them to intelligently address future scientific and societal problems. Web-based videos and presentations will enable a wider audience to follow the progress of the project and learn about key research findings. Future work will be aimed at designing less expensive catalysts for methanol and glycerol conversions as well as other solution-phase transformations. Many catalyzed reactions occur in the liquid phase, and understanding molecular-level phenomena in liquids is at the forefront of catalysis research. Few fundamental reaction studies have explored how an aqueous solvent environment impacts the entropic and enthalpic driving forces involved in heterogeneous catalysis. To acquire the insight needed to optimize aqueous reaction systems, the objectives of this project are to elucidate the molecular-level mechanisms of two important aqueous phase reactions, specifically methanol oxidation and glycerol reforming, which are currently carried out over heterogeneous catalysts containing platinum and other noble metals (similar to many other reactions involved in biomass processing). This project employs a hierarchy of molecular-level modeling and experiments to identify the most prominent steps in the methanol oxidation and glycerol reforming mechanisms. Quantum mechanics, statistical mechanics, Monte Carlo, and molecular dynamics will be used to model how the aqueous environment influences catalytic phenomena. Ultimately, quantum data and detailed microkinetic models will identify overall product selectivities, and simulation results will be compared with experimental observations for both validation and model improvement purposes. This research is potentially transformative in that it will elucidate adsorbate-intermediate interactions, adsorbate-fluid interactions, and their coupling, thus, providing a complete analysis of catalytic mechanisms in the liquid phase, and facilitating future work in catalyst design for a vital class of liquid phase reactions.