(544ha) Insights into the Surface Chemical and Catalytic Properties of Photocatalysts That Dictate Activity and Product Distribution in CO2 Photocatalytic Reduction By H2O

Authors: 
Poudyal, S., University of Tennessee
Parker, M., University of Tennessee Knoxville
Laursen, S., University of Tennessee
Despite many decades of diligent research in photocatalysis to achieve a truly sustainable and more environmentally friendly chemicals and fuels, a significant lack of understanding with respect to catalyst electronic properties, surface chemistry, and surface reaction mechanisms that drive CO2 reduction and the selective production of hydrocarbons or oxygenates still persists. Specifically, the role of photocatalyst surface reactivity towards controlling catalytic activity and product distribution remains mostly unexplored. In this study, we utilized a combined experimental and theoretical approach to investigate photocatalytic CO2 reduction by H2O in an organic-free, concentrated solar photoreaction (CSPR) conditions at elevated temperatures (120-350ºC) over a suite of photocatalysts that exhibit a range of surface reactivity towards carbon and oxygen and variable bulk electronic properties. Our results have shed light upon several chemical and physical phenomena at the mechanistic level that drive elementary reaction steps on the surface. Some valuable insights include the isolation of new H-transfer mechanisms and variation in surface chemistry under a range of experimental environments (variable temperature, variable chemical potential of reactants, kinetic isotope effect, etc.). Results indicate that semiconductors with a high Debye temperature (temperature where e-/h+ recombination becomes appreciable), robust bulk bonding, and elevated surface chemical reactivity could directly promote new reaction intermediates produced via thermal/vibrational routes that further enhance the selectivity towards hydrocarbon synthesis. Insights into the role of surface chemistry and the development of new H-transfer mechanisms in photocatalysis that have not been explored previously have enabled the tunability in the selectivity between hydrogenation to produce hydrocarbons and oxygenates versus H2 – a critical efficiency aspect of the system.