(509a) Mechanistic Investigations of Catalytic Phase Transformations in Copper-Based Nanostructures during Reverse Water Gas Shift Reactions

With increasing human-generated carbon dioxide (CO₂) emissions driving global temperature increases, urgent collective action is imperative. Among various CO₂ reduction methods, the reverse water-gas shift reaction (RWGSR) is pivotal for CO₂ utilization. As a non-fossil pathway, RWGSR provides essential feedstock for key chemical processes such as Fisher-Tropsch (FT), methanol production, and syngas generation.

Utilizing readily available metal-oxide photocatalysts such as Cu₂O nanocatalysts shows potential for CO₂ reduction through the RWGS reaction. Our investigation revealed dynamic changes in the active phases of Cu₂O nanocatalysts. CO₂ consumption peaked at 300 ℃, followed by a decline and a slight rate increase. Across temperatures from 150 ºC to 500 ºC, the catalyst exhibited consistent ~99% selectivity for CO (with residual CH₄). Dynamic transitions of Cu₂O to metallic Cu was confirmed via operando UV-Vis extinction spectroscopy, XRD characterization, and STEM-EDS spectroscopy. Exploiting the optical properties of these photocatalysts, we observed approximately 22 times visible light enhancement in the reaction rate under both dielectric Cu₂O and plasmonic Cu nanocatalysts phases. Notably, the dielectric metal-oxide (Cu₂O) outperformed the plasmonic metal (Cu) at lower temperatures, necessitating an additional 200 ℃ of thermal energy for optimal performance. Our results show that earth-abundant copper-based photocatalysts are promising catalysts (1) for the valorization and conversion of CO₂ into valuable chemicals and fuels, and also (2) for the conversion and storage of solar energy in the form of chemical fuels.