The selective reduction of carbon dioxide (CO2) by H2 into CO and H2O (i.e., reverse water-gas shift reaction, RWGS) is considered as one of the promising approaches for CO2 mitigation and valorization. Among the earth-abundant metal and metal oxide nanocatalysts reported in the literature, cuprous oxide (Cu2O)-based nanocatalysts have emerged as the promising catalysts for RWGS reaction. However, under conventional thermal energy (only)-driven catalytic conditions, Cu2O-based nanocatalysts still require relatively higher operating reaction temperatures. Therefore, there remains a challenge to develop a highly active low-temperature catalyst(s) for RWGS reaction. In this talk, we will show that visible light can be used as a powerful tool to enhance the catalytic activity of copper-based nanocatalysts for the RWGS reaction. This visible light enhancement enables higher reaction rate(s) at relatively lower reaction temperatures on these copper-based nanocatalysts. Our results also show that Cu2O nanocatalysts undergo dynamic changes under the RWGS reaction conditions. Specifically, the catalyst changes from the Cu+ oxidation state into the metallic (Cu0) state. Operando UV-Vis extinction spectroscopy, ex-situ XRD, and STEM with EDS mapping are used to confirm the phase changes of cuprous oxide catalysts under the RWGS reaction conditions. We will also show that greater light enhancement is observed on the functioning Cu2O catalyst in comparison to the Cu catalyst. The visible light enhancement observed on the Cu2O nanocatalyst is due to the dielectric Mie resonances, whereas the rate enhancement observed over the functioning Cu nanocatalyst is due to the plasmonic Mie resonances. The greater light enhancement observed over the functioning Cu2O nanocatalyst is most likely due to the expected longer lifetime of charge carriers (e.g., excited electrons) in the dielectric Cu2O photocatalyst than the lifetime of hot electrons in the plasmonic Cu photocatalyst. Our findings show that the dielectric Mie resonance-enhanced photocatalysis on the metal-oxide (e.g., Cu2O) nanocatalysts has advantages over plasmonic Mie resonance-mediated photocatalysis in the metals (e.g., Cu).

Plasmonic versus dielectric Mie resonance-enhanced photocatalysis: Example of photocatalytic reverse water-gas shift reaction on copper-based nanocatalysts

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