Investigation into the photothermal catalytic CO2 decomposition over CeO2 with different morphologies: Behaviors of oxygen vacancies

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CO2 is a viable renewable energy source, as global CO2 emissions are perennially increasing. The decomposition of CO2 to CO and O2 through high-temperature cracking of metal oxides via a two-step thermochemical cycle has been an effective strategy to reduce CO2 concentrations in the atmosphere. However, this thermochemical cycle requires a high reaction temperature (1273 K). Hence, in this study, we investigated photothermal CO2 decomposition over three CeO2 catalysts with different morphologies: porous CeO2 nanosheets (2D-CeO2), cubic-shaped CeO2 (C-CeO2), and octahedral CeO2 (O-CeO2). The photothermal synergistic effect eliminated the necessity of high temperatures, where light illumination increased the generation of oxygen vacancies and electron transfer to promote CO2 decomposition. The maximum rate of CO production by 2D-CeO2 at 250 °C was 69 μmol g-1h−1, which is significantly higher than those of O-CeO2 (47 μmol g-1h−1) and C-CeO2 (19 μmol g-1h−1). However, no activity was observed in dark conditions, even at 250 °C. In-situ DRIFTS, quasi in-situ EPR, XPS, and Ar-TPD experiments revealed that light irradiation promotes the production of oxygen vacancies on the catalyst surface and generates the intermediate CO2•− species, which cleave the C=O bonds and CO2 conversion, while temperature promotes the adsorption of CO2 on the catalyst surface and facilitates electron transfer. DFT calculations revealed the differences in oxygen vacancy formation and CO2 adsorption among various exposed crystal facets of CeO2. These findings provide new avenues for CO2 decomposition based on the adsorption and activation of CO2 on metal oxide surfaces and the low-temperature synergistic photothermal effect.