Effect of oxygen vacancies on the plasma-catalytic performance of CeO2 for CO2 hydrogenation

While plasma catalysis is a promising approach for sustainable chemical transformations, the fundamental mechanisms governing plasma–catalyst interactions remain elusive. In particular, the role of surface defects, such as oxygen vacancies (OVs) in metal oxide catalysts, on plasma-catalytic CO2 hydrogenation is a subject of ongoing debate. To address this, we synthesized CeO₂ with varying surface OV concentrations through four pretreatment methods: (i) air calcination, (ii) Ar annealing, (iii) air calcination followed by in-situ reduction in H2/Ar plasma, and (iv) air calcination followed by thermal H2 reduction. These catalysts were evaluated in a temperature-controlled packed bed dielectric barrier discharge (DBD) reactor to isolate the impact of surface defects on plasma-catalytic CO2 hydrogenation. Samples with higher OV concentrations exhibited lower CO2 conversion, despite the conventional view that OVs promote CO₂ activation via a (reverse) Mars van Krevelen mechanism. We attribute this inhibition to a significant reduction in the number and intensity of microdischarges. This shift is likely due to a decreased work function of CeO2 following OV formation, which alters the plasma characteristics. In this regime, the modification of the alter the dominant gas phase chemistry appears to overshadow the expected surface catalytic effects. The introduction of Cu nanoparticles on CeO2 further decreases CO2 conversion, a result that correlates directly with a drop in the number and intensity of microdischarges. These findings highlight the critical role of discharge-catalyst interactions in plasma catalysis, which is impacted by the OV concentration on CeO2.