Nonthermal Plasma-Assisted Catalytic Oxidation of Carbon Monoxide over CuO_x@γ-Al₂O₃: Understanding Plasma Modification of Catalysts and Plasma–Catalyst Synergy

Nonthermal plasma (NTP)-enhanced CO catalytic oxidation over CuO x @γ-Al 2 O 3 was investigated in a coaxial dielectric barrier discharge reactor at ambient temperature under dry and humid conditions. The CO conversion of 100% was obtained at about 600 J/L under dry conditions. CuO x @γ-Al 2 O 3 had a stronger resistance to water in the NTP-catalytic system in comparison to the thermal-catalytic system. The CO conversion kept stable under humid conditions (RH = 80%) within 10 h in plasma mode, whereas the CO conversion decreased by 12% in thermal mode. It is found that the catalyst’s bed temperature inside the NTP reactor at 600 J/L was not high enough to completely oxidize CO into CO 2, suggesting that CO plasma-catalytic oxidation was not dependent only on the thermal activation caused by the plasma-induced heating. In addition, the CuO x @γ-Al 2 O 3 catalysts after plasma exposure for different times were characterized by N 2 adsorption–desorption, X-ray diffraction, scanning electron microscopy–energy-dispersive X-ray, H 2 -TPR, O 2 -TPD, and X-ray photoelectron spectroscopy. The results show that plasma treatment decreased the ratio of Cu + /Cu 2+ and the surface-adsorbed oxygen species of the CuO x @γ-Al 2 O 3 catalyst. On the basis of the characterization of virgin and plasma-treated CuO x @γ-Al 2 O 3 catalysts as well as the catalytic performance tests, a plausible mechanism of plasma-assisted catalysis of CO is discussed. The Eley–Rideal and Mars–van Krevelen mechanism besides the Langmuir–Hinshelwood mechanism may be responsible for enhancing carbon monoxide oxidation in the plasma-catalytic system. This result brings a new insight into utilizing plasma activation to effectively enhance the catalytic performance.