Oxygen vacancy-enriched Cu/CeO2–ZrO2 catalyst with highly dispersed Cu0 towards plasma catalytic advanced CO2 utilization

Abstract

Direct conversion of CO2 into CO is an effective way of utilizing atmospheric CO2 to meet the “carbon neutrality” goals set by governments worldwide. However, traditional thermal catalytic CO2 reduction reactions have limited large-scale industrial applications because they typically require temperatures above 500 °C, with virtually no activity at 60 °C. Moreover, high temperatures can cause aggregation of active metal within the catalyst, thereby affecting the catalytic efficiency. In contrast, non-thermal plasma (NTP) can potentially enhance the catalytic system's performance even at 60 °C. Therefore, this study used NTP to enhance the catalytic conversion of CO2 to CO over Cu/CeO2–ZrO2 (Cu/CZO) in a plasma reactor. First, the effects of the catalyst loading and specific input energy of NTP on the CO2 conversion rate were examined. The results showed that at 60 °C, CO2 conversion over 7 wt% Cu/CZO reached a maximum of 37.76%. Subsequently, the gas-phase and surface reactions were decoupled to obtain much needed information about the mechanisms of plasma-enhanced catalytic reactions. The catalysts were characterized using H2-tempreature-programmed desorption (TPD), CO2-TPD, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. In-situ spectroscopy was also employed to investigate the active species generated during NTP reactions. The characterization results confirmed that Cu0 serves as the active site for H2 adsorption, while oxygen vacancies act as the active site for CO2 adsorption. Furthermore, it was established that NTP can selectively enhance these two types of active sites, thereby improving the catalyst's adsorption capacity for reactants and exciting ground state CO2 in the gas phase, resulting in improved reaction performance. Finally, based on the obtained evidence, a mechanism is proposed for Cu/CZO catalytic CO2 conversion enhanced by NTP, providing valuable insights for NTP-enhanced catalytic processes.