Applied Catalysis B: Environmental, Vol.239, 555-564, 2018
Novel photoactivation promoted light-driven CO2 reduction by CH4 on Ni/CeO2 nanocomposite with high light-to-fuel efficiency and enhanced stability
The catalytic CO2 reduction by CH4 to synthesize fuels of CO and H-2 (CRM) supplies a prospective technology to address the global warming effect caused by greenhouse gas of CO2. Due to its highly endothermic characteristics, CRM can only proceed at high reaction temperature, resulting in excessive energy consumption and quick catalyst deactivation due to serious carbon. Herein, we report a nanocomposite of Ni/CeO2 that exhibits high catalytic activity and good stability with focalized UV-vis-Infrared (UV-vis-IR) illumination without applying any other heater. It generates high production rates of H-2 and CO (6.53 and 6.27 mmol min(-1) g(-1)), its light-to fuel efficiency (eta) is up to 11.1%. Ni/CeO2 shows efficient catalytic activity with 11.0% of eta even with focalized Vis-IR illumination of wavelengths above 690 nm. Based on the experimental evidences, it is found that the highly effective catalytic performance of Ni/CeO2 under the focalized illumination originates from the efficient light-driven thermocatalytic CRM. It is discovered for the first time that a synergetic effect among Ni nano particles and CeO2 remarkably facilitates the catalytic durability of the Ni/CeO2 nanocomposite. We delve into the origin of the synergetic effect by combining evidences of XRD, TEM, TG-MS, FTIR, and isotope labelling: The lattice oxygen of CeO2 in Ni/CeO2 participates in the oxidation of C* species formed on Ni nanoparticles via the migration at the Ni/CeO2 interface, thus significantly enhancing the catalytic stability due to the inhibition of carbon deposition. It is found that the solar-light-driven thermocatalytic activity of Ni/CeO2 is considerably improved by a novel photoactivation, which is quite different from the conventional photocatalysis on semiconductor photocatalysts. The novel photoactivation is theoretically revealed by DFT calculation: The irradiation obviously decreases the activation energy of the dominant steps of the C and CH oxidations for CRM on metallic Ni, thus considerably improving the catalytic activity of metallic Ni.