Light-Enhanced CO2 Reduction to CH4 using Nonprecious Transition-Metal Catalysts

Photothermal conversion of CO2 is of significant interest due to the potential of using both light and heat from the sun to power the catalytic reaction. Herein, the effect of light with different wavelengths and intensities on nonprecious transition-metal catalysts with photoabsorption abilities was explored for the hydrogenation of CO2 to methane. Illuminating Co-10/CeO2 with blue light (450-460 nm) during the reaction invoked a 116% enhancement in catalyst activity with high selectivity to CH4 (94%) at 300 degrees C. The improvement was assigned to the direct activation of adsorbed reaction intermediates by photogenerated hot electrons on the Co surface. Additionally, the hot electrons may contribute to oxygen vacancy generation in the CeO2 support which acts as localized charge density sites. An improved performance was also obtained for Cu-10/CeO2 under green light (560-570 nm) illumination with a 48% enhancement in CO2 conversion and approximately 100% CO selectivity at 450 degrees C, which was attributed to a localized surface plasmon resonance effect by the Cu nanoparticles. To further elucidate the role of light in boosting catalyst performance, the effect of different metals and supports (Ni-11/CeO2 and Co-10/Al2O3) was examined. The superior performance observed for CeO2-based catalysts was attributed to the intrinsic oxygen vacancies in CeO2. The work demonstrates that catalysts having light absorption characteristics can potentially offset part of the thermal energy requirements of energy intensive reactions.