Solar-light-driven CO2 reduction by methane on Pt nanocrystals partially embedded in mesoporous CeO2 nanorods with high light-to-fuel efficiency

Abstract

A unique nanocomposite of Pt nanocrystals partially embedded in mesoporous CeO₂ nanorods was prepared by a facile method. The nanocomposite exhibits highly efficient catalytic activity and very good durability for CO₂ reduction by methane (CRM) under focused solar light. It produces very high fuel production rates of H₂ and CO (5.7, 6.0 mmol min⁻¹ g⁻¹) with a very high light-to-fuel efficiency (η, 10.3%). Remarkably, even under the visible-infrared irradiation with wavelengths above 690 nm, it still exhibits efficient catalytic activity with a very high η (10.6%). Based on experimental evidence we demonstrate that the highly efficient catalytic activity arises from a novel efficient solar-light-driven thermocatalytic process of CRM on the nanocomposite. We find a synergetic effect between Pt nanoparticles as catalytically active sites and CeO₂ in Pt/CeO₂-MNR that significantly improves the catalytic activity and durability. We provide an insight into the synergetic effect based on the evidence of in situ FTIR and isotope labeling: the partial confinement of Pt nanocrystals in mesoporous CeO₂ in Pt/CeO₂-MNR makes the oxygen of CeO₂ at the Pt/CeO₂ interface more active due to the metal–support interaction. The active oxygen of CeO₂ at the Pt/CeO₂ interface not only directly participates in the dissociation of CH₄ and the oxidation of the formed CH_x species on CeO₂, but also migrates through the reverse oxygen spillover to the surface of Pt nanoparticles and participates in the dissociation of CH₄ and the oxidation of the formed CH_x species on Pt nanoparticles. On the other hand, both the oxygen vacancies in ceria at the Pt/CeO₂ interface formed by the oxidation of the CH_x species and the Pt sites on the surface of Pt nanoparticles participate in the dissociation of CO₂. Meanwhile, the chemisorbed oxygen on the surface of Pt nanoparticles formed by the dissociation of CO₂ migrates through the oxygen spillover to ceria, where it replenishes the formed oxygen vacancies and participates in the oxidation of the CH_x species on CeO₂. The synergetic effect significantly improves the catalytic activity of Pt/CeO₂ and inhibits the carbon deposition, thus considerably improving the durability.