Selective CO2 Photoreduction to CH4 via Pdδ+ -Assisted Hydrodeoxygenation over CeO2 Nanosheets

Abstract

Here, noble-metal-doped two-dimensional metal oxide nanosheets are designed to realize selective CO₂ photoreduction to CH₄ . As a prototype, Pd-doped CeO₂ nanosheets are fabricated, where the active sites of Pd^δ+ (2<δ<4) and Ce³⁺ -O_v are revealed by quasi in situ X-ray photoelectron spectra and in situ electron paramagnetic resonance spectra. Moreover, in situ Fourier-transform infrared spectra of D₂ O photodissociation and desorption verify the existence of the Pd-OD bond, implying that Pd^δ+ sites can participate in water oxidation to deliver H* species for facilitating the protonation of the intermediates. Furthermore, theoretical calculations suggest the Pd doping could regulate the formation energy barrier of the key intermediates CO* and CH₃ O*, thus making CO₂ reduction to CH₄ become the favorable process. Accordingly, Pd-doped CeO₂ nanosheets achieve nearly 100 % CH₄ selectivity of CO₂ photoreduction, with the raising CH₄ evolution rate of 41.6 μmol g^-1 h^-1 .

Keywords: Carbon Dioxide Photoreduction; Energy Barrier; Noble-Metal Doping; Water Activation.