La-modified nanocrystalline Cu4(NO3)2(OH)6 for highly selective CO2 reduction into CH4 under near-infrared light illumination

Abstract

Photocatalytic CO2 reduction reaction (CO2RR) has drawn tremendous attention for the resource utilization of CO2. However, the selective photoconversion of CO2 to CH4 utilizing near infrared (NIR) light remains a significant challenge. Transition metal hydroxide salts can efficiently harvest NIR light, which still requires further exploitation. Moreover, rare-earth element modification is an attractive strategy for improving the selectivity due to the special electron configurations of rare earths.Herein, a new photocatalyst, La-modified Cu4(NO3)2(OH)6 (La/CuNH) single crystals, was designed and prepared via a facile mechanochemical method. Under λ≥800 nm irradiation, La/CuNH reaches a methane product yield of 2.21 μmol g -1 for 3 h through a fully gas-solid reaction, ca. 4.11 times higher compared to CuNH, which aligns with 100% selectivity. As evidenced by X-ray photoelectron spectra and density functional theory simulations, the La atoms assist the construction of asymmetric Cu-O-La, which induces electron redistribution. The electrons accumulate at the Cu catalytic sites, considerably facilitating CO2 hydrogenation reduction toward targeted CH4 formation. In addition, modifying La atoms on Cu4(NO3)2(OH)6 optimizes the d-band center, which is more conducive to adsorb CO2 and intermediates. Furthermore, the relative hydrophobicity clearly validates the fast mass transfer of CO2 on the surface of La/CuNH. This research paves the way for the development of metal hydroxide salts as photocatalysts and the modulation of selectivity for near-infrared-driven CO2 methanation.