In Situ Generated Asymmetric Charge‐Polarized Pdδ−‐Oδ−‐Zn Sites for Highly Selective Photocatalytic Oxidation of Methane to Formaldehyde

Abstract

Direct conversion of CH4 into liquid oxygenates remains a great challenge due to the inert C─H bond and the difficulty in achieving unity selectivity toward C1 liquid oxygenates. Current photocatalytic systems mainly focus on C─H activation, while the continuous conversion of oxygenated intermediates toward desired products is rarely addressed. Herein, we propose a mechanism mediated by electronically asymmetric and polarized interfacial Pd‐O‐Zn sites (Pdδ−‐Oδ−‐Zn) that inhibit the reverse hydrogenation of methoxy (*OCH3) intermediates, thereby enabling highly efficient direct conversion of CH4 to HCHO. In situ spectroscopic characterizations combined with DFT calculations uncovered that, compared with Pd NPs‐ZnO, the construction of Pdδ−‐Oδ−‐Zn sites significantly lowers the C─H bond activation barrier of CH4 (from 0.08 to −0.1 eV). Meanwhile, the strong Pd d‐O p orbital interactions facilitate CH3OH dehydrogenation to form *OCH3 intermediates. More encouragingly, these Pdδ−‐Oδ−‐Zn sites effectively promote *OCH3 dehydrogenation to HCHO, thereby suppressing the reverse hydrogenation pathway that regenerates CH3OH. As a result, PdZn‐ZnO delivers an excellent HCHO yield of 8320.5 µmol·g−1 h−1 with a selectivity of 91.6% at room temperature. This work provides a novel strategy for the rational design of high‐performance photocatalysts for the highly selective conversion of CH4 into HCHO.