High-Rate and Selective C₂H₆-to-C₂H₄ Photodehydrogenation Enabled by Partially Oxidized Pd^δ+ Species Anchored on ZnO Nanosheets under Mild Conditions

Abstract

Photocatalytic C 2 H 6 -to-C 2 H 4 conversion is very promising, yet it remains a long-lasting challenge due to the high C−H bond dissociation energy of 420 kJ mol −1 . Herein, partially oxidized Pd δ+ species anchored on ZnO nanosheets are designed to weaken the C−H bond by the electron interaction between Pd δ+ species and H atoms, with efforts to achieve high-rate and selective C 2 H 6 -to-C 2 H 4 conversion. X-ray photoelectron spectra, Bader charge calculations, and electronic localization function demonstrate the presence of partially oxidized Pd δ+ sites, while quasi-in situ X-ray photoelectron spectra disclose the Pd δ+ sites initially adopt and then donate the photoexcited electrons for C 2 H 6 dehydrogenation. In situ electron paramagnetic resonance spectra, in situ Fourier transform infrared spectra, and trapping agent experiments verify C 2 H 6 initially converts to CH 3 CH 2 OH via •OH radicals, then dehydroxylates to CH 3 CH 2 • and finally to C 2 H 4 , accompanied by H 2 production. Density-functional theory calculations elucidate that loading Pd site can lengthen the C−H bond of C 2 H 6 from 1.10 to 1.12 Å, which favors the C−H bond breakage, affirmed by a lowered energy barrier of 0.04 eV. As a result, the optimized 5.87% Pd−ZnO nanosheets achieve a high C 2 H 4 yield of 16.32 mmol g −1 with a 94.83% selectivity as well as a H 2 yield of 14.49 mmol g −1 from C 2 H 6 dehydrogenation in 4 h, outperforming all the previously reported photocatalysts under similar conditions.