Photocatalytic nonoxidative coupling of methane to ethylene over carbon-doped ZnO/Au catalysts

Abstract

A photocatalytic nonoxidative coupling of methane to multi-carbon compounds remains a huge challenge due to its high dissociation energy of C-H bonds and sluggish charge carrier dynamics. Au-modified carbon-doped ZnO (C-ZnO/Au) photocatalyst is constructed by an interfacial modification-assisted self-assembly approach for efficient photocatalytic nonoxidative coupling of methane to ethylene and hydrogen (2CH₄ = C₂H₄ + 2H₂). Benefitting from the presence of C-ZnO/Au interfaces, the catalyst not only weakens the excitonic confinement to improve the photogenerated charge carrier separation, but also enhances the stability of lattice oxygen to suppress C₂H₄ overoxidation. Moreover, this hybrid catalyst also accelerates the generation of Zn⁺-O⁻ pairs to activate C-H bonds, stabilizes the important reaction intermediate (*OCH₃) to achieve the C-C coupling, and promotes the generation of low-valence Zn to accelerate the dehydrogenation of the *OC₂H₅ into C₂H₄. Therefore, a stable photocatalytic methane conversion performance can be achieved over C-ZnO/Au heterojunctions with a stoichiometric generation of the oxidation product (C₂H₄, 45.85 µmol g⁻¹ h⁻¹) and reduction product (H₂, 88.07 µmol g⁻¹ h⁻¹). This work provides deep insights into the elemental doping and oxide/Au interfaces for the enhanced photocatalytic activity and product selectivity under mild conditions in the absence of extra oxidants.