Pd-Modified ZnO–Au Enabling Alkoxy Intermediates Formation and Dehydrogenation for Photocatalytic Conversion of Methane to Ethylene

Abstract

Photocatalysis provides an intriguing approach for the conversion of methane to multicarbon (C 2+ ) compounds under mild conditions; however, with methyl radicals as the sole reaction intermediate, the current C 2+ products are dominated by ethane, with a negligible selectivity toward ethylene, which, as a key chemical feedstock, possesses higher added value than ethane. Herein, we report a direct photocatalytic methane-to-ethylene conversion pathway involving the formation and dehydrogenation of alkoxy (i.e., methoxy and ethoxy) intermediates over a Pd-modified ZnO−Au hybrid catalyst. On the basis of various in situ characterizations, it is revealed that the Pd-induced dehydrogenation capability of the catalyst holds the key to turning on the pathway. During the reaction, methane molecules are first dissociated into methoxy on the surface of ZnO under the assistance of Pd. Then these methoxy intermediates are further dehydrogenated and coupled with methyl radical into ethoxy, which can be subsequently converted into ethylene through dehydrogenation. As a result, the optimized ZnO−AuPd hybrid with atomically dispersed Pd sites in the Au lattice achieves a methane conversion of 536.0 μmol g −1 with a C 2+ compound selectivity of 96.0% (39.7% C 2 H 4 and 54.9% C 2 H 6 in total produced C 2+ compounds) after 8 h of light irradiation. This work provides fresh insight into the methane conversion pathway under mild conditions and highlights the significance of dehydrogenation for enhanced photocatalytic activity and unsaturated hydrocarbon product selectivity.

Defect Engineering in Photocatalytic Methane Conversion

“…[ 26 ] Furthermore, the adsorption configuration of methane molecules on the surface of photocatalyst can be rationally modulated by regulating the parameters of defects, which is highly beneficial for efficiently converting methane into desired products. [ 27 ]…”

Photocatalytic Conversion of Methane: Recent Advancements and Prospects

“…In arecent breakthrough, Jiang et al discovered that ah ybrid of aZ nO base and Pd single atom modified Au nanoparticles (AuPd-ZnO) facilitates the formation of C 2 H 4 by ap hotocatalytic NOCM. [79] Theo ptimal AuPd 2.7 % -ZnO catalyst achieves amethane conversion of 67 mmol g À1 h À1 with as electivity of 39.7 %a nd 54.9 %f or C 2 H 6 and C 2 H 4 , respectively.D uring the photocatalytic process,m ethane first adsorbs onto the ZnO and dissociates into CCH…”

“…Av ariety of excellent studies focus on the promoted activities of plasmonic metal/semiconductors hybrids in the photocatalytic conversion of CH 4 . [17,29,30,37,45,[76][77][78][79][80] Li et al achieved the plasmon-induced photocatalytic coupling of methane and carbon dioxide to ethene over ah ybrid of Ag nanoparticles and TiO 2 . [80] Irradiation of the Ag nanoparticles by visible light leads to the generation of hot electrons and holes as ar esult of the strong LSPR effect.…”

Methane Conversion Under Mild Conditions Using Semiconductors and Metal-Semiconductors as Heterogeneous Photocatalysts: State of the Art and Challenges

“…As a result, a methane conversion of 536 μmol g −1 and a C 2 + compounds selectivity of 96% (39.7% C 2 H 4 and 54.9% C 2 H 6 in total produced C 2 + compounds) was obtained using the optimized AuPd 2.7% /ZnO photocatalyst after 8 h of irradiaton. Based on in situ characterizations, it was revealed that methane molecules were first dissociated into methoxy on the surface of ZnO under the assistance of Pd and the methoxy intermediates were further dehydrogenated and coupled with methyl radical into ethoxy, which were subsequently converted into ethylene through dehydrogenation ( Jiang et al, 2021 ).…”