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Surface Hydroxyl Network Promoted Hydrogen Transfer Dynamics for Efficient Photocatalytic Acetylene
Menghui Deng1, Zhihan He2, Youyu Pang2
1State Key Laboratory of Solidification Processing and School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an, 710072, P.R. China.
None:
Photocatalytic semi-hydrogenation of acetylene (C2H2) to ethylene (C2H4) is seriously limited by the inefficient generation and directional transfer of active hydrogen species. Here, we report a proton-coupled electron transfer (PCET) mechanism for photocatalytic acetylene semi-hydrogenation by establishing a hydroxyl network over hydroxyl-modified carbon nitride (C3N4-OH)/Ni(OH)2 composite. Such a hydroxyl network not only enhances photogenerated charge separation but also establishes a strong hydrogen-bonding microenvironment for adsorbing interfacial water and facilitating hydrogen transfer dynamics. Femtosecond transient absorption (fs-TA) spectroscopy, in situ photochemical infrared spectroscopy, kinetic isotope effect (KIE), and active hydrogen (H*)-trapping reveal that the fast proton transfer via a PCET mechanism, rather than a conventional hydrogen atom transfer (HAT) pathway. Eventually, the C3N4-Ni(OH)2 achieves an exceptionally high C2H4 production rate of 15.7 mmol gcat -1 h-1 with a C2H4 selectivity of 98.2% under simulated solar irradiation. For purifying a crude C2H4 stream containing 0.5 vol% C2H2, the C2H2 conversion remains ∼98% over a long-term continuous-flow operation. This work elucidates the pivotal role of surface hydroxyl networks in governing hydrogen kinetics and paves a new avenue for the design of high-performance photocatalysts.
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