Site-Specific Molecular Engineering Redirects Radical Pathways for Selective Photocatalytic Coupling of Methane to...

Toward carbon neutrality, multi-carbon synthesis from photo-driven oxidative coupling of CH₄ (POCM) remains a formidable challenge due to the activity-selectivity trade-off, originating from sluggish surface reaction kinetics and uncontrolled reactive radical reactions. Herein, alkyl thiols (C₉SH) were site‑specifically grafted onto Au sites supported on planar TiO₂, forming the archetypal C₉S-Au^δ+/Au/TiO₂ system featuring covalent gold-thiolate interplay. Combined experimental and theoretical analyses revealed that covalent Au-thiolate interaction could modulate the interfacial electronic structure and upshift the d‑band center of Au sites, thereby strengthening *CH₃ adsorption and lowering the C─C coupling barrier, thus suppressing the ·O₂ ^--driven overoxidation. Moreover, the reconstructed C₉S-Au^δ+ sites acted as rapid electron extraction channels, drawing electrons from adjacent Au nanoparticles and preserving long-lived photogenerated holes for C─H activation. Meanwhile, the alkyl chains served as "molecular fences", effectively promoting local CH₄ enrichment and stabilizing *CH₃ intermediates. The optimized C₉S-Au^δ+/Au/TiO₂ photocatalyst exhibited an excellent yield of 22.92 mmol g_cat ^-1 h^-1 for C₂₊ products with 93.9% selectivity, ranking it among the state-of-the-art noble-metal-loaded photocatalysts for POCM. This work establishes site-specific molecular engineering as an effective strategy to regulate interfacial charge redistribution and redirect radical coupling pathways, enabling CH₄ conversion to multi-carbon products with enhanced activity and selectivity simultaneously.