Balancing C–O Bond Activation and Hydrogen Spillover at Cu–Mo Oxide–Sulfide Interfaces for Selective Demethoxylation of Lignin-Derived Guaiacols

Selective demethoxylation of lignin-derived guaiacols requires sufficient interfacial hydrogen for CAr–OCH3 bond cleavage, whereas excess hydrogen promotes aromatic-ring hydrogenation and deep deoxygenation. Controlled sulfurization of Cu-promoted molybdenum oxide created nanoscale oxide–sulfide interfaces that balance target-bond activation with hydrogen delivery. Optimization of Cu/Mo ratio and sulfur content afforded Cu0.5-Mo-S0.1, which achieved 95.4% conversion and 97.9% alkylphenol selectivity at 250 °C and 3 MPa H2 while retaining activity over seven cycles. X-ray diffraction (XRD), Raman, and high-resolution transmission electron microscopy (HRTEM) support intimate contact between nanoscale MoO2 and MoS2 domains, while sulfur-induced shifts of Mo X-ray photoelectron spectroscopy (XPS) components to lower binding energies suggest a plausible Mo–O–Mo–S interfacial motif. Bader analysis revealed interfacial charge redistribution consistent with XPS, supporting its electronic plausibility. In situ Fourier transform infrared (FT-IR) spectroscopy, hydrogen-spillover experiment, and density functional theory (DFT) calculation elucidate the interface-mediated reaction mechanism. The Mo–O–Mo–S boundary promotes the vertical adsorption of lignin-derived oxygenates toward the interface, facilitating direct CAr–OCH3 bond cleavage and subsequent hydrogenation of the intermediates, while weakening alkylphenol adsorption to promote product desorption. Meanwhile, Cu–S bonding attenuates hydrogen spillover, thereby suppressing aromatic-ring hydrogenation. Alkylphenol selectivity exceeded 98% across the examined para-alkyl guaiacols. Thus, matching selective C–O activation with moderated interfacial hydrogen supply provides a strategy for selective demethoxylation.