Dual hydrogen-buffer and interfacial spillover effects boosting bimetallic catalysts for mild-condition guaiacol hydrodeoxygenation

Abstract

Regulating hydrogen activation and transport is an effective strategy for improving bimetallic catalyst performance in the hydrodeoxygenation (HDO) of lignin-derived phenolics under mild conditions. Herein, we report a dual hydrogen-regulation strategy that integrates silicotungstic acid (SiW₁₂) with a sequentially Ni–Ru bimetallic catalyst to control hydrogen availability and reaction selectivity in aqueous-phase HDO. Mechanistic investigations combining electrochemical measurements, UV–Vis spectroscopy, in situ DRIFTS, and hydrogen adsorption analysis demonstrate that SiW₁₂ performs a dual function. In solution, it acts as a molecular hydrogen buffer that facilitates hydrogen transfer from the gas–liquid interface into the bulk liquid while mitigating mass-transfer limitations. During reaction, in situ modification of the Ni–Ru/TiO₂ interface by SiW₁₂ generates interfacial sites that promote hydrogen spillover and proton-assisted C–O bond polarization. This cooperative interaction between homogeneous redox buffering and heterogeneous interfacial catalysis establishes a dynamic catalytic environment integrating H₂ activation, hydrogen transport, acid-assisted bond cleavage, and suppression of carbonaceous deposition during aqueous-phase HDO. Noble-metal on Ni/TiO₂ studies (Pt, Ru, Pd) further reveal that hydrogen chemisorption strength and metal–support interactions govern hydrogen mobility and buffering efficiency, resulting in the activity trend Ni–Pt > Ni–Ru > Ni–Pd, while the Ni–Ru configuration provides the optimal balance between hydrogen activation and selective hydrogenation to cyclohexanol. Collectively, under mild conditions (0.5 MPa H₂, 125 °C), the catalyst delivered 59.8% guaiacol conversion and 69.3% cyclohexanol selectivity within 1 h. This work introduces a dynamic hydrogen-management paradigm for one-pot HDO to enable energy-efficient biomass upgrading under mild multiphase reaction conditions.