Efficient hydrodeoxygenation of guaiacol to phenol over Ru/Ti–SiO2 catalysts: the significance of defect-rich TiOx species

Abstract

Selective hydrodeoxygenation of lignin-derived phenolics to value-added aromatic products such as phenol with high efficiency and low energy consumption remains an important challenge in the field of biomass conversion. Herein, we fabricated a series of Ti-modified SiO₂ supported catalysts (Ru/Ti–SiO₂) with rich Ti³⁺ defects and size-controllable Ru particles via a facile wet impregnation method for the conversion of guaiacol in an aqueous phase. Under relatively mild conditions (240 °C and 0.4 MPa H₂), Ru/Ti–SiO₂ exhibited higher activity for C–O bond cleavage compared with both Ru/SiO₂ and Ru/TiO₂ catalysts, and achieved high guaiacol conversion (83.6%) and phenol selectivity (70.4%). The catalytic activity was increased with the introduction of the Ti modifier, and the deoxygenation ability of the Ru/Ti–SiO₂ catalyst gradually increased with the Ti content. The presence of Ti–O–Si linkages in the Ti-modified SiO₂ support promoted the formation of defect-rich TiO_x species, which further inhibited the aggregation of Ru particles and increased their dispersion, regardless of the high reduction temperature and high Ru loading. Besides, those small-sized TiO_x interacted with Ru electronically and promoted the formation of Ru⁰ species. The interface between Ru and TiO_x species (Ru⁰–Ti³⁺) of the Ru/Ti–SiO₂ catalyst was confirmed as the main active sites for the deoxygenation of guaiacol, benefiting the activation of the C–O bond.