Synergistic effect of Cu and Mo over Cu–Mo–SiO2 catalyst prepared by sol-gel method for high-efficient and stable de-methoxylation of lignin-derived 4-propylguaiacol

Mo-based catalysts are promising candidates for the de-methoxylation reaction in lignin valorization due to their unique behavior toward the cleavage of C–O bonds. However, the catalytic activities of Mo-based catalysts currently are still unsatisfactory and suffer from severe deactivation. Herein, we report a novel approach for the construction of robust Cu-modified Mo–SiO₂ catalysts by sol-gel method through the synergistic effect of Cu and Mo, among which 0.33Cu–Mo–SiO₂-580 with a Cu/Mo molar ratio of 0.33 exhibited the best catalytic performance for the de-methoxylation of lignin-derived 4-propylguaiacol. Remarkably, the space time yield of 4-propylphenol is among the highest value in literature data. The detailed characterizations confirm that the introduction of Cu by sol-gel method leads to the formation of highly dispersed CuMoO₄ on the as-calcined samples, which results in the enhanced interaction between Cu and Mo species and the formation of a large amount of electron-deficient Mo⁰ on the as-reduced catalyst. Mechanistic studies reveal that electron-deficient Mo⁰ on 0.33Cu–Mo–SiO₂-580 will not only enhance the adsorption ability of substrate, but also improve the C–O bond cleavage ability for the de-methoxylation reaction. Meanwhile, the hydrogen spillover effect induced by Cu⁰ is beneficial to the enhancement of the catalytic activity and stability of 0.33Cu–Mo–SiO₂-580 catalyst.