The promoting effect of Nb on Ni/SiO2 in the hydrodeoxygenation of lignin derivatives to cycloalkanes†

Effective non-noble metal catalysts are critical for upgrading lignin-derived compounds into valuable products by hydrodeoxygenation (HDO). In this study, new Ni⁰–NiNbO_x/SiO₂ catalysts were synthesized by combining sol–gel and impregnation methods. The HDO performance of these catalysts was then evaluated in the production of cycloalkanes from lignin-derived phenolic compounds. These Ni⁰–NiNbO_x/SiO₂ catalysts present a considerably larger specific surface area than their Ni/SiO₂ counterparts. They work as bifunctional catalysts in the HDO process, where Ni⁰ species act as active sites for hydrogenation while NiNbO_x provides the Lewis acid sites necessary for deoxygenation. In this way, a significant improvement in the cyclohexane yield from 18% to 94.4% in guaiacol HDO was achieved on these Ni⁰–NiNbO_x/SiO₂ catalysts. The best catalyst 10Ni/20Nb@SiO₂ exhibits complete conversion of guaiacol and almost 100% selectivity of cycloalkanes at 250 °C. The apparent activation energy for the 10Ni/20Nb@SiO₂ catalyst was identified to be 54.2 kJ mol⁻¹, notably lower than that for other reported Ni-based catalysts. These findings highlight the superior performance of Ni⁰–NiNbO_x/SiO₂ catalysts in the HDO of lignin-derived phenolic compounds, underscoring their great potential in producing cycloalkanes from renewable resources. Our efforts help pave the way for the catalytic transformation of lignin into valuable biofuels to advance the global mission toward a sustainable supply of fuels.