High-efficiency catalytic hydrodeoxygenation of lignin-derived vanillin with nickel-supported metal phosphate catalysts

Lignin is a natural and renewable aromatic raw material of aromatic chemicals and its depolymerization and downstream products conversion has drawn considerable attention. Herein, a series of Ni loaded metal phosphates (Ni/MP, M = Ti, Zr, Nb, La, or Ce) catalysts were fabricated for the hydrodeoxygenation (HDO) of lignin-derived vanillin (VAN) to produce 2-methoxy-4-methylphenol (MMP). It has been demonstrated that 97.25% VAN conversion could be obtained with a yield of 88.39% of MMP under the mild condition of 220 °C and 0.5 MPa H2 for 30 min with 15 wt% Ni/ZrP. The highest activity of Ni/ZrP was attributed to its small Ni particle size, large specific surface area, strong metal-support interaction, and optimal acidity. It has been proven that Ni, Lewis acid sites (LAS) and Brønsted acid sites (BAS) have a synergistic effect in VAN conversion: Nano-sized Ni catalyze the dissociation of H2 to form active hydrogen species (H[rad]). LAS promote the adsorption and activation of VAN and isopropanol. BAS play a vital role in the dehydration reaction. Additionally, H2 was the primary hydrogen donor in the system, while isopropanol was the reaction medium as well as the secondary hydrogen donor, helping to reduce the external H2 supply requirement. By optimizing the reaction conditions and studying the promotion mechanism, we hope to provide an experimental basis for lignin catalytic hydrogenolysis.