Hydrodeoxygenation of vanillin to 2-methoxy-4-methylphenol over in-situ reduced CuO/Al2O3 catalysts under mild conditions

A new method for the hydrodeoxygenation of vanillin to 2-methoxy-4-methylphenol (MMP) by in-situ reduced CuO/Al2O3 catalysts was developed. The CuO/Al2O3 catalysts with different CuO contents were prepared by simple wet impregnation and could provide complete vanillin conversion with 99 % MMP selectivity under mild conditions (120 °C, 0.5 MPa H2, 8 h). The results from XPS and H2-TPR characterizations of the CuO/Al2O3 catalysts suggested that CuO species had a strong interaction with the Al2O3 support, which was beneficial for the in-situ reduction of CuO to Cu+ and Cu0 species during the hydrodeoxygenation reaction. The synergistic effect of Cu+ and Cu0 species was believed to promote the hydrodeoxygenation of vanillin, in which Cu0 accounts for the hydrogenation reaction, while Cu+ is responsible for the adsorption of vanillin and 4-hydroxy-3-methoxybenzyl alcohol to facilitate the further dehydration of 4-hydroxy-3-methoxybenzyl alcohol. In addition, the CuO/Al2O3 catalyst could maintain high catalytic activity after three reaction cycles and showed versatility for various lignin derivatives. The development of this in-situ reduceable catalyst could provide a cost-effective approach for the upgrading of biomass derived products.