Regulation of sol-gel derived Cu-M/Al2O3 by metal additives for the selective catalytic transfer hydrogenation of furfural

Furfural is an indispensable platform compound derived from biomass resource and can be hydrogenated to produce a series of high value-added chemicals. In order to overcome the disadvantages of low selectivity and poor stability during furfural hydrogenation, design of promising Cu catalysts with well-disentangled catalytic theory becomes a hot topic. In this work, a series of Cu-M/Al₂O₃ (M=Fe, Co, Ni, Ce) catalysts were prepared by sol-gel method to make a uniform ternary metal composition. Distinctive product distribution for the catalytic transfer hydrogenation of furfural was obtained depending on the specific Cu-M/Al₂O₃ system. Among them, the Cu-Fe/Al₂O₃ displayed superior selectivity of 2-methylfuran compared to any other catalysts. The introduced metal additive acted as the electron donor to regulate the surface dispersion of Cu species. Higher percentage of surface Cu⁰+Cu⁺ species were formed on Cu-Ce/Al₂O₃ and Cu-Fe/Al₂O₃, accounting for the much lower activation energy and better dissociation ability for isoproponal. If Cu-Ni/Al₂O₃ or Cu-Ce/Al₂O₃ was used as the catalyst, hydrogenation happened on the furan ring. Whilst Cu-Co/Al₂O₃ was more preferentially used to produce 2-pentanol and 2-pentanone, with large amount of copper species in oxidative states. The yield of 2-MF reached 84 % at 220 ºC in N₂ at ordinary pressure by Cu-Fe/Al₂O₃ with the specific rate of 106.8 mmol_FAL·g_Cu⁻¹·h⁻¹.