Selective catalytic hydrodeoxygenation of vanillin to 2-Methoxy-4-methyl phenol and 4-Methyl cyclohexanol over Pd/CuFe2O4 and PdNi/CuFe2O4 catalysts

Abstract

The development of a sustainable catalytic process for the hydrodeoxygenation of lignin model compounds to renewable fuels and chemicals is essential to meet the requirement of a fossil-fuel-free modern society. Herein a Pd/CuFe2O4 and bimetallic PdNi/CuFe2O4 catalysts were developed for the hydrodeoxygenation of vanillin to 2-methoxy-4-methylphenol (MMP) and 4-methyl cyclohexanol (4-MC), respectively. The Pd/CuFe2O4 provided selective catalytic transfer hydrodeoxygenation of vanillin to MMP with isopropanol (IPA). The synergistic participation of Pd NPs and CuFe2O4 (1Pd/CuFe2O4) afforded 99.4% vanillin conversion and 99.2% MMP selectivity at 150 °C. The acidity of the catalyst facilitated the efficient adsorption of vanillin and IPA, and the high dispersion of Pd NPs lowered the hydrogen abstraction barrier of IPA to facilitate the transformation. Then Ni was incorporated into Pd/CuFe2O4 to produce 4-methyl cyclohexanol from vanillin. The interfacial interaction between Pd and Ni over CuFe2O4 (1Pd7Ni/CuFe2O4) provided 95.8% 4-methyl cyclohexanol (4-MC) in H2 (20 bar) at 180 °C. The acidity of the catalyst, formation of Pd-Ni alloys, and efficient adsorption of vanillin and MMP were responsible for the high activity of the catalyst towards 4-methyl cyclohexanol (4-MC) production. Density functional theory (DFT) calculations were also performed to elucidate the reaction mechanism for vanillin transformation to MMP and 4-MC on the Pd/CuFe2O4 and bimetallic PdNi/CuFe2O4 catalysts.