Hydrodeoxygenation of vanillin to creosol under mild conditions over carbon nanospheres supported palladium catalysts: Influence of the carbon defects on surface of catalysts

Abstract

Hydrodeoxygenation (HDO) is a promising process for biomass upgrading. A challenge is designing and developing related efficient catalysts. Here, we developed a defects enhancement engineering to synthesize carbon-based supported Pd catalysts (0.5%Pd/CNS) for vanillin HDO under mild condition. It is found that the degree of carbon defects was negative correlation with the cross-linked degree of resorcinol–formaldehyde (RF) resin sphere (carbon precursor), which can be modulated by amount of ammonium fluoride (NH4F) (0, 0.01, 0.03, and 0.05 g). The RF resin sphere (RF-0.03) with the lowest cross-linked degree was obtained by addition of 0.03 g NH4F, and then 0.5%Pd/CNS-0.03 possessed rich carbon defects obtained by carbonization of RF-0.03. The catalyst possessing the most degree of carbon defects (1.96 of AD1/AG from Raman data, D1 ∼ defective carbon, G ∼ graphitic carbon) exhibited the highest activity among as-prepared catalysts: 100% of vanillin conversion and 100% of yield to creosol in vanillin HDO over 0.5%Pd/CNS-0.03 (0.03 g of NH4F) at 60 °C, 0.1 MPa H2, and 1 h. The excellent performance can be attributed to the rich carbon defects on surface of catalysts, which can play an important role on growth of active metal and activation of reactants. This work improves green catalysis of HDO with a strategy of defect engineering to surface microenvironment modulation.