Synergistic effect of Ni-Co alloying on hydrodeoxygenation of guaiacol over Ni-Co/Al2O3 catalysts

The hydrodeoxygenation (HDO) of guaiacol was investigated in a batch reactor using Ni-Co/γ-Al2O3 catalysts prepared by co-impregnation method. The structural and physicochemical properties of the catalysts were investigated using BET, XRD, H2-TPR, FT-IR, and NH3-TPD. The characterization results revealed that the formation of various Ni-Co composite species strongly depend on the Ni/Co mole ratio, total metal loadings, and the calcination/reduction temperature. The 6.1Ni3.05CoAl (Ni/Co = 1:2) catalyst seeds the formation of NiCo2O4 spinel structure and subsequent formation of Ni-Co alloy, which represents as specific active site for direct demethoxylation/deoxygenation reaction. The synergistic interaction of Ni-Co enhances the selectivity of benzene. The benzene selectivity of 35.2 % and cyclohexane selectivity of 59.1 % with complete conversion of guaiacol (98.9 %) were achieved with the 3.05Ni6.1CoAl catalyst at 575 K. A tentative reaction pathway is proposed based on the product distribution accomplished during HDO reaction. The structural property was correlated with activity to explore the mechanistic insights.