A versatile bi-metallic copper–cobalt catalyst for liquid phase hydrogenation of furfural to 2-methylfuran

Abstract

Liquid phase hydrogenation of furfural (FFR) to 2-methyl furan (2-MF) was examined using noble metal free, Cr-free, bi-metallic Cu–Co catalysts. Three supported bi-metallic catalysts (Cu–Co/SiO₂, Cu–Co/H-ZSM-5, and Cu–Co/γ-Al₂O₃) with various Cu/Co molar ratios (x/y = 1, 2, and 4) with fixed Cu loading (x = 10 wt%) were prepared by the impregnation method. The physico-chemical properties of various catalysts were studied by using XRD, N₂-sorption, SEM, TEM, TPR, TPD, XANES/EXAFS and CHNS methods. The results confirmed the formation of spinel CuCo₂O₄ oxides, and much higher dispersion of Cu on acidic supports such as H-ZSM-5 and γ-Al₂O₃. However, the absence of a spinel CuCo₂O₄ oxide was observed in Cu–Co/SiO₂ via XANES/EXAFS results. XRD and TEM results revealed the formation of bigger Cu particles in Cu–Co/SiO₂. In the catalytic activity studies, Cu–Co/γ-Al₂O₃ catalyzed the hydrogenation of furfural with 98.8% conversion, resulting in maximal selectivity of 2-MF due to the presence of maximal Cu-CoO_x sites. The H-ZSM-5 supported catalyst had marginally less 2-MF selectivity, whereas the silica supported catalyst exhibited maximum selectivity towards furfuryl alcohol (FOL) because of the large copper particles. H₂-TPR and EXAFS results revealed that the incorporation of cobalt metal improves the reducibility of Cu-catalysts, thus improving the catalytic activity. Bi-metallic Cu–Co/γ-Al₂O₃ catalysts displayed higher activity as compared to their monometallic counterpart, and Cu–Co/γ-Al₂O₃ (x/y = 1) exhibited the best catalytic performance with 78% selectivity to 2-MF at 220 °C and 4 MPa.