Selective conversion of furfural to cyclopentanone or cyclopentanol using different preparation methods of Cu–Co catalysts

Abstract

Cu–Co catalysts, prepared by a co-precipitation method (CP) and an oxalate sol–gel method (OG), can selectively convert furfural (FFA) to cyclopentanone (CPO) or cyclopentanol (CPL), respectively. The conversion of FFA to CPO or CPL by Cu–Co catalysts were studied in aqueous solutions. We found that the product distribution was influenced by the catalyst support, Cu loading, calcination temperature, hydrogen pressure, the number of times the catalyst was reused and the preparation method of the catalyst. The surface morphology, surface area and composition of the catalysts were studied by XRD, XPS, BET, ICP-AES and TEM characterization. We found that there was a strong interaction between Cu and Co. Cu⁰, Cu₂O and Co⁰ were the main active catalyst phases on the surfaces of the catalysts, but the amounts were different in the different catalysts. Cu⁰, Co⁰ and Cu₂O were the active hydrogenation species, and Cu₂O also played the role of an electrophile or Lewis acid to polarize the CO bond via lone pair electrons on the oxygen atom. According to XRD and XPS, the main phases on the surface of the CP catalysts were Cu⁰ and Cu₂O. The hydrogenation activity of the CP catalyst was relatively weak and the main product was CPO. In contrast, the hydrogenation activity of the OG catalyst was high and the main product was the fully hydrogenated product CPL due to the main active phases of Co⁰ and Cu₂O on the surface of the OG catalyst. At lower hydrogen pressure (2 MPa) and lower Cu loadings (2% for OG, 5% for CP), we obtained the highest yield of 67% CPO and 68% CPL, respectively.