Selective liquid-phase hydrogenation of furfural to furfuryl alcohol over Cu-based catalysts

• Cu catalysts free of Cr are active in the selective liquid-phase furfural hydrogenation.
• Small metal copper particles are more active for furfural hydrogenation than large ones.
• Interaction of small Cu0 particles with a Mg-Al spinel-like boosts hydrogenation rate.
• Mg-Al spinel phase provides additional active sites for activating furfural CO group.

In this work, the liquid-phase furfural hydrogenation over different Cu-based catalysts was studied. The catalysts were prepared by incipient wetness impregnation (Cu/SiO2-I), precipitation–deposition (Cu/SiO2-PD) and co-precipitation (CuMgAl, CuZnAl and Cu-Cr) methods. CuMgAl, CuZnAl and Cu/SiO2-PD showed higher Cu dispersion and H2 chemisorption capacity than Cu-Cr and Cu/SiO2-I. The selectivity to furfuryl alcohol, at 383 K and 10 bar, using 2-propanol as solvent, was 100% in all of the cases. The pattern for the hydrogenation rate per gram of Cu was: CuMgAl > Cu/SiO2-PD > CuZnAl > Cu-Cr > Cu/SiO2-I. Instead, the hydrogenation rate per Cu atom on the surface (TOF) followed the pattern: CuMgAl > Cu-Cr > Cu/SiO2-PD ≅ CuZnAl > Cu/SiO2-I. These are promising results for the future replacement of polluting Cu-Cr industrial catalysts by a Cr-free one. The highest activity of CuMgAl was attributed to an intimate and effective interaction between Cu0 atoms and Mg2+ cations in a spinel-like matrix. Additional catalytic tests, varying reactant initial concentration and temperature, were performed with CuMgAl catalyst. A negative reaction order (≅ −1) respect to furfural and a high apparent activation energy (≅ 127 KJ mol−1) were estimated, indicating a very strong adsorption of furfural on metal copper surface.

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