A non-alkoxide sol–gel route to highly active and selective Cu–Cr catalysts for glycerol conversion

Abstract

A non-alkoxide sol–gel route to highly active and selective Cu–Cr catalysts for glycerol conversion is presented. The addition of propylene oxide to ethanol solutions of Cr(NO3)3·9H2O and Cu(NO3)2·3H2O resulted in the formation of transparent Cu–Cr gels. The resulting gels were converted to the Cu–Cr catalysts by atmospheric drying and calcination. The Cu–Cr catalysts are characterized by X-ray diffraction (XRD), N2 physisorption, temperature-programmed reduction (TPR), and transmission electron microscopy (TEM). The results show that the surface area of the Cu–Cr catalyst is adjusted by the hydrolysis conditions, Cu/Cr molar ratio, and treatment conditions (such as gas atmosphere and final temperature). For the sample with Cu/Cr = 0.5, the surface area of Cu–Cr xerogel can reach 94 m2/g and decreased to only 31 m2/g after calcination at 500 °C. The catalysts show significant catalytic activity and selectivity in glycerol conversion, i.e. above 52% conversion of glycerol and above 88% selectivity to 1,2-propanediol at 210 °C and 4.15 MPa H2 pressure. CuCr2O4 supported Cu catalysts are much more active than Cr2O3 supported Cu catalysts. This indicates a strong interaction between Cu and CuCr2O4 that is significantly improving the effectiveness of the catalyst for glycerol conversion.