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

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)center dot 9H(2)O and Cu(NO3)(2)center dot 3H(2)O 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), N-2 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 m(2)/g and decreased to only 31 m(2)/g after calcination at 500 degrees 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 degrees C and 4.15 MPa H-2 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.