Role of cerium as a promoter and process optimization studies for dehydration of glycerol to acetol over copper chromite catalyst

Abstract

Cerium-promoted silica supported copper chromite catalyst was synthesized from acid hydrolysis of sodium silicate by sol–gel method. The catalyst was characterized by Brunauer–Emmett–Teller (BET) method, field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), NH3-temperature programmed desorption (NH3-TPD) and pyridine adsorbed Fourier transform infrared spectroscopy (Py-FTIR). Among cerium doped catalysts, 5 wt% of Ce promoted copper chromite supported by 40 wt% of silica (SiCuCr40–Ce5) shows the largest BET surface area. XRD analysis of the reduced form of the catalyst shows both CeO2/Ce2O3 redox system and CuO/Cu2O/Cu redox system. Py-FTIR shows the maximum number of Lewis acid sites for SiCuCr40–Ce5 than others. The highest acetol selectivity with analytical reagent (AR) grade glycerol conversion is observed for SiCuCr40–Ce5 at 200 °C for 3 h in a batch reactor at atmospheric pressure. Cerium promotion lowers the reaction temperature with enhanced glycerol conversion and increased acetol selectivity. Though the above catalyst shows higher conversion for laboratory reagent (LR) grade glycerol but it reduces acetol selectivity. The addition of glucose into the LR grade glycerol further reduces glycerol conversion and decreases the acetol selectivity to zero. This may be due to the presence of iron as impurity in LR grade glycerol. XRD analysis of spent catalyst shows the absence of redox catalytic system and the pore volume reduces identified by BET analysis. Raman analysis of the spent catalyst shows graphite-like carbon deposition in the spent catalyst.