Preparation and characterization of nanocrystalline CuAl2O4 spinel catalysts by sol–gel method for the hydrogenolysis of glycerol

Samples of nanocrystalline copper aluminate (CuAl2O4) were prepared using various calcination temperatures and surfactant concentrations of citric acid via a sol–gel method for the hydrogenolysis of glycerol. A variety of techniques, including TPR, H2-TPD, XRD and XPS, were used to characterize the samples. Crystallized CuAl2O4 was initially observed after calcination at the temperature of 600 °C and only peaks corresponding to CuAl2O4 spinel crystal were observed at 800 °C. The citric acid concentration influenced the size of the CuAl2O4 crystal (ca. 10–30 nm) and the electron state of Cu after reduction, which optimized the ratio of metal precursor cations and citric acid with 1 to 2. Catalytic activities of the prepared catalysts were examined for the hydrogenolysis of glycerol to 1,2-PDO. CuAl2O4 catalyst calcined at 800 °C, which contains only the CuAl2O4 crystalline phase, showed the highest catalytic performance with over a 90% conversion and selectivity. This can be attributed to the exceptional reducibility of Cu species and hydrogen adsorption/desorption ability among the catalysts studied.

Graphical abstractThe nanocrystalline copper aluminate (CuAl2O4) was synthesized via the sol–gel method assisted by citric acid with particle sizes of 10–30 nm. Prepared CuAl2O4, which was treated at 800 °C, showed high performance (conversion and selectivity of over 90%) in hydrogenolysis of glycerol to 1,2-PDO. The catalyst formed well the spinel structure, and it showed the highest reducibility and hydrogen adsorption and desorption ability with amount of occluded hydrogen, which are major determinants of catalytic activity in this reaction.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Nanocrystalline CuAl2O4 spinel catalysts were prepared by sol–gel method. ► Catalysts for hydrogenolysis of glycerol to 1,2-PDO ► Increasing reducibility of copper at the surface of CuAl2O4. ► Increasing occluded hydrogen in spinel structure of CuAl2O4.