The Synthesis Of High Surface Area Cu-Cr Catalysts And Catalytic Properties For Glycerol Hydrogenolysis

Cu-Cr catalysts are of particular interest due to their interesting catalytic properties. Recently, it has been demonstrated that Cu-Cr catalysts are the most effective for glycerol hydrogenolysis at low pressure. Therefore, a high surface area and highly porous Cu-Cr catalyst could significantly impact many areas of catalysis, especially for the glycerol hydrogenolysis. High surface area, highly active and selective Cu-Cr catalysts have been prepared via a facile carbon templating route and a non-alkoxide sol-gel route. The obtained catalysts were characterized by N₂ physisorption, temperature-programmed reduction (TPR), X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The catalytic properties of the nanostructured Cu-Cr catalysts were evaluated by glycerol hydrogenolysis. The results show that:1. High surface area Cu-Cr catalysts with different Cu/Cr molar ratios have been synthesized by using carbon materials as templates and copper and/or chromium nitrates as precursors. The specific surface area of the obtained Cu-Cr catalyst can reach above 50 m²/g, while those of CuO and Cr₂O₃ are about 10 and 50 m²/g, respectively. The surface area of Cu-Cr catalyst can be controlled by carbon templates, Cu/Cr molar ratios, and the treatment atmosphere and final temperature. The reduced Cu-Cr catalysts show significant catalytic activity and selectivity in glycerol hydrogenolysis, i.e. above 51 % conversion of glycerol and above 96 % selectivity to 1,2-propanediol at 210℃and 4.15 MPa H₂ pressure. The Cu-Cr catalysts with Cu/Cr molar ratio lower than 1:1 present higher conversion of glycerol, however the commercial copper-chromite catalysts with Cu/Cr molar ratio of 1:1 show high activity. Templating route is of great potential in the controlled synthesis of Cu-Cr catalysts with high surface area as a highly active and selective catalyst for glycerol hydrogenolysis. The templating route can be easily extended to prepare other catalysts, such as high surface area nanoscale Ce_xFe_1-xO₂ solid solutions.2. Highly active and selective Cu-Cr catalysts with different Cu/Cr molar ratios have been synthesized by a non-alkoxide sol-gel route and copper and/or chromium nitrates as precursors, and epoxides for gelation. The surface areas of Cu-Cr catalysts can be controlled by the hydrolysis conditions, Cu/Cr molar ratios, and treatment conditions (i.e., gas atmosphere and final temperature). The catalysts show significant catalytic activity and selectivity in glycerol hydrogenolysis, i.e. above 52 % conversion of glycerol and above 88.2 ï¼…selectivity to 1,2-propanediol at 210℃and 4.15 MPa H₂ pressure. In addition,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 hydrogenolysis. This non-alkoxide sol-gel route could be easily extended to the preparation of many other catalysts from simple metal ion salts instead of metal alkoxide precursors.