Effect of Phosphorus on Structure and Performance of Cu/Al2O3 Catalysts for Hydrogenolysis of Glycerol

Phosphorus (P) modified Cu/Al2O3 catalyst was prepared by the successive impregnation method. The physicochemical properties of the catalyst were studied by means of N-2 adsorption-desorption, X-ray diffraction, infrared spectroscopy, UV-visible diffuse reflectance spectroscopy, H-2 temperature-programmed reduction, NH3 temperature-programmed desorption, and dissociative N2O adsorption. The effects of the P content and the impregnation sequence on the structure and the performance of the catalyst for the hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO) were discussed. The addition of P to Cu/Al2O3 enhanced the acidity and Cu dispersion, especially when P species was impregnated prior to Cu. Also, there was a strong interaction between P and Cu species. However, the strong interaction leads to the coverage of Cu atoms with the P species at high P content. The coverage may be more serious when the P species was added after Cu to the catalyst. In the hydrogenolysis of glycerol, the addition of P prior to Cu remarkably promoted the catalytic performance of Cu/Al2O3. Under the conditions of 220 degrees C, 3.0 MPa, space velocity of 2.0 h(-1), and the H-2/glycerol molar ratio of 20, as the P content increased from 0 to 6%, the glycerol conversion and the 1,2-PDO selectivity increased from 17.1% to 95.0% and from 83.7% to 97.2%, respectively. The promotion effect of P on the performance of Cu/Al2O3 is attributed to the increase of catalyst acidity as well as the strong interaction between Cu and P species.