Effect of phosphorus on the activity of Cu/SiO2 catalysts in the hydrogenolysis of glycerol

Abstract

The modification effect of P2O5 on Cu/SiO2 catalysts was studied for the hydrogenolysis of glycerol. A series of Cu/P(y)-SiO2 catalysts with three different loadings of P2O5 (2, 3 and 4 wt%) was prepared by successive wet impregnation, and characterized using X-ray Diffraction (XRD), nitrogen sorption, surface acidity technique, UV-Diffuse Reflectance Spectroscopy (UV-DRS) and X-ray Photoelectron Spectroscopy (XPS). The catalysts were evaluated in a batch reactor at 220 °C and 5 MPa of H2. The addition of phosphorus increased the activity, with the highest activity being achieved over the Cu(x)/P(y)-SiO2 catalyst with P2O5 loading of 2 wt%. The increased activity was attributed to a combination of geometrical and electronic effect induced by P2O5 on Cu metallic species. In fact, UV-DRS and TPR measurements showed the existence of a Cu-P interaction, which can increase the distance of the Cu-Cu metal bond, and consequently increase the electron density; this effect enhanced the catalytic activity, compensating for the decrease of Cu dispersion (derived from XPS results). However, this applies only to catalysts with low P2O5 loadings because the loss of actives sites by the formation of aggregates at higher P2O5 loading cannot be compensated for by Cu-P interaction. The addition of P2O5 changes the products distribution because the high electron density of Cu-P favors the adsorption of the Csingle bondO bond on glycerol.