Effect of the functional groups of carbon on the surface and catalyticproperties of Ru/C catalysts for hydrogenolysis of glycerol

Abstract

Ruthenium catalysts supported on activated carbons, original (AC) and treated with nitric acid (AC-Ox) were prepared by incipient wetness impregnation from either chloride (Cl) or nitroxyl nitrate (n) precursors. These catalysts were characterized by TG, XPS, TEM, TPD-MS and CO adsorption microcalorimetry and evaluated in the hydrogenolysis of glycerol in the liquid phase, at 453 K and 8 MPa. Studies by TEM show that ruthenium particles supported on AC-Ox are larger than on AC, without any effect of the nature of the metal precursor. However, adsorption of CO on the ex-chloride catalysts is inhibited in comparison with that of the ex-nitroxyl nitrate catalysts. Catalysts characterization by TG, TPD-MS and XPS reveals that the nitric acid treatment and the nitroxyl nitrate precursor generate oxygenated groups on the carbon surface, which provide acid properties to the catalysts, although they are partly destroyed during the reduction treatment applied to the catalysts. The sequence of the overall TOF, Ru(Cl)/AC < Ru(n)/AC < Ru(Cl)/AC-Ox ≈ Ru(n)/AC-Ox, reasonably parallels the population increase of surface acid groups. Participation of the COOH groups in the transformation of glycerol into 1,2-propanediol is verified by using the admixture Ru(Cl)/AC+AC-Ox as catalyst. In this case, since AC-Ox was not thermally treated and no loss of oxygenated groups occurred, TOF and selectivity toward 1,2-propanediol improve in comparison with those of the more active catalysts.