Properties Of Carbon Support Research Articles

Influence of oxidation on heat-treated activated carbon support properties and metallic dispersion of Ru/C catalyst

Heat-treated activated carbon has been oxidized to improve the properties related to the use as a support for the preparation of 5wt% Ru/C catalysts by impregnation. The pore structure, surface oxygen groups of the heat-treated activated carbon before and after oxidation in the gas and liquid phase, as well as catalytic activities and dispersion of Ru in the catalysts were investigated systematically. The pore structures of the samples were characterized by N2 physisorption. Temperature-programmed desorption (TPD) was conducted to determine the chemical properties of the samples. Ru dispersion was measured by CO pulse chemisorption. The effects of oxidation treatments on carbon surface chemistry and pore structure which are closely related to Ru dispersion and catalytic activity, was examined. Furthermore, the modified heat-treated activated carbon support obtained by gas phase oxidation in CO2 and liquid phase oxidation in nitric acid was more suitable to prepare Ru-based catalysts for ammonia synthesis than that without treatment.

Study on the formation of Pt/C catalysts by non-oxidized active carbon support and a sulfur-based reducing agent

The formation mechanism of Pt/C catalysts using non-oxidized active carbon support and the weak reducing agent Na2S2O4 was investigated. Platinum on carbon catalysts were fabricated by an impregnation/reduction process of the Pt-precursor H2PtCl6 on carbon support. The effect of thermal treatment in argon up to 700°C on the structural characteristics of these catalysts was studied by XRD and TEM analyses. The importance of carbon support properties on Pt/C formation was recognized. Before thermal treatment a very weak internal organization (a very small particle size and amorphous structure) in the metal was obtained. Thermal treatment at relatively low temperatures leads to the growth and then to the crystallization of platinum particles in the well-known face centered cubic structure. The sintering of Pt particles occurs through the migration of Pt atoms on the carbon support, likely by a bridge-bonding mechanism on sulfur atoms. A fast growth of Pt particles occurred in the temperature range 300—400°C. Thermal crystallization, instead, occurred mostly going from 400 to 550°C. Following annealing at 550°C, the formation of platinum sulfide was revealed. The sample thermally treated at 700°C showed an anomalous XRD pattern with Pt reflexions shifted towards high angles and an increase of Pt[111]/Pt[220] peak intensity ratio.

Effect of carbon support properties on enantioselective hydrogenation of isophorone over palladium catalysts modified with (−)-dihydroapovincaminic acid ethyl ester

The support-effect was investigated in the enantioselective hydrogenation of isophorone over Pd catalysts prepared on different carbon supports. Carbon supports with different specific surface area and activated carbons with different surface chemistry were used. The Pd catalysts, obtained by different reduction methods of the catalyst precursor, had different dispersion. The low dispersion was advantageous for the high enantioselectivity and the different supports had influence on the ee due to their different specific surface area and surface chemistry.