Synthesis and thermal stability of Ni, Cu, Co, and Mo catalysts based on high surface area silicon carbide

Abstract

The potential of high surface area silicon carbide as catalyst support has been evaluated regarding the metal–support interaction (MSI), metal–support stability (MSS), and affinity for ion-adsorption. Nickel, cobalt, copper, and molybdenum catalysts have been prepared by incipient wetness impregnation. These SiC based catalysts all show after calcination at 773 K, an MSI lower than that of their silica and alumina based counterparts. Reaction of the metal with SiC at elevated temperatures may cause the formation of metal silicides and limits the maximum temperature of application. The MSS of the incipient wetness Ni/SiC catalyst is high. An easily reducible NiO species is retained on the SiC surface after calcination at 1273 K, whereas substantial deactivation of the Ni/Al 2O 3 and Ni/SiO 2 catalysts occurs. These results suggest a high potential of Ni/SiC catalysts in high-temperature processes. Highly dispersed Ni/SiC catalysts (the diameter of the nickel particles equals 4 nm) have been prepared by adsorption of Ni(NH 3) 4(H 2O) 2 2+ on SiC. The nickel is thus grafted on SiC and SiO 2 as nickel silicate (antigorite). The formed amount of antigorite per unit surface area is on SiC three times higher than that on silica, which points to the presence of a very reactive oxidic layer on the SiC. Calcination at 1273 K causes substantial SiC conversion and nickel sintering, which points to a low MSS, in contrast to the Ni/SiC catalyst prepared by incipient wetness. This probably originates from the intimate contact of the nickel phase with the SiC surface and the resulting catalyzed oxidation of the SiC.