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

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 impregnati on These SiC based catalysts all show after calcination at 773 K, an MSI lo wer than that of their silica and alumina based counterparts. Reaction of t he metal with SiC at elevated temperatures may cause the formation of metal silicides and limits the maximum temperature of application. The MSS of th e incipient wetness Ni/SiC catalyst is high. An easily reducible NiO specie s is retained on the SiC surface after calcination at 1273 K, whereas subst antial deactivation of the Ni/Al2O3 and Ni/SiO2 catalysts occurs. These res ults suggest a high potential of Ni/SiC catalysts in high-temperature proce sses. Highly dispersed Ni/SiC catalysts (the diameter of the nickel particl es equals 4 nm) have been prepared by adsorption of Ni(NH3)(4)(H2O)(2)(2+) on SiC. The nickel is thus grafted on SiC and SiO2 as nickel silicate (anti gorite). The formed amount of antigorite per unit surface area is on SiC th ree times higher than that on silica, which points to the presence of a ver y reactive oxidic layer on the SiC. Calcination at 1273 K causes substantia l SiC conversion and nickel sintering, which points to a low MSS, in contra st to the Ni/SiC catalyst prepared by incipient wetness. This probably orig inates from the intimate contact of the nickel phase with the SIC surface a nd the resulting catalyzed oxidation of the SiC. (C) 1999 Elsevier Science B.V. All rights reserved.