Preparation of Ni/SiO2 catalyst with high thermal stability for CO2-reforming of CH4

Silica-supported nickel (Ni/SiO2) catalysts were prepared by homogeneous precipitation of nickel hydroxide in a wet silica gel derived from a sol-gel process (HPG). Their microstructures and their catalytic performance for the CO2-reforming of CH4 were investigated in comparison with those of Ni/SiO2 prepared by a conventional incipient wet impregnation process (IMP). The HPG process consists of two successive steps: gelation of silica in the presence of nickel nitrate and urea at 20degreesC, followed by aging at higher temperature, typically at 80degreesC,to induce thermal decomposition of the urea. The nickel metal surface area of the HPG catalysts was larger than that of IMP catalysts at each calcination temperature. Nickel species in HPG catalysts are expected to be entrapped in the network of silica with high dispersion, while those in IMP catalysts are expected to aggregate on the surface of silica. The characteristic structure in HPG catalysts is considered to be formed through concurrence of dissolution-reprecipitation of silica and entrapment of nickel species into the network. Such processes are promoted in a basic condition led by NH3 formation during thermal decomposition of urea at 80degreesC. The amount of carbon deposited and the catalytic deactivation degree in HPG catalysts were smaller than those in IMP catalysts. Thermal stability of HPG catalysts was much higher than that of IMP catalysts and catalytic activities of the former were higher than those of the latter. This originates in the highly-dispersed nickel metal particles in the rigid network of silica for HPG catalysts. (C) 2002 Elsevier Science B.V. All rights reserved.