X-RAY PHOTOELECTRON-SPECTROSCOPY INVESTIGATION OF PUMICE-SUPPORTED NICKEL-CATALYSTS

Pumice-supported nickel catalysts, prepared by the method of slow homo geneous precipitation with urea, were analysed by x-ray photoelectron spectroscopy (XPS). By comparison with similarly prepared silica- and alumina-supported nickel catalysts, a preferential interaction of Ni2 with Al3+ of the support has been determined. A quantitative XPS anal ysis indicated large segregation of nickel to the surface. The treatme nt with H-2 at 673 K and 1073 K produced a partial reduction of Ni+2 t o Ni-0. The extent of the reduction was largest at 1073 K and in this case the reduced Ni in the metallic phase was detectable by x-ray diff raction. A decrease of the Ni 2p/Si 2p intensity ratio occurring in th e lower temperature H-2-treated catalysts was attributed to diffusion of nickel as Ni2+, as a consequence of a solid-state reaction between nickel ions and support oxides, whereas the decrease of the intensity ratio in the high-temperature reduced catalysts was attributed to sint ering of the nickel particles and to diffusion of nickel atoms interac ting with oxygen vacancies of the support.