X-ray Photoelectron-spectroscopy Investigation of Pumice-supported Nickel-catalysts

Pumice-supported nickel catalysts, prepared by the method of slow homogeneous 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 analysis indicated large segregation of nickel to the surface. The treatment with H-2 at 673 K and 1073 K produced a partial reduction of Ni+2 to 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 diffraction. A decrease of the Ni 2p/Si 2p intensity ratio occurring in the 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 sintering of the nickel particles and to diffusion of nickel atoms interacting with oxygen vacancies of the support.