Studies of surface NiO species in NiO/SiO2 catalysts using temperature-programmed reduction and X-ray diffraction

Three different kinds of nickel-containing species have been found in silica-supported nickel oxide samples according to their different reducibilities during temperature-programmed reduction (TPR). Species A is similar to bulk phase nickel oxide, species B is attributed to SiO4 containing nickel oxide particles and species C is a stoichiometric or non-stoichiometric nickel silicate. Examination of the effects of silica-supported NiO particle size on the reducibility shows that the difference in the ease of reduction of NiO crystallites may be caused by the penetration of silica into the lattice of NiO; moreover, the presence of SiO4 groups can retard the sintering of NiO.