Physico-chemical characterisation of impregnated and ion-exchanged silica-supported nickel oxide

Abstract

X-ray analysis, reflectance spectroscopy, analytical electron microscopy and X.p.s. measurements have been used to investigate the influence of the preparation method on the dispersion and interaction of nickel oxide on silica. Two series of solids containing up to 10 wt % NiO were prepared, respectively, by pore volume impregnation and ion-exchange methods. It was found that impregnated samples are poorly dispersed and contain essentially bulk-like NiO crystallites or aggregates. Only in the sample with the lowest nickel content (2 wt % NiO) may the presence of a second nickel species be deduced. Conversely, ion-exchanged samples are well dispersed and give no evidence of the presence of NiO, but rather contain a surface layer of nickel hydrosilicate. The results were used to account for the dramatic difference in the reducibility of impregnated and ion-exchanged samples.