The surface reactivity of different aluminas as revealed by their XPS Cls spectra

Aluminium oxides were prepared from different starting materials and by different methods. All aluminas were calcined at 873 K and an alumina gel precursor was heated to various temperatures in the range 373-1273 K. Analysis of the XPS C1s spectra, derived from adsorbed atmospheric hydrocarbons, indicated the presence of varying proportions of different carbonaceous species. A systematic variation was observed for the heat treated gel precursor. XRD results, for the aluminas calcined at 873 K. could not be correlated with the observed differences. The results are interpreted as being due to changes in the properties of active surface sites which depend on sample history and thermal treatment. The XPS C1s spectra also showed that the predominant hydrocarbon reaction was dehydrogenation and that this could be used to characterise the activity of the aluminas. It is proposed that analysis of C1s spectra may be extended to provide a useful method for characterising the surface properties of other oxidic materials.