Surface properties of alumna modified with barium and strontium cations

The EPR method in conjunction with the 2,2,6,6-tetramethylpiperidine-1-oxyl and anthraquinone molecular probes and IR spectroscopy of adsorbed carbon oxide (CO) were used to study the electron-acceptor properties of gamma -Al 2O3 modified with strontium and barium cations. It was found that such a mo dification results in the formation of an X-ray-amorphous surface layer com posed of the corresponding aluminates and characterized by its own Lewis ac idity. It was demonstrated that the concentration and strength of Lewis aci dic sites (LASs) (coordination-unsaturated aluminum ions) at the alumna sur face decreased upon its modification. At the same time, local LASs concentr ations remained high, as at the initial alumna surface. It was established that the electron-donor properties of the gamma -Al2O3 surface modified wit h strontium and barium cations are much weaker in comparison with gamma -Al 2O3 modified by calcium cations.