Surface characterization of borated y-alumina by using proton affinity distributions

Borated aluminas with different boria contents (2, 3, 5 and 8 wt.% B2O3) were prepared to be used as supports for hydrotreating CoMo catalysts. The borated aluminas were characterized by proton affinity distributions (PAD) to obtain information about changes caused by boron introduction in the surface hydroxyl groups. The later being the sites by means of Mo and Co are anchored to the support. Two new peaks, which cannot be attributed to alumina hydroxyl groups, were found in the PAD profiles of borated aluminas. These two new peaks increased with increasing boria loading, even, in the PAD profile of the alumina with 8 wt.% B2O3 almost no other peaks were present. By comparing PAD profiles with FT-IR spectra of both the OH stretching (3900-3400 cm-1) and the skeletal (under 2000 cm-1) regions, it was possible to assign these new peaks to hydroxyls linked to trigonal and tetrahedral borated species, respectively. Thus, it could be inferred that boria OH groups progressively replaced alumina ones with increasing boria content forming a cover layer. Trigonal borated species were always predominant, however the relative population of tetrahedral species increased with increasing boria content.