Quantum chemical studies of alumina. Part 3.—Acidity and basicity of the spinel-type crystal

Abstract

The strength of the acidity and basicity of γ- and η-alumina has been investigated with respect to the local structure around the central atoms of the acid or base site (the residual OH group, the exposed O atom or the Al atom) by ab initio molecular orbital calculations for cluster models having geometrical parameters corresponding to the spinel type. The Brønsted acidity and the basicity is significantly affected by the coordinative environment around the site in a topological sense, similarly to Part 1 of this series, where simplified cluster models were used. On the other hand, the following three factors, which may affect the strength of Lewis acidity, have been examined in more detail than that in Part 2: (1) the coordinative environment around the surface Al atom, (2) number of acid Al atoms comprising the acid site and (3) the geometrical structure of the site. The results reveal that some modifications are neccessary to the previous conclusion, although the essential nature is not changed.