Quantum-chemical studies of alumina. Part 1.—Brønsted acidity and basicity

Abstract

This work is part of a series intended to clarify the relationship between the microscopic surface structure and the acid-base nature of the Al₂O₃ system using ab initio molecular-orbital calculations for many cluster models. This paper deals with Brønsted acidity and basicity. The strong acidity of an OH group is caused by the high coordination of Al atoms (maximum 3) to the O atom in the OH group and the low coordination of O atoms to these Al atoms, while strong basicity is obtained by the opposite conditions to the number of atoms around the central O atom of the active site. Terminal OH groups or lattice O atoms in the dehydrated surface of alumina usually have no strong acidity or basicity, respectively, while O atoms in some terminal OH groups have fairly strong basicity.