Theoretical approach to the basicity of alkaline-earth-metal oxide catalysts. Relationship between basicity and surface structure of magnesium oxide

Abstract

Molecular-orbital calculations of cluster models for various structures of the MgO surface have been performed in order to clarify the relationship between basicity and microscopic structure. The surface is regarded as being constructed of many long —MgO— chains interwoven or entangled in a complex manner. Ways in which interactions between the chains affect the basicity of an oxygen site are discussed. The main factors generating stronger basicity are concluded to be (i) fewer Mg atoms coordinated to the central oxygen atom in the basic site and (ii) more O atoms coordinated to the Mg atoms adjacent to the central oxygen atom. This result agrees well with the experimental fact that magnesium hydroxide is dehydrated to a basic catalyst with the maximum number of basic sites by calcination at an appropriately moderate temperature.