Aluminum, trigonal cluster models

Fig. 16. Cluster models of trigonal aluminum LASs in aluminosilicates.

Fig. 18. Cluster models of the molecular adsorption forms of (a) FLO, (b) NH3, and (c) CH3OH on trigonal aluminum.

Fig. 20. Cluster models of two structural types of trigonal aluminum LASs in aluminosilicates. State 1 in structure (b) corresponds to the structural coordination, whereas state 2 represents the adsorption coordination.

The quantum-chemical cluster models of acid base sites of binary oxides have recently been reviewed by Zhidomirov and Kazansky.Concerning the Brensted acid sites of the binary oxide silica-alumina, they summarize as follows. The acid sites acting in typical acid-catalyzed reactions are bridged hydroxyl groups and water molecules coordinated on a trigonal aluminum atom. These centers are characterized by approximately equail surface densities and atomic catalytic activities. 

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