Bonding in Microporous Solids Substitutional Behaviour

These insights into the nature of the chemical bonding also help us understand patterns of framework substitution. In particular, strongly ionic metals readily replace aluminium in phosphates, but less readily in silicates. Once substitution has occurred, QM-based methods can be applied to understand the Lewis acid behaviour of such dopants as they coordinate to adsorbed molecules. The activation of hydrogen peroxide by tetrahedral Ti is of particular importance for selective oxidation and is discussed further in Chapters 7 and 9. 

3 Organic and Inorganic Cation Sites Monte Carlo/ Simulated Annealing Approaches 

The predicted location of extra-framework cation sites in zeolites can also be studied by MC methods, although the problem is further complicated by the disorder in both framework aluminium location (and associated charge) and partial occupancy of cation sites. In this case a large number of possible extraframework cation site distributions has to be considered, and a model assumed for the location of framework charge. 

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