A Simulated Annealing Study of Si,Al Distribution in the Faujasite Framework

Sevetai important properties of faujasite are concerned with the Si, Al distribution in its framework.In the Present study,a starting configuration of the disttibution is generated with randomly positioned Si, Al. After the simulated annealing procedure, some orderings appear in the optimized configurations of the system and lead to a series of consequences,some of which have aleady been obtained by pioneer studies concerning ordering schemes.In optimized configurations,a certain degree of disorder reasonably is maintained because of the use of standard Monte Carlo finite temperature techniques, which brings about a realistic employ of the numerical simulation. The calcutated Al distribution on the first shell of the Si site is assessed by ²⁹ Si MAS NMR experiments;the calculable Al distribution on the second shell of the Al site is related with the acidity of faujasite; the electrostatic energy calculation provides possible explanation on the observed discontinuity in the plot of unit-cell parameter against Al content.