A SIMULATED ANNEALING STUDY OF CATION DISTRIBUTION IN DEHYDRATED NA-EXCHANGED FAUJASITE ZEOLITES

A simulated annealing method is employed to study the cation distribut ion in dehydrated Na-exchanged faujasite zeolites. By use of the same three parameters, i.e. e(I)-e(I), e(II)-e(I), the site energy level di fferences between the cations on the different cation sites I, I' and II, and w, the repulsive energy between cation pairs located on adjace nt sites I and I', the cation distribution in dehydrated NaHY-type zeo lites (with a Si/Al ratio of 2.46) with varying cation loading or temp eratures could be accurately predicted. These parameters were determin ed by fitting the simulated results with experimental data report in t he literature. It is found that the influence of the framework Al cont ent, <(N-Al)over bar>, on the site energy level differences can be exp ressed as e(I')-e(I) = -23.0490 + 0.5605<(N-Al)over bar> KJ mol(-1) an d e(II)-e(I) = 22.4770 + 0.4437<(N-Al)over bar> KJ mol(-1). By use of these linear relations and a refined w = 40 KJ mol(-1), the cation dis tribution of dehydrated Na-exchanged faujasite with various Al content could be predicted excellently. (C) 1997 Elsevier Science Ltd.