AFI zeolite crystals

The introduction of a T heteroelement may also play a structure-directing effect, changing the phase selectivity of the crystallization, as was previously reported in hydroxide media [108, 109]. In some cases, this selectivity change is simply related to the fact that the isomorphous substitution is very difficult, as is the case for the pure silica SSZ-24 (AFI) or SSZ-31 ( STO) zeolites. In other cases the isomorphous substitution is easier and... 

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