An attempt to predict and rationalize relative stabilities and preferential germanium location in Si/Ge zeolites

The preferential substitution of Ge in AST, ASV, BEA, BEC, ISV and LTA has been calculated within an atomistic force field methodology and the use of a Si/Ge potential for zeolites. The results show a linear correlation between SiOGe angle and the resultant energy, this meaning that tetrahedral position yielding low SiOGe angles are energetically favoured. In general, tetrahedral (T) positions in double four rings (D4R) show low angles and this explains the preferential location of Ge in D4R. Computational chemistry is used in this work to estimate the energies of formation for BEA, BEC and ISV zeolites and the variation of the relative stability of these structures with respect to Ge content which are in good agreement with experimental heats of formation.