Ab initio investigation of the relative stability of silicogermanates and their (Alumino)Silicates counterparts

Abstract

Abstract The diversity of synthetic zeolites with silicogermanate composition has grown significantly. Many of these zeolites have large pores, thanks to the double 4-ring (d4r) structural subunits occupied by Ge atoms. The wide pores make them potentially interesting for catalytic transformation of bulky molecules, but the thermal and hydrothermal stability and the acidity are insufficient for practical applications. In the present work, the stability of known silicogermanate zeolite structures and their silicate and aluminosilicate analogues is evaluated using periodic density functional theory calculations. The thermodynamics of isomorphic substitution of Ge atoms for Si and Al via chemical processes are investigated. The study reveals that thermodynamically, (alumino)silicate counterparts of all known silicogermanates are intrinsically stable, and that the energetics of isomorphic substitution reactions of Ge atoms are almost independent of the distribution of d4r units in the different framework topologies. Chlorides are found better isomorphic substitution reagent candidates, at least theoretically. This work opens perspectives for the catalytic use of stable derivatives of silicogermanate zeolites.