The enthalpies of formation of a series of high-silica zeolites are only 8–14 kJ/mol less exothermic than that of quartz, with a very weak dependence on volume (framework density), despite a factor of two variation in those parameters. Several mesoporous silicas, with pore diameters in the range 3–5 nm, also are only 14 kJ/mol less stable energetically than quartz. Thus, in the microporous and mesoporous regime, the energy appears to level off at values only about 14 kJ/mol less stable than quartz, with the pores behaving energetically like an inert second phase. Similar trends are seen for AlPO4 zeolites, and for a dehydrated CaAl silicate zeolite. These data suggest that the synthesis of microporous materials is not limited by their energetics but by finding appropriate kinetic pathways for their formation.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Materials Chemistry