LITTLE ENERGETIC LIMITATION TO MICROPOROUS AND MESOPOROUS MATERIALS

A series of pure-silica or high-silica zeolites, several mesoporous si licas, moganite, and the conventional silica polymorphs (tridymite, cr istobalite, coesite, glass) are energetically, at most, 15 kJ/mol high er than quartz, with the energy versus volume curve leveling off about 15 kJ per mol of SiO2 above quartz for large volumes. For AlPO4 polym orphs, a similar trend holds, with energy leading off at an even less metastable value, namely about 10 kJ per mol of Al0.5P0.5O2 above berl inite. These small energy differences are consistent with self assembl y of these materials being geometrically and kinetically, rather than energetically, controlled. Thus there is very little energetic limitat ion to the possibility of synthesizing various micro- and mesoporous f ramework structures.