Thermochemistry of microporous and mesoporous materials

The paper reviews thermochemistry contribution to the stability of frameworks and synthetic progress in microporous and mesoporous materials. Knowledge of enthalpies, entropies and free energies of formation on the framework structure in micorporous and mesoporous materials is systematically summarized via several calorimetric measurements. It is found that a series of pure-silica, mesoporous silicas and AlPO₄ polymorphe are energetically, at most, 15 kJ · mol^-1 higher than quartz and berlinite, and the entropies of a series of pure silica zeolites span a very narrow range at 3.2-4.2 J · K^-1 · mol^-1 above quartz. Therefore, the Gibbs free energy of transformation calculated for several SiO2 phases have nearly the same ΔG_tran²⁹⁸ as the values range from 0 to 12.6 J · K^-1 · mol ^-1 with respect to quartz. Thus, there is very little energetic limitation to the possibility of synthesizing various micro- and mesoporous framework structures. In addition, a new calorimetric method, in situ calorimetry, is introduced to reveal the kinetics and nucleation/crystallization in the process of the zeolite synthesis.