The influence of spatial limits on the modeling chemical reactivity: The example of CO2 hydration in MeX zeolites (Me = K, Rb, Cs)

摘要

Zeolite cell size variations upon cationic exchange are frequently disregarded while calculating chemical reactions with rather bulky reagents. An example of the reaction between the small reagents (H2O and CO2) illustrates a necessity to check this assumption for faujasite (FAU) zeolites with large porous space. The interplay of the space for the reaction center and the mobility of alkali cations forces lattice parameters to play a crucial role for the accurate computation of activation barrier of CO2 hydration. While the CO2 hydration is modeled in the MeX forms (Me=Rb, or Cs) with a fixed volume of NaX one, barrierless reactions were predicted that is not confirmed by experimental data. When the RbX and CsX cell parameters were optimized with Vienna Ab-initio Simulation Package (VASP), activation energies were obtained in agreement with the experimental data that CO2 hydration in CsX occurs at room temperature.