ИСТИНА

Interplay of an available space for reaction center and mobility of alkali cations leads to crucial role of cell parameters for accurate calculation of activation barrier of CO2 hydration in optimized MeX zeolite cells (Me = K, Rb, Cs) after Me cation exchange. While the CO2 hydration is modeled in the MeX forms (Me = K, Rb, or Cs) with a fixed volume of NaX one, barrierless reaction is predicted for Me = Rb or Cs that is not confirmed by experimental data. If cell parameters are optimized with VASP according to the new Me cations after Na/Me exchange, Me = Rb or Cs, small activation energy is obtained in agreement with room temperature conditions of the CO2 hydration. Earlier [1], heats of CO2 hydration in optimized MeY zeolite cells showed thermodynamic allowance of hydration for K and Cs (small positive heats for K or small negative heats for Cs compared to high positive heats for Li and Na) in agreement with IR data [2]. All the data for MeX and MeY zeolites are discussed together regarding 3- or 2-cation reaction centers in MeX and 3- or 4-cation sites with obtained hydrocarbonate in MeY, Me = K, Cs.