A forgotten participant in pore deblocking of zeolites: dicarbonate in NaMeA zeolites, Me = Na, K, Rb, Cs.

The dynamics of carbon dioxide, carbonate anion (CO), and dicarbonate anion (CO) in NaKA zeolite is studied at the DFT GGA level using molecular dynamics (AIMD). We show the easy formation of CO dicarbonate from the reaction between CO and CO at high CO loading and their equilibrium at low CO loading. We have found that the dicarbonate anion can contact up to six cations (Me and Na, Me = Na, K, Rb, Cs), which could reduce the separation properties of NaMeA zeolites relative to CO mixtures.

Carbonate-Promoted Drift of Alkali Cations in Small Pore Zeolites: Ab Initio Molecular Dynamics Study of CO in NaKA Zeolite.

An effect of deblocking of small size (8R, D8R) pores in zeolites due to cation drift is analyzed by using ab initio molecular dynamics (AIMD) at the PBE-D2/PAW level. The effect of carbonate and hydrocarbonate species on the carbon dioxide uptake in NaKA zeolite is demonstrated. It is shown that a hydrocarbonate or carbonate anion can form strong complexes with K cation and withdraw it from the 8R window, so that the probability of CO diffusion through 8R increases.

The role of water in the elastic properties of aluminosilicate zeolites: DFT investigation.

The bulk and Young moduli and heats of hydration have been calculated at the DFT level for fully optimized models of all-siliceous and cationic zeolites with and without water, and then compared to the corresponding experimental data. Upon the addition of water, the monovalent alkali ion and divalent alkaline earth ion exchanged zeolites presented opposite trends in the elastic modulus. The main contribution to the decrease in the elastic modulus of the alkali ion exchanged zeolites appeared to be a shift of cations from the framework oxygen atoms upon water addition, with the coordination number often remaining the same.