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. The K interaction with dicarbonate CO species pushes the cation from 8R site in full analogy with the carbonate's deblocking studied earlier. The easy CO formation in NaMeA is confirmed by modeling reaction of CO formation at the DFT GGA (PBE-D3) and hybrid levels (B3LYP, HISS, HSE06) with cNEB. The calculated intensities for high and low frequency branches of valence vibrations in CO are compared with calculated ones for MeCO molecules and known IR spectroscopic data in the NaMeA zeolites. This new mechanism of deblocking could be important for a wide family of narrow pore zeolites (CHA, RHO, KFI, ) at room temperature where the carbonates are observed in the IR spectra. The possibility of tricarbonate formation is discussed.