Influence of carbonate species on elastic properties of NaX and NaKX zeolites

Carbonates in zeolites: Formation, properties, reactivity

“…The charges of O z atoms are larger than those of O c atoms in 1.3 times. The slight variation of Bader atomic charges on addition of carbonates is a convenient feature facilitating an application of MC or MD approaches to the carbonates in zeolites . These estimates are important for adsorption modeling when authors try to consider a new set of the charges to take into account the presence of carbonates.…”

“…The stabilization of deserves a short comment. The intuitive explanation of easier formation of with higher exothermic effect compared with is the smaller charge of (−0.868 against −1.690 e in Table ). The higher charge should be related to the large quantity (four) of NaIII cations shifted by an essential vector of 1.404 Å and more (Table ) to optimize chemisorbed .…”

“…[2,3] The authors [2] noted that excluded volume for CO 2 adsorption in CsY corresponds to five molecules per unit cell at CO 2 pressure of 14 bar and temperature of 303 K. Respective detailed experimental evaluations were analyzed by Calero's group for H 2 adsorption in NaX (FAU zeotype), NaA, NaCaA (LTA zeotype). [3] However, all the results of this work related to modeling of adsorption have been performed without addressing to microscopic picture of carbonates discussed using density functional theory (DFT) [4][5][6][7] or molecular mechanic [8] approaches. Microscopic models of carbonate species were optimized and discussed for the NaKA, [4,5] NaX, [7,8] MeRHO, [6] MeMOR [5] zeolites, Me 5 Li, Na, K, Cs, Mg, Ca, Ba, and a wide set of cluster models with diversified geometries (8R, 6R14R, 10T) and similar cations.…”

“…[3] However, all the results of this work related to modeling of adsorption have been performed without addressing to microscopic picture of carbonates discussed using density functional theory (DFT) [4][5][6][7] or molecular mechanic [8] approaches. Microscopic models of carbonate species were optimized and discussed for the NaKA, [4,5] NaX, [7,8] MeRHO, [6] MeMOR [5] zeolites, Me 5 Li, Na, K, Cs, Mg, Ca, Ba, and a wide set of cluster models with diversified geometries (8R, 6R14R, 10T) and similar cations. [5] More precisely, one has considered the thermodynamic aspect of formation of carbonates and hydrogen carbonates in MeRHO forms regarding various alkaly forms and Si/Al ratio.…”

Deblocking effect of carbonates and hydrogen carbonates in the alkali form zeolites with narrow pores

“…Such effect can lead to a destabilization of the system even at low Si/Al ratio, when the number of the cations is large enough. Respective example, resulting in the decrease of Young moduli upon CO 3 À2 formation in the NaX zeolite, has been recently demonstrated using various force fields and the GULP code [30]. In this respect the compensating role of alkali cations has to be very important for the stability of the carbonates.…”