Molecular Dynamics Simulation of the Cation Motion upon Adsorption of CO₂ in Faujasite Zeolite Systems

Abstract

Molecular Dynamics simulations have been carried out in NaX and NaY Faujasite systems to deepen understanding of the cation rearrangement during the CO2 adsorption process suggested by our recent diffusivity measurements. This study is a major contribution since the rearrangement of the cations in Faujasite, the most promising adsorbent for CO2 storage, can represent a significant breakthrough in understanding the adsorption and diffusion processes at the mircroscopic scale. For NaY, it has been shown that at low and intermediate loadings, SII cations can migrate toward the center of the supercage due to strong interactions with the adsorbates, followed by a hopping of SI'cation from the sodalite cage into the supercage to fill the vacant SII site. The SI cations are only displaced at a higher loading, leading to cation de-trapping out of the double six rings into the vacant SI' sites. For NaX, the SIII' cations which occupy the most accessible adsorption sites move significantly upon coordination to the carbon dioxide molecules. The SI' and SII cations remain consistently located in their initial sites whatever the loading. Indeed, the most probable migration mechanism involves SIII' cation displacements into nearby vacant SIII' sites.

CO2 diffusivity in LiY and NaY faujasite systems: a combination of molecular dynamics simulations and quasi-elastic neutron scattering experiments

“…This is supported by our recent GCMC simulations (Maurin et al accepted) which revealed for LiY a higher enthalpy of CO 2 adsorption at low coverage due to an average Li + (SII)-O(CO 2 ) distance (2.10 Å) shorter than the Na + (SII) analogue (2.50 Å). However, our MD simulations show that beyond the initialisation of the diffusion, there is also a concerted (Li + -CO 2 ) motion similar to those previously pointed for Na + (Plant et al 2006) which induces a redistribution of the cations within the supercage. An illustration of the rearrangement of Li + upon CO 2 diffusion is provided in Fig.…”

Insights on the Anomalous Adsorption of Carbon Dioxide in LTA Zeolites

“…Besides other experimental conditions (such as pressure, temperature, and moisture), the topology, and composition of the zeolite govern the forces involved in the adsorption process and the overall adsorption efficiency. For instance, at low pressure the amount of CO 2 adsorbed appears to be highly influenced by the nature and density of the cations inside the zeolite pores, [4][5] whereas the pore shape and volume appear to control the adsorption capacity at high pressures. 6 Molecular simulation is a powerful tool to accurately predict adsorption and diffusion processes in crystalline porous materials, 7 and has been extensively used for predicting the adsorption of carbon dioxide in zeolites.…”

Adsorption of CO2 and N2 on synthesized NaY zeolite at high temperatures

“…Regarding CO 2 adsorption and separation, it is of great significance to obtain high CO 2 adsorption capacity because the CO 2 adsorption behavior greatly influences the CO 2 separation and desorption processes on NaY particle and membrane. A number of efforts have been made to address CO 2 adsorption behavior via different adsorbents and techniques (Lee et al 2002;Harlick and Tezel 2004;Li and Tezel 2007;Siriwardane et al 2003;Jaramillo and Chandross 2004;Khelifa et al 2004;Li et al 2000Li et al , 2008Walton et al 2006;Maurin et al 2005;Gao et al 2004;Kusakabe et al 1997, Plant et al 2006Sebastian et al 2007;Chou and Chen 2004;Othman et al 2006;Zheng and Gu 1998). Yong et al (2002) reviewed the adsorption of CO 2 on different adsorbents at relatively high temperatures.…”