Adsorption of Carbon Dioxide in Non-Lo''wenstein Zeolites

We investigated the effect of the aluminum distributionin theadsorption properties of carbon dioxide in the MFI, MOR, and ITW zeolites.Because of its lack of experimental evidence and theoretical validation,Lo''wenstein's rule was not generally imposed, and specialattention was paid to the effect of the Al-O-Al linkages.To this end, we first generalized an existing transferable force fieldfor CO2 adsorption in non-Lo''wenstein zeolites. Bymeans of molecular simulations based on this force field, we showedthat the carbon dioxide adsorption efficiency in MFI is determinedby the number of Al atoms, rather than by their distribution in theframework. This was attributed to the small size of the CO2 molecules compared to the 3D wide-channel topology of the structure.Conversely, we found that the Al distribution has a higher impacton the heat of adsorption in MOR. Although structures with a veryhigh and very low number of non-Lo''wenstein bonds presentedsignificant differences, the bonds themselves do not affect the heatof adsorption directly. Instead, we found that an homogeneous distributionof the Al atoms in the sites forming the C-channel is more favorable.Finally, the small-pore distribution of the ITW zeolite led to highvalues of the heat of adsorption and wide error bars, which made thestudy feasible just for low aluminum concentrations. In that case,we report a small dependency of the heat of adsorption on the Al distribution.

Automated summary

We examined the impact of aluminum distribution on CO2 adsorption properties in MFI, MOR, and ITW zeolites. Through molecular simulations, we found that CO2 adsorption in MFI is determined by the number rather than the distribution of aluminum atoms. In MOR, the distribution of aluminum in the C-channel plays a crucial role in heat adsorption. ITW zeolite, with its small-pore structure, showed high heat adsorption values only at low aluminum concentrations.