posted on 2023-06-27, 14:35authored byPablo Romero-Marimon, Juan José Gutiérrez-Sevillano, Sofia Calero
We investigated the effect of the aluminum distribution
in the
adsorption properties of carbon dioxide in the MFI, MOR, and ITW zeolites.
Because of its lack of experimental evidence and theoretical validation,
Löwenstein’s rule was not generally imposed, and special
attention was paid to the effect of the Al–O–Al linkages.
To this end, we first generalized an existing transferable force field
for CO2 adsorption in non-Löwenstein zeolites. By
means of molecular simulations based on this force field, we showed
that the carbon dioxide adsorption efficiency in MFI is determined
by the number of Al atoms, rather than by their distribution in the
framework. 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 impact
on the heat of adsorption in MOR. Although structures with a very
high and very low number of non-Löwenstein bonds presented
significant differences, the bonds themselves do not affect the heat
of adsorption directly. Instead, we found that an homogeneous distribution
of the Al atoms in the sites forming the C-channel is more favorable.
Finally, the small-pore distribution of the ITW zeolite led to high
values of the heat of adsorption and wide error bars, which made the
study feasible just for low aluminum concentrations. In that case,
we report a small dependency of the heat of adsorption on the Al distribution.