First-Principles Molecular Dynamics Simulations of Ammonia Adsorption onto MFI Zeolite Nanosheets

MFI zeolite nanosheet membranes are promising candidates
for ammonia
separation from nitrogen and hydrogen gases, yet questions remain
on the origin of their high selectivity. Silanols, Si–OH, are
present in high concentration at the surface of zeolite nanosheets,
and force-field-based simulations indicate that surface adsorption
at the silanols contributes to selectivity. Acidic silanol groups
can chemically react with ammonia via transfer of a proton to form
ammonium ions, which may further contribute to the ability of zeolite
nanosheet membranes to separate ammonia from other gases. In this
work, we used first-principles molecular dynamics techniques to simulate
ammonia’s behavior within stacked MFI zeolite nanosheets. We
found that at 523 K and a loading corresponding to 35 bar, conditions
desired for the ammonia separation, about 30% of ammonia reacts with
surface silanols. Our work explored H-bonding and proton transfer
within this system.