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While organic structure directing agents (OSDAs) are well known to have adirectional influence on the topology of a crystallizing zeolite, therelationship between OSDA charge and siting of aliovalent ions on a primarilysiliceous framework is unclear. Here, we explore the relationship between OSDAorientation, Al3+ siting, and lattice energy, taking as a model system CHAzeolite occluded with N,N,N-trimethyl-1-adamantyl ammonium (TMAda+) at an Si/Alratio of 11/1. We use density functional theory calculations to parametrize afixed-charge classical model describing van der Waals and electrostaticinteractions between framework and OSDA. We enumerate and explore all possiblecombinations of OSDA orientation and Al location (attending to Lowenstein'srule) within a 36 T-site supercell. We find that interaction energies vary over60 kJ/double-six-ring-unit (d6r). Further, analysis of configurations revealsthat energies are sensitive to Al-Al proximity, such that low energies areassociated with Al3+ pairs in 8-membered rings and higher energies associatedwith Al3+ pairs in smaller 6- and 4-membered rings. Comparisons with Al sitinginferred from CHA zeolite crystallized with TMAda+ suggests that these computedinteraction energies are useful reporters of observed Al siting in CHAsynthesized with TMAda+.

Influence of N,N,N-trimethyl-1-adamantyl ammonium (TMAda+) Structure Directing Agent on Al Pair Distributions and Features in Chabazite Zeolite