Influence of the <i>N</i>,<i>N</i>,<i>N</i>-Trimethyl-1-adamantyl Ammonium Structure-Directing Agent on Al Substitution in SSZ-13 Zeolite

Abstract

Structure-directing agents (SDAs) influence not only zeolite structures but also the distribution of Al on zeolite lattices. The origins of this Al-directing influence are not well understood. Here, we use first-principles methods to explore the interactions between an N,N,N-trimethyl-1-adamantyl ammonium (TMAda+) OSDA and framework [AlO2]− in the dilute limit within an SSZ-13 lattice. Molecular dynamics and geometric and electronic structures illuminate the rotational freedom of TMAda+ OSDA within an SSZ-13 cage, the primarily electrostatic nature of its interactions with [AlO2]−, the effect of the solvent in screening the electrostatics, and the relative invariance of that interaction within a subset of Al locations within the same SSZ-13 major cavity. These results indicate that the Al distribution patterns observed in relevant SSZ-13 samples are not consequences of the location bias for Al substitution within a single TMAda+–cage complex but likely involve long-range electrostatics among multiple TMAda+–cage complexes. The computational protocol can be employed to examine other combinations of SDAs and zeotypes of interest.