Insight into the structure of the heulandite-type zeolite containing aromatic compounds using periodic density functional theory

The heulandite-type zeolite (HEU) is an important class of naturally occurring zeolite materials. The recent development of a synthetic HEU zeolite with a high Si/Al ratio opens new possibilities for various applications. Herein, a periodic density functional theory with dispersion correction scheme (DFT-D3) was performed on the HEU-type zeolite. Various aspects of zeolite properties, such as the distribution of Al atoms within the zeolite framework, the prediction of the non-Lowenstein structure, and the presence of aromatic compounds within the cavity, were investigated. Calculation of the initial HEU framework shows that the Al atoms occupy the T2 and T3 sites in the most stable structure. Additionally, a non-Lowenstein structure was predicted for the first time to give a relatively stable HEU structure containing the Al-O-Al configuration. The preferred location of various aromatic compounds, namely, benzene, toluene and naphthalene, could be modeled in the 10-member ring channel to represent a host-guest system in this zeolite with a Si/Al ratio of 10. The results exemplify the importance of understanding the crystal structure of zeolites and the effect it has because of the presence of Al atoms and adsorbate molecules within the zeolite frameworks.