High-Throughput Calculation Of The Distribution And Necessity Of Heteroatoms In Zeolites

Zeolites are a class of crystalline microporous materials comprised of cornersharing TO4 tetrahedra(T: tetrahedrally coordinated Si,Al,P,Ge for example).Owing to the good thermal stability,high surface area,unique pore system,and tunable composition and acidity,zeolites have been widely used in many important physical and chemical processes,such as adsorption,separation,and shape-selective catalysis.To accelerate the discovery of new zeolitic materials,millions of hypothetical zeolite structures have been predicted via various computational methods.Furthermore,many structure evaluation criteria have been proposed to predict the feasibility of the hypothetical structures.However,the function-oriented realization of these hypothetical still faces many major challenges,including the predictions of their properties(i.e.adsorption,separation,and catalysis)and synthesis conditions.Given that the introduction of heteroatoms is closely related with the properties and realization of hypothetical zeolites,it is of great significance to study the rational distribution of heteroatoms and their necessity in synthesis.First,the unique properties of zeolites such as adsorption,catalysis and ionexchange of zeolites are largely originated from the introduction of heteroatoms.To correctly predict such properties,one need the detailed information of the distribution of heteroatoms.Systematic study of heteroatom distribution will thus help the selection of hypothetical zeolites with excellent functionalities for function-oriented discovery of new zeolitic materials.In addition,such study will also help to understand the mechanism behind the adsorption and catalytic processes of known zeolites.However,systematic studies of heteroatom distribution in zeolites are scarce,current theoretical studies are mostly focused on the preferential locations for the introduction of single heteroatoms in the unit cell of zeolites.When multiple heteroatoms are required,conventional approaches consider only symmetrically related T sites to reduce the computation complexity.Such symmetry-constrained approaches obviously overlooked many possible configurations.On the other hand,with the promising zeolite candidates selected,their synthesis is also quite complicated.The realization of zeolites is influenced by many factors,involving framework constituent elements,structuredirecting agent,reaction gel composition,reaction temperature and pressure,etc.Unfortunately,all predictions reported so far cannot provide effective information to guide the high-throughput synthesis of theoretical structures.For example,no highthroughput models have been proposed so far to predict the necessity of heteroatoms in experimental realization.Focusing on the distribution of heteroatoms and their necessity in synthesis,the main results are summarized as follows:(1)We conduct a systematic study in the distribution of two Ti atoms in the unit cell of titanosilicate zeolite BEA.Different from conventional symmetry-constrained approaches,the two Ti atoms are introduced into the BEA framework without any constraint.We adopt a symmetry-adapted algorithm to enumerate all possible configurations for double-Ti introduction.This approach searches the whole configuration space and excludes duplicated configurations,allowing a highthroughput and systematic investigation in Ti-distribution.We investigate 273 distinct double-Ti configurations and analyze the Ti-distribution via Boltzmann statistics.We find that many of the configurations overlooked by conventional symmetry-constrained approach indeed exhibit more feasible energies.Our study indicates the necessity of unconstrained introduction of Ti atoms when multiple-Ti atoms are considered for calculations.These results will also provide guidance on the understanding of catalytic mechanism and help the design of active titanosilicate zeolite catalysts.(2)We conduct a systematic study on Al distribution in hypothetical aluminosilicate zeolites.When concerning the introduction of many Al atoms in zeolite frameworks,previous studies only considered very limited structures without the systematic investigation on Al distribution.A total of 225,000 aluminosilicate structures are generated with Al randomly substituting Si in 375 hypothetical ABC-6 structures under different Si/Al ratios.Results show that the distribution of Al in lowenergy structure are more uniformly dispersed.While for high-energy structures,much denser distribution of Al atoms can be observed.By enumerating numerous Alintroduced structures,the Al atoms in low-energy structures obtained in our study are more rationally distributed.Further study of adsorption and catalytic properties will provide more accurate predictions on these structures,providing synthetic candidates for function-oriented realization of zeolites.(3)We propose for the a high-throughput approach to estimate the probability of a hypothetical structure being realizable as pure Al PO or heteroatom-stabilized Al PO zeolites.This approach is based on the Mahalanobis distances between hypothetical structures and their neighboring reference structures in framework distortion–energy plots.The advantage of this approach is that all zeolite frameworks are considered as pure Al PO polymorphs without building many heteroatom-containing models,which greatly reduces the computational expense and making this approach suitable for highthroughput structure evaluation.A test on 75 known Al PO structures showed that 82.6% of the known pure Al POs and 85.7% of the heteroatom-stabilized Al POs were correctly categorized using our approach.Owing to its high efficiency and reliability,our approach can be used for high-throughput structure evaluation of millions of hypothetical zeolite structures generated so far,providing important guidance toward the discovery of new Al PO zeolites.Our results will provide important guidance for the prediction of the physicochemical properties of hypothetical zeolites to help select promising candidates with excellent adsorption and catalytic properties.Our results on the necessity of heteroatoms will also guide the synthesis of hypothetical zeolites.Our results will provide important guidance for the discovery of new zeolitic materials.