Molecular sieve manufacturer explains the impact of hydrocarbon conversion in molecular sieves on the activity of catalytic materials

One of the main challenges in simulating chemical reactions in molecular sieves is to accurately predict adsorption energy and reaction history maps of hydrocarbon conversion in microporous materials. The current choice for simulating the reactivity of complex catalytic materials is DFT. However, the commonly used density functional cannot accurately describe long-range dispersion interactions. The dominant interaction between hydrocarbon compounds and the inner wall of molecular sieves is a weak van der Waals interaction related to dispersion properties, so conventional DFT methods cannot accurately calculate it. This may not only lead to inaccurate calculation of the energy of chemical reactions, but also incorrectly predict the stability of the system or the trend of the reaction.
Among them, the effect of dispersion on the total stability energy of Reaction intermediate and Transition state is unevenly distributed along the direction of Reaction coordinate. It is worth noting that dispersion is an intermolecular correlation effect. The simplest method that can clearly describe the electronic structure related to electrons is the MP2 theory. However, when using MP2 to calculate periodic systems, it is only feasible when using small basis groups and very small unit cells containing only a few atoms.
Recently, an embedding scheme was proposed to incorporate local correction of post HF levels into DFT calculations to calculate periodic molecular sieve models. This method allows for accurate simulation of the structure and electrostatic properties of the molecular sieve reaction environment using periodic DFT calculations. Improvements have been made to the self interaction and van der Waals interaction between the adsorbed reactants and the inner wall of the molecular sieve. This is achieved by applying the decomposition identity integral approximation MP2 method and the cluster model embedded in the periodic model of molecular sieves, which can represent the essential part of the molecular sieve skeleton. The MP2: DFT method designed in this way is suitable for studying the reactions between small and medium-sized adsorbate molecules and very large chemical systems like molecular sieve crystals, and can also quantitatively calculate the reaction energy distribution of hydrocarbon conversion in microporous matrices at a near chemical accuracy level.
To illustrate this point, scientists have studied the interaction between isobutene and zeolite B acid centers as a case study of B acid catalyzed hydrocarbon conversion. Since this reaction is related to butene skeleton Isomerization reaction, it is not only very meaningful from a practical point of view, but also has attracted the attention of many theoretical researchers. This is because it involves a basic problem, that is, whether it is possible to form a stable Reaction intermediate - tert butyl Carbocation in the molecular sieve microporous matrix.
Some studies reported that DFT method was used to calculate the Protonation reaction of isobutene, and a rather small cluster model was used to simulate the local environment of the acid center of zeolite B. It is found that the relative stability of Protonation products is very dependent on the computational level, and more importantly, the size of the cluster model. When using the cluster model method, the only minimum point on the Potential energy surface corresponds to the alkoxy group bound by Covalent bond, while Carbocation exists in the transition form with a very short life. This study indicates that the conversion of hydrocarbons in molecular sieves does have a significant impact on the activity of catalysts. Hunan Providence New Materials Co., Ltd is a professional molecular sieve manufacturer which can provide USY zeolite, NaY zeolite, REY zeolite, ZSM-5 zeolite, welcome to consult.