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Based on transition state shape selectivity (TSSS) conception, as general model, we have evaluated the zeolites topology influence on the reaction rate of acrylonitrile with piperylene. Theoretical modeling was carried out for the set of zeolites with cavities diameters: KA (3 Å), NaA (4 Å), CaA (5 Å), CaX (8 Å), NaX (9 Å). The estimated parameter was the "frozen" transition state (TS) adsorption energy in the cavities and its dependence on the diameter of the zeolite cavity. Also, we compared theoretical dependence with found in experiment dependence of the effective reaction rate constants (k, s−1) for reaction between acrylonitrile and piperylene in the presence of zeolite on the cavity diameter of zeolites. Both dependences have extremal character and maximum value of rate constant is observed for zeolite CaA with cavity diameter 5 Å. Thus, the effective rate of the product formation reaction in the absence of zeolites was 1.67 ∙ 10–4 s−1, and in the presence of zeolite CaA 3.23 ∙ 10–4 s−1. Thus, in the presence of zeolite, the reaction accelerated 1.9 times. Theoretical modeling prognoses the best transition state stabilization and, as consequences most energy activation decrease, at the same zeolite cavity diameter. This result is well explained by the comparability of the dimension of the TS and the cavity of the zeolite in which the reaction occurs. [ABSTRACT FROM AUTHOR]

We improved our previous theoretical method for prediction of the catalytic activity of porous materials, which is based on the concept of transition state shape selectivity. This method used adsorption energy calculations for transition state (TS) with «frozen» (only the placement of TS inside the pore is optimized) structure on porous materials with molecular mechanics (MM) as a calculational method. Our improvement consists of application of semi-empirical methods with dispersion correction (e.g., PM3-D3 or PM6-D3H4) instead of MM. We found that with semi-empirical methods adsorption energy dependences on pore diameter are similar to dependences obtained by MM, and also semi-empirical methods predict the same value of the cavity diameter, at which there is a maximum of TS adsorption energy. Despite these similarities in obtained results, semi-empirical methods have the advantages that they can more accurately describe structures, intermolecular interactions and energy values. We have shown that the level of theory (PM3-D3 or RI-MP2/ma-def2-SVP) used for TS structure search, in the case of suggested method, has little effect. [ABSTRACT FROM AUTHOR]