Transition State Shape Selectivity in Theoretical Prognosis for Zeolites Catalytic Activities on Example of Reaction Between Acrylonitrile and Piperylene.

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]