👤 Ekaterina G. Ragoyja

ABSTRACTTo understand the nature of heterogeneous catalytic processes and improve their efficiency, it is necessary to conduct both experimental and theoretical studies. At the same time, there is no unified approach to obtaining the necessary data using quantum chemistry methods. In this work, problems of the existing calculational approaches are analyzed. The obtained information is used to develop the original three‐layer embedded cluster model approach, which is shown to be the most effective. The general algorithm for obtaining such models for various oxides is formulated. The sufficient accuracy of the proposed models in predicting geometric and energy characteristics, vibrational frequencies, activation barriers, and thermodynamic characteristics is verified. The specifics of calculating the thermodynamic characteristics of heterogeneous processes using the proposed cluster models is studied in detail. The developed approach is an effective tool for studying the mechanism of heterogeneous catalytic processes both by itself and in combination with experiment. Show less

A feasible, fast and reliable method for estimating ion association constants in PVC plasticized membranes of ion-selective electrodes from potentiometric data has been theoretically and experimentally substantiated. The method is based on the established fact of complete dissociation of salts of quaternary ammonium cations R4N + An‒ (except for those containing methyl substituents at the nitrogen atom) in a membrane plasticized with o-nitrophenyl octyl ether (o-NPOE). Therefore, the boundary potential at the interface of the membrane with an aqueous solution of R4N+ depends only upon the concentrations of the corresponding solution and the ion exchanger in the membrane and is independent of the presence of a lipophilic ionic additive (LIA), which makes it possible to use such ions as reference ones in the internal filling solution. If the ions studied (i+) are capable of forming ion associates with the ion exchanger, then the introduction of LIA into the membrane will lead to a decrease in the concentration of free i+ ions and to a corresponding increase in the boundary potential, from which the ion association constant can be directly calculated. The results obtained agree with the known literature data and the results of quantum chemical calculations. The prospective of applying the proposed method to the study of other membrane compositions is discussed. Show less

A critical analysis of the known theories of functioning of H+-selective electrodes (H+-SEs) based on neutral amine-type carriers is given. A model of specific ion association is proposed, according to which, in membranes plasticized with 2-nitrophenyloctyl ether, the protonated ionophore and cation-exchanger form much stronger ion pairs with inorganic ions extracted from the sample solution than with each other, and simple equations that describe the lower and upper limit detection (pHUDL and pHLDL) are obtained. A feasible and reliable method for quantifying the pKa values of ionophores in the membrane phase from potentiometric data is substantiated. The efficiency of using single-ion partition coefficients and ion pair formation constants for a priori quantitative description of the H+-SE response in solutions of various compositions has been demonstrated for the first time. It is shown that the width of the dynamic response range of such electrodes depends on the nature of the tertiary amino group, and the reasons for the observed effect are discussed. Show less