Mass Spectrometry in the SSITKA studies
||Mass Spectrometry Handbook
A John Wiley and Sons, Inc.. 2012.
28 c. ISBN 9780470536735.
||Isotope transient kinetics in mass transfer processes, MS in SSITKA studies, and kinetics of fast chemical reactions, SSITK, at atmospheric pressure under selected reactor types, SSITKA for discrimination of reaction mechanisms, SSITKA, surface concentration and chemical identity of active intermediates
Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russian Federation
This review includes a discussion of the general principles of SSITKA as well as the experimental and theoretical approaches that are used to study the isotopic transient kinetics, reactions of label transfer as applied to the problem to be solved. The dynamic features of the experimental setup that includes the stepwise disturbing system of feed gas flows, catalytic reactors and mass-spectrometric analysis are considered in detail. As a result, the reactor and mass-spectrometers that are most convenient for dynamic isotopic studies were selected. The theoretical study of isotopic transient kinetics allowed for the separation of five basic reaction pathways which serve as elementary “bricks” to build virtually any reaction mechanism. It is shown that the key features of the reaction mechanism can be revealed directly from the shape of isotope response curves, while the detailed characteristics can be derived from numerical modeling by fitting the experimental data with calculated ones.
By the example of various catalytic reactions (ethylene epoxidation over Ag, deNOx with methane on Co-ZSM-5, Fischer-Tropsch synthesis over Co-based systems) we show how the reaction mechanism was revealed and the concentrations of key intermediates and reaction rate coefficients were estimated using different isotope labels (18O, 15N, 13C etc.). A single instance of transient isotopic kinetic study for the evaluation of mass transfer parameters of NO and water diffusion into the bulk of Pt-containing fiberglass catalyst is discussed. Our experience helped to elucidate the mechanism of oxygen transport in oxides with perovskite and fluorite lattice at high temperatures (up to 900C). All kinetic parameters including the diffusion coefficients were obtained. The probability of H/D exchange for quantification of Brønsted acidity in fiberglass materials is also discussed.