Steady-state isotopic transient kinetic analysis SSITKA

Rothaemel, M., Hanssen, K.F., Blekkan, E.A., Schanke, D., and Holmen, A. 1997. The effect of water on cobalt Fischer-Tropsch catalysts studied by steady-state isotopic transient kinetic analysis (SSITKA). Catal. Today 38 79-84. 

Ocal, M Oukaci, R Marcelin, G. Steady state isotopic transient kinetic analysis (SSITKA) investigation of NO reduetion with CO over perovskite eatalysts. Ind.Eng. Chem. Res., 1994, Volume 33, 2930-2934. 

Kinetics and diffusion Steady-state isotopic transient kinetic analysis (SSITKA) Temporal analysis of products (TAP) Tapered element oscillating microbalance (TEOM) Temperature scanning reactor (TSR) Zero length chromatography (ZLC) Pulsed field gradient NMR... 

Steady-state isotopic transient kinetic analysis (SSITKA) involves the replacement of a reactant by its isotopically labelled counterpart, typically in the form of a step or pulse input function. Producing an input function with isotope-labelled reactants permits the monitoring of isotopic transient responses, while maintaining the total concentration of labelled plus nonlabelled reactants, adsorbates, and products at steady-state conditions. It is assumed that there are no effects due to differences in kinetic behavior of the isotopic species from unmarked atomic species. However, for instance, deuterium substitution exhibits isotopic effects that can not be neglected. 

In the present communication we report on the influence of water on the FT synthesis studied by SSITKA and conventional kinetic experiments. Steady-state isotopic transient kinetic analysis (SSITKA) has proved to be a powerful technique for this work. The technique involves switching between CO and " CO in the feed gas and analyzing the transients with respect to the formation of products containing C and C. This technique allows the determination of the true turnover frequency of the active site, decoupled from site coverage. Applied to the FTS over metal promoted cobalt catalysts SSITKA has shown that the true turnover frequency of cobalt always remains the same, regardless of the second metal [6-8]. 

Steady-state isotopic transient kinetic analysis (SSITKA) shows that the deactivation of the methanation reaction after water treatment is due to a decrease in the number of active sites, while the intrinsic site activity apparently remains unchanged. 

The greater activity of Pd for methanol decomposition reaction was also found by using the steady state isotopic transient kinetic analysis (SSITKA) method over noble metal (Pt, Pd, Rh)/ceria catalysts. Their activity increased in the order Rh < Pt < Pd, while the by-products were (i) methane, carbon dioxide, water, methyl formate and formaldehyde in most cases and (ii) ethylene and propylene, formed only over Rh/Ce02, at 553 K. SSITKA measurements indicated that two parallel pools exist for the formation of CO (via formation and decomposition of formaldehyde and methyl formate). The difference in the activity order of noble metal/ceria catalysts seems to correlate with the surface coverage of active carbon containing species, which followed the same order. The latter implies that a part of these species is formed on the ceria surface or/and metal-ceria interface. ... 

In some cases the so-called "Steady-State Isotopic Transient Kinetic Analysis" (SSITKA) was used for detailed investigations of reaction mechanisms. Shannon and Goodman [123] present an extensive review of this subject. Hinrichsen et al. [124] employed temperature programmed desorption to study the ammonia synthesis on ruthenium catalysts. 

Study of the dynamics of isotope transfer under steady-state reaction conditions, the so-called steady-state isotopic transient kinetic analysis (SSITKA), is successfully employed in the investigation of different physical and... 

Pulse intensities in vacuum experiments range from 10 to 10 molecules per pulse with a pulse width of 250 ps and a pulse frequency of between 0.1 and 50 pulses per second. Such a spectrum of time resolution is unique among kinetic methods. Possible experiments include high-speed pulsing, both single-pulse and multipulse response, steady-state isotopic transient kinetic analysis (SSITKA), temperature-programmed desorption (TPD), and temperature-programmed reaction (TPR). 

Temperature-prograimned reduction, oxidation and desorption (TPR, TPO, TPD), belong probably to the most widely used in situ techiuques for the characterization of oxidation catalysts and are discussed in more detail in Section 19.4. While TPD (with ammonia as the probe molecule) is frequently used to examine surface acid sites, TPR and TPO (with H2 or O2, respectively) provide information on the redox properties of oxide catalysts being crucial for their performance in catalytic oxidation reactions. Important information on reaction mechanisms can be obtained when the catalysts are heated in the presence of reactants combined with mass spectrometric product analysis. This is called temperature-programmed reaction spectroscopy (TPRS). As far as reaction mechanisms and kinetics are concerned, transient techniques which reflect the response of the catalytic system to a sudden change of reactant are inevitable tools. Two such techiuques, namely the temporal analysis of products (TAP) reactor and steady-state isotopic transient kinetic analysis (SSITKA) will be described in more detail in Section 19.5. 

Steady-state isotopic transient kinetic analysis (SSITKA)... 

However, the carbonate mechanism is favored by some authors. Using a combination of DRIFTS and steady-state isotopic transient kinetic analysis (SSITKA) Meunier et al. assessed the reactivity of the species formed at the surface of an Au/Ce(La)02 catalyst during the WGS reaction. The analysis revealed that surface formates are not important factors in the WGS reaction mechanism. Their role is ascribed to minor reaction intermediates but not spectators because they nevertheless participate in the formation of reaction product. 

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