Steady state isotopic

Catalyst characterization and Mechanistic Studies 3.2.1 Steady-State isotopic tracing experiments... 

Burch, R., Shestov, A.A. and Sullivan, J.A. (1999) A steady-state isotopic transient kinetic analysis of the N0/02/H2 reaction over Pt/Si02 catalysts, J. Catal. 188, 69. 

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. 

In this contribution, the steady-state isotopic transient kinetic analysis-diffuse reflectance Fourier transform spectroscopy (SSITKA-DRIFTS) method provides further support to the conclusion that not only are infrared active formates likely intermediates in the water-gas shift (WGS) reaction, in agreement with the mechanism proposed by Shido and Iwasawa for Rh/ceria, but designing catalysts based on formate C-H bond weakening can lead to significantly higher... 

During steady-state isotopic transient kinetic analysis, the 12CO was switched to 13CO and the carbon-containing adsorbed and gas phase species were monitored in the IR as they exchanged from the 12C to the 13C label. Particular attention was made to those species that exchanged on a timescale similar to that of the exchange of the product C02, as that species could be a likely intermediate to the water-gas... 

Jacobs, G., Crawford, A.C., and Davis, B.H. 2005. Water-gas shift Steady state isotope switching study of the water-gas shift reaction over Pt/ceria using in-situ DRIFTS. Catal. Lett. 100 147-52. 

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. 

Information on the steps in a reaction mechanism can be extended significantly by isotopic tracer measurements, especially by transient tracing [see Happel et al. (54,55)]. Studies by Temkin and Horiuti previously referenced here have been confined to steady-state isotopic transfer techniques. Modeling with transient isotope data is often more useful since it enables direct determination of concentrations of intermediates as well as elementary step velocities. When kinetic rate equations alone are used for modeling, determination of these parameters is more indirect. 

The application of the index-lake method presented here is only for lakes that are at hydraulic and isotopic steady states. A lake s steady-state isotopic composition is determined by the long-term averages of 8a, 8P, h, P, E, and water and air temperatures, which can vary greatly by the day and season and can vary to some degree annually. Therefore, it is only proper to apply the index-lake method to lakes of similar hydraulic residence time, during which time the averages of these controlling factors are determined. 

Reliable estimates of relative humidity are critical for use of the isotope mass-balance method however, humidity data are difficult to interpret and commonly not available for a specific study area. The index-lake method provides a means for checking the accuracy of these data and the validity of their use in isotope hydrology. The equation that describes the steady-state isotopic composition of a lake (35) is... 

Figure 4.3.1a shows a schematic of an apparatus to perform the steady-state, isotopic transient kinetic analysis for the hydrogenolysis of ethane over a Ru/Si02 catalysis ... 

Cerling recognized that 2 and C02 can be described in terms of their own production and tranport models, and that the isotope ratio of CO2 at any soil depth is described simply by the ratio of the and the models. For the purposes of illustration here, if we assume that the concentration of can be adequately described by that of total CO2 and that CO2 is produced at a constant rate over a given depth L, then the model describing the steady-state isotopic ratio of CO2 at depth z is (see Cerling and Quade (1993) for the solution where the above assumptions are not applied)... 

Steady-state isotopic transient kinetic analysis can determine the concentration and relative strength distribution of active sites. 

Buyevskaya et al, 1994 Mallens et al, 1994) and SSITKA (Steady-State Isotopic Transient Kinetic Analysis) (Nibbelke et al, 1995) techniques. It was demonstrated that ethane—the primary OCM product—is leaving the reactor with the same characteristic time as an inert tracer. This surely indicates that no intermediates noticeably residing on the surface participate in its formation. 

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... 

The study of the fixed-charge hypothesis is ideally carried out by steady-state isotopic permeability experiments. These conditions are impossible to meet in the study of hydroxyl ion movements. Furthermore, net OH" movements necessarily involve pH changes by their nature. Nevertheless, the experiments reported here can be used to determine the effects of external pH on OH" permeability since temperature and... 

A large amount of N2O was formed from the initial stage over LaM03 (M = Co, Mn, Fe, Cr, Ni) at 573 K. The time course of the NO+CO reaction (performed in a batch recirculation system) reflects this situation. These results support a two-step reaction pathway in which N2O is an intermediate for nitrogen formation, deal et al. (1994) confirm the role of N2O as intermediate in this reaction over perovskite oxides. They used steady-state isotopic transient kinetic analysis to study the mechanism of NO + CO reaction over LaCo03. They concluded that N2O was an intermediate in the formation of N2 at T < 873 K. They also concluded that at high temperature CO2 desorption became the rate-limiting step of the overall reaction. This is likely due to the rapid formation and slow decomposition of very stable carbonates on the perovskite surface as reported by Milt et al. (1996). 

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 SSITKA (steady-state isotopic transient kinetic analysis) developed and actively applied by Happel, Biloen and Goodwin, it is common to consider the catalyst surface to be composed of a system of interconnected pools, also termed compartments, where each pool represents a homogeneous or well-mixed subsystem within the reaction pathway. 

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