Isotopic transient

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... 

Meunier, F.C., Tibiletti, D., Goguet, A., Shekhtman, S., Hardacre, C., and Burch, R. 2007. On the complexity of the water-gas shift reaction mechanism over a Pt/Ce02 catalyst Effect of the temperature on the reactivity of formate surface species studied by operando DRIFT during isotopic transient at chemical steady-state. Catal. Today 126 143 17. 

The method of isotopic transient reaction kinetics (see 5), applied in a chemical steady state is an elegant application of the true steady state measurement. 

Shen et al. (142) used an isotopic transient technique and XPS to investigate the partial oxidation of CH4 to synthesis gas on a Ni/Al203 catalyst at 973 K. The results show that CH4 can decompose easily and quickly to give H2 and Ni C on the reduced catalyst, and that Ni vC can react rapidly with NiO, formed by the oxidation of nickel by 02 to give CO or C02, depending on the relative concentration of Ni,C around NiO on the catalyst surface. The conclusion drawn by the authors (142) was not only that H2 and CO are primary products in the partial oxidation of CH4, but also that most of the CO2 is also the primary product of the surface reaction between Ni,C and NiO. In contrast, the kinetics results of Verykios et al. (143) indicated that the reaction on the Ni/La203 catalyst mainly takes place via the sequence of total oxidation to CO2 and H20, followed by... 

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. 

Mirodatos, C., Use of isotopic transient kinetics in heterogeneous catalysis, Catal. Today 1991, 9 (1-2), 83-95. 

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 ... 

In a recent review work (117) on the chemical and nano-structural characterization of NM/CeO catalysts, a detailed study of the H interaction with a Pt/CeO catalyst reduced at temperatures ranging fh)m 473 K to 773 K is reported. The experimental techniques used in this work were TPD-MS and Isotopic Transient Kinetics (ITK) of the H2/D2 exchange at 298 K. The catalyst sample was carefully selected in order to minimise the Pt and support sintering effects in the investigated range of reduction temperatures. Likewise, a chlorine-free metal precursor, [Pt(NH3)4](OH)2, was used in the preparation of the catalyst. 

Various improvements have broadened the research in the held of zeoUte membranes and films, such as the development of new synthesis procedures, the use of new supports with speciUc characteristics (monoliths, foams, etc.) or the use of modified supports by means of masking or grafting techniques, the appUcation of new analytical techniques (isotopic-transient experiments, permporometry, etc.), the control of the orientation of the crystals (by means of covalent Unkages, synthesis conditions, etc.) and of the thickness of the membranes, and the preparation of new zeolites as membranes or new zeoUte related-materials. In addition, a variety of zeoUtes can now be prepared as coUoidal systems with particle dimensions ranging from tens to a few hundred nanometers. 

XPS (x-ray photoelectron spectroscopy) utilizes photoionization and energy-disperse analysis of the emitted photoelectrons to study the composition and electronic state of a region of the surface of a zeolite. However, aU these techniques are destructive ones, and for that reason other methods such as isotopic-transient experiments or reflectance [16] and fluorescence [17] imaging can be used to estimate the effective membrane thickness. 

There are macroscopic (uptake measurements, liquid chromatography, isotopic-transient experiments, and frequency response techniques), and microscopic techniques (nuclear magnetic resonance, NMR and quasielastic neutron spectrometry, QENS) to measure the gas diffusivities through zeolites. The macroscopic methods are characterized by the fact that diffusion occurs as the result of an applied concentration gradient on the other hand, the microscopic methods render self-diffusion of gases in the absence of a concentration gradient [67]. 

Bowen TC, Wyss JC, Noble RD, and Falconer JL. Measurements of diffusion through a zeohte membrane using isotopic-transient... 

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. 

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