Isotopic tracing study of K promotion of NH3 synthesis on Ru

Nwalor, J.; Goodwin, James G.

doi:10.1007/bf01492282

Cited by 25 publications

(14 citation statements)

References 35 publications

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“…Nwalor and Goodwin determined that promotion of Ru/SiO 2 with K created a new additional type of site that was very active [47]. McClaine and Davis suggested that both the Cs-Ru/MgO and Ru/SiO 2 catalysts contained a relatively uniform site distribution [10].…”

Section: Discussionmentioning

confidence: 98%

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Isotopic transient analysis of ammonia synthesis over Ru/MgO catalysts promoted by cesium, barium, or lanthanum

Siporin

2004

Journal of Catalysis

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Section: Discussionmentioning

confidence: 98%

“…Ammonia synthesis catalyzed by both Fe [46] and Ru [10,28,47] has been studied previously with SSITKA. This technique is very powerful because it allows for the characterization of a catalyst surface under working conditions.…”

Section: Introductionmentioning

confidence: 99%

Isotopic transient analysis of ammonia synthesis over Ru/MgO catalysts promoted by cesium, barium, or lanthanum

Siporin

2004

Journal of Catalysis

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“…This has been further developed by Goodwin and coworkers into the state-of-the-art steady-state isotopic transient kinetic analysis (SSITKA) method [168][169][170]. In numerous studies, SSITKA was applied to determine in situ the microkinetics and to detect the reaction intermediates in heterogeneously catalyzed reactions (cf.…”

Section: Isotopic Transient Kinetic Experimentsmentioning

confidence: 99%

Transient Catalytic Studies

Hinrichsen

2008

Handbook of Heterogeneous Catalysis

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The Importance of Transient Catalytic StudiesThe concept of using transient operations dates back to the late 1930s and the preliminary investigations conducted by Wagner and Hauffe [1,2]. Later, during the 1960s, Tamaru contributed substantially to this field in heterogeneous catalysis, in particular, by the use of the method of transient response [3] and by introducing the isotopic labeling technique [4]. Since then, transient methods have become standard tools for unraveling heterogeneously catalyzed reactions; for details, see the reviews in Refs. [5][6][7][8][9][10], monographs [11,12], and a special edition of Applied Catalysis [13]. The reasons for the wide application of transient methods are manifold. In chemical reactions, generally speaking, if the rate (rate equation, rate constant, and activation energy) of each of the elementary steps which comprise the overall reaction is known, the (micro)kinetics of the overall reaction may be understood. To take a simple example, in the reaction between hydrogen and bromine, the kinetics of the overall reaction follows a rather complicated rate law:However, if all the elementary reactions in the overall reaction are known, the kinetic behavior of the overall reaction may be explained on the basis of the rate constants, and the activation energies of the forward and backward reactions of the following elementary steps:In the case of such gas-phase reactions, the rate constants and activation energies of each of the elementary steps are independent of the concentration of reactants, reaction products, and reaction intermediates. This approximately also holds for reactions in solution.In the case of heterogeneously catalyzed reactions, the properties of the catalyst depend upon the concentrations of reactants, reaction intermediates, reaction products and, in some cases, spectator species that do not participate in the reaction path but which are chemisorbed on the catalyst surface. Furthermore, in many cases surface restructuring may occur along with the adsorption, and this results in marked changes in the reactivity of the surface. Consequently, even if the catalyst surface is kept in a well-defined state at the outset, as examined ex situ using a variety of spectroscopic techniques, it can be markedly different during the progress of reaction, and especially under industrially relevant reaction conditions. For example, in the case of oxide catalysts the extent of oxidation of the catalyst surface during the redox reaction is also influenced by the relative ratio of the rates of reduction and oxidation. This results in prominent changes in the properties of catalyst surfaces, depending upon the relative concentration of the reactants and the reaction temperature. In the case of acid catalysts, the acidity of the working catalyst surface (which should be associated with the catalytic activity) is that under the reaction conditions, and not that under the conditions far from those prevailing in the actual reaction.In the case of heterogeneous catalysis the rate co...

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“…Ammonia synthesis occurs by a relatively simple (6.57) Given the decrease in volume of the products and its high exothermicity, the reaction is thermodynamically favorable at high pressures and low temperatures as shown in Figure 6.17a. The same metals promoted with K or Cs are substantially more active; indeed, addition of K increases TOF values for Fe and Ru/MgO by factors of 5-1 0 and 15-30, respectively, under the same low pressure conditions (Dumesic and Trevifio, 1989;Nwalor and Goodwin, 1994;. It must be able to adsorb and dissociate N2 to nitrogen atoms at relatively mild conditions, a challenge considering the large dissociation energy of N2.…”

Section: Reaction Chemistry Thermodynamics Kinetics and Mechanismmentioning

confidence: 99%

“…More recently, demonstrated that .70 provides an excellent fit of kinetic data over a wide range of reaction conditions using the constants listed in Table 6.13. For example, Nwalor and Goodwin (1994) studied the kinetics and mechanism of ammonia synthesis on Ru/K/SiO2 and I3 valid at 400°C, 2 atm, an H2N2 ratio of 3, obtained the following rate equation: r = WN, PH* PNH, and a GHSV of 5,000-23,000 h-I. Most of the rate expressions for ammonia synthesis on Fe (Table 6.13) incorporate the partial pressure of NH3 in the denominator, indicating that the rate is inhibited by NH3.…”

Section: Reaction Chemistry Thermodynamics Kinetics and Mechanismmentioning

confidence: 99%