Bridging the pressure and material gap in the catalytic ammonia oxidation: structural and catalytic properties of different platinum catalysts

Baerns, M.; Imbihl, R.; Kondratenko, Vita A.; Kraehnert, Ralph; Offermans, WK Willy; Santen, van Ra Rutger; Scheibe, A.

doi:10.1016/j.jcat.2005.03.002

Cited by 84 publications

(84 citation statements)

References 31 publications

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“…4. The formation of these products started above 473 K. The amount of formed H 2 O achieved a maximum at 573 K. A further temperature increase led to a decrease of the amount of H 2 O; it increased, however, again after passing through a minimum between 773 and 873 K. The formation of 14 N 2 and H 2 increased with temperature in accordance with an increased degree of NH 3 decomposition over oxygen-treated Pt gauze as reported by us previously [26]. The increase in the amount of 14 N 2 is the main product at higher temperatures.…”

Section: Reduction Of Nitric Oxide By Ammoniasupporting

confidence: 85%

“…The importance of oxygen species for the ammonia activation has been stressed in recent investigations [18,22,26]. Considering these results it may be derived that the initial steps of NH 3 interaction with NO under conditions studied cannot be ascribed to ammonia dissociation, as predicted by previous mechanistic concepts [3][4][5][6][7][9][10][11][12].…”

Section: Primary Reaction Steps Of Nh 3 and No Interactionmentioning

confidence: 67%

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Mechanistic insights into the formation of N2O and N2 in NO reduction by NH3 over a polycrystalline platinum catalyst

Kondratenko

Baerns

2007

Applied Catalysis B: Environmental

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The reaction pathways of N 2 and N 2 O formation in the direct decomposition and reduction of NO by NH 3 were investigated over a polycrystalline Pt catalyst between 323 and 973 K by transient experiments using the temporal analysis of products (TAP-2) reactor. The interaction between nitric oxide and ammonia was studied in the sequential pulse mode applying 15 NO. Differently labelled nitrogen and nitrous oxide molecules were detected. In both, direct NO decomposition and NH 3 -NO interaction, N 2 O formation was most marked between 573 and 673 K, whereas N 2 formation dominated at higher temperatures. An unusual interruption of nitrogen formation in the 15 NO pulse at 473 K was caused by an inhibiting effect of adsorbed NO species. The detailed analysis of the product distribution at this temperature clearly indicates different reaction pathways leading to the product formation. Nitrogen formation occurs via recombination of nitrogen atoms formed by dissociation of nitric oxide or/and complete dehydrogenation of ammonia. N 2 O is formed via recombination of adsorbed NO molecules. Additionally, both products are formed via interactions between adsorbed ammonia fragments and nitric oxide. #

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Section: Reduction Of Nitric Oxide By Ammoniasupporting

confidence: 85%

Section: Primary Reaction Steps Of Nh 3 and No Interactionmentioning

confidence: 67%

Mechanistic insights into the formation of N2O and N2 in NO reduction by NH3 over a polycrystalline platinum catalyst

Kondratenko

Baerns

2007

Applied Catalysis B: Environmental

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“…Catalytic etching of Pt catalysts during ammonia oxidation was not detected at pressures below 15 Pa even after extended periods of catalyst operation [9,10], an observation confirmed by our recent study on the influence of pressure on structural and catalytic properties of different platinum catalysts [11]. At higher reactant partial pressures (kPa range), the reconstruction of Pt surfaces has been studied during catalytic ammonia oxidation at temperatures above 600 8C on polycrystalline platinum in the shape of wires [4,6,7,12], gauzes [5,13,14], and spheres [15].…”

Section: Introductionsupporting

confidence: 76%

“…The reactor has been described earlier in detail [11,25]. It allowed measurements with minimal blank activity up to 700 8C, while the kinetic regime prevailed up to ca.…”

Section: Catalytic Testsmentioning

confidence: 99%

“…Suitable tools to study the highly exothermic ammonia oxidation are microstructured reactors as proposed by Rebrov et al [23,24] for supported Pt/Al 2 O 3 , and recently established by our group for catalytic investigations on polycrystalline Pt foils [11,25]. Applying the latter reactor that enabled temperature control in the reaction, product formation was recorded as a function of temperature and time.…”

Section: Introductionmentioning

confidence: 99%

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Morphology changes of Pt-foil catalyst induced by temperature-controlled ammonia oxidation near atmospheric pressure

Kraehnert

Baerns

2007

Applied Catalysis A: General

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Reaction-induced changes of the morphology of a Pt foil catalyst during ammonia oxidation were investigated in a temperature-controlled way for partial pressures of oxygen and ammonia around 4.5 and 3 kPa, respectively, and at temperatures between 20 and 700 8C. The presence of the feed mixture (ammonia and oxygen) was required to induce surface roughening. Moreover, the reaction temperature controlled the type of restructuring of the Pt surface, that is, either into rows of parallel facets where facet size increased with temperature, or as bulky microcrystals protruding from the surface. Surprisingly, reaction-induced surface faceting was already observed at 286 8C. Between 286 and 374 8C adsorbateenhanced surface diffusion of Pt is suggested to account for the surface restructuring well below temperatures reported for significant Pt transport through the gas phase via volatile PtO x .

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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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Bridging the pressure and material gap in the catalytic ammonia oxidation: structural and catalytic properties of different platinum catalysts

Cited by 84 publications

References 31 publications

Mechanistic insights into the formation of N2O and N2 in NO reduction by NH3 over a polycrystalline platinum catalyst

Mechanistic insights into the formation of N2O and N2 in NO reduction by NH3 over a polycrystalline platinum catalyst

Morphology changes of Pt-foil catalyst induced by temperature-controlled ammonia oxidation near atmospheric pressure

Transient Catalytic Studies

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