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• 1
Electronic Resource
Springer
Topics in catalysis 1 (1994), S. vii
ISSN: 1572-9028
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology
Type of Medium: Electronic Resource
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• 2
Electronic Resource
Springer
Topics in catalysis 1 (1994), S. 169-176
ISSN: 1572-9028
Keywords: Surface oxygen transients ; kinetic modelling ; Zn(0001) surface
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology
Notes: Abstract In this paper is presented a model for the kinetics of gas adsorption at solid surfaces, in which transient formation is involved. In the case of ideal adsorption where the rate constants are independent of the surface coverages, the kinetics can be solved exactly in the framework of the first order kinetic law. The expression of the sticking coefficient for the final chemisorbed state is obtained in terms of the rate constants introduced in the model and compared to the expression commonly adopted in the literature. By means of a fitting procedure the kinetics were used to describe experimental data on the dioxygen adsorption at the Zn(0001) surface. An appropriate analysis of the fitting parameters, derived from adsorption data collected at different temperature of the substrate, allows for the activation energy of the processsurface transient → final adsorbed species to be estimated.
Type of Medium: Electronic Resource
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• 3
Electronic Resource
Springer
Topics in catalysis 1 (1994), S. 189-192
ISSN: 1572-9028
Keywords: catalysis research ; ammonia synthesis ; sulfuric acid ; catalyst characterization
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology
Type of Medium: Electronic Resource
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• 4
Electronic Resource
Springer
Topics in catalysis 1 (1994), S. 215-231
ISSN: 1572-9028
Keywords: ammonia synthesis ; surface structure ; structure sensitivity ; iron ; rhenium ; STM
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology
Notes: Abstract Ammonia synthesis is one of the most structure sensitive catalytic reactions. Reaction studies using single crystals showed the open (111) and (211) crystal faces of iron and the $$(11\bar 21)$$ and $$(11\bar 20)$$ crystal faces of rhenium to be most active, while the close packed iron (110) and rhenium (0001) crystal faces were almost inactive. These studies suggest that seven (C7) and eight (C8) metal atom coordinated surface sites, which are available only on the active surfaces, are very active for the dissociation of dinitrogen, the limiting factor in the reaction rate under most experimental circumstances. In this paper, the experimental evidence for the existence of the C7 sites in iron is reviewed. In addition, the role of potassium in creating a different active site which is less sensitive to the iron surface structure is discussed. Newly developed surface science techniques should permit investigations into the dissociation of dinitrogen at the C7 sites and how the resulting chemisorbed nitrogen atoms are removed to allow for reaction turnover. Advances in LEED-surface crystallography, allowing detailed determination of relaxation in the clean metal surfaces and adsorbate induced restructuring of the metal surface, reopen the question of the real structure of the active sites in the presence of atomic nitrogen, or atomic nitrogen coadsorbed with potassium and oxygen. Investigation of the dynamics of surface restructuring involving the movements of both the substrate metal atoms and the chemisorbed atoms by surface diffusion becomes feasible by the availability of the high pressure/high temperature STM system built in our laboratory. Studies of the surface structures of the model iron catalysts under dynamic conditions, using 0.1 ms time resolution and atomic spatial resolution under reaction conditions are now possible.
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• 5
Electronic Resource
Springer
Topics in catalysis 1 (1994), S. 265-271
ISSN: 1572-9028
Keywords: ammonia synthesis ; mechanism ; direct dissociation pathway ; surface science studies
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology
Notes: Abstract Consideration is given to the nature of the dissociation pathway of nitrogen on Fe, an important initial step in ammonia synthesis. In particular, the disagreement over the basic energetics of this process is discussed, that is whether the pathway involves direct or indirect (precursormediated) dissociation. It is concluded that under the conditions of industrial ammonia syn thesis the dominant process is direct, but that indirect dissociation may pertain under some experimental conditions.
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• 6
Electronic Resource
Springer
Topics in catalysis 1 (1994), S. 273-283
ISSN: 1572-9028
Keywords: ammonia synthesis ; temperature programmed adsorption ; temperature programmed desorption ; potassium promotion ; microkinetic modelling
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology
Notes: Abstract Iron catalysts with and without potassium promoter were studied in a combined temperature programmed reaction and flow micro reactor system connected to a mass spectrometer. The temperature programmed desorption (TPD) studies demonstrated a significant shift of the N2 peak to lower temperatures with the addition of K to the catalyst. The isobars suggested that this change can be interpreted as a destabilization of N-*. The N2 adsorption results were in good agreement with earlier studies of singly promoted catalysts. Thus the rate was found to be slow and activated. The rate constants were not in any disagreement with transition state theory. The addition of K had very little effect on the temperature programmed adsorption (TPA) curves, while for multiply promoted catalysts there was a significant shift to lower temperatures of the main adsorption dip. A microkinetic model for the NH3 synthesis reaction based on isobars for H2 and N2 and on the TPD results for N2 displayed a good agreement with many of the features of the experimental data. An interesting example is that the destabilization of N-* and NH-* by K can explain the difference in the promoting effect at high and low pressures. However, the conclusion is that a simple Langmuir type of kinetic model cannot result in a perfect fit of a reasonably extended experimental set of data.
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• 7
Electronic Resource
Springer
Topics in catalysis 1 (1994), S. 315-324
ISSN: 1572-9028
Keywords: surface science ; surface structure ; surface reactions ; dynamics ; calorimetry
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology
Notes: Abstract The rigour and wide ranging power of experimental surface science techniques developed in recent years has transformed our ability to understand surface processes. In this brief but broad ranging review, these developments are illustrated with examples of new results in: structure determination; calorimetric measurements of adsorption heats; kinetics and dynamics of adsorption and surface catalysed reactions; and the control of surface reactions.
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• 8
Electronic Resource
Springer
Topics in catalysis 1 (1994), S. 385-403
ISSN: 1572-9028
Keywords: ammonia synthesis ; microkinetic modeling ; surface science ; nitrogen dissociation ; dynamics ; adsorption induced changes
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology
Notes: Abstract The development of the understanding of catalytic reactions on metal surfaces in general and the ammonia synthesis reaction in particular is discussed. The paper will give a personal perspective on the discussions that took place at the meeting at Havreholm Hall in September 1993.
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• 9
Electronic Resource
Springer
Topics in catalysis 10 (2000), S. 1-1
ISSN: 1572-9028
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology
Type of Medium: Electronic Resource
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• 10
Electronic Resource
Springer
Topics in catalysis 10 (2000), S. 27-38
ISSN: 1572-9028
Keywords: nitrous oxide decomposition ; carbon‐supported copper catalysts
Source: Springer Online Journal Archives 1860-2000
Topics: Chemistry and Pharmacology
Notes: Abstract Copper supported on three different allotropic forms of carbon materials have been prepared and evaluated as catalysts for the N2O decomposition and reduction reactions. It was found that all the catalysts underwent severe deactivation during the N2O decomposition reaction due to the gasification of carbon substrates. This behavior was particularly evident when activated carbon was used as the support medium. The chemical identity of the active entity involved in the carbon gasification process is believed to consist of a mixture of Cu+ and Cu2+ species and, according to the well established mechanism, the reaction proceeds in such a manner so that the surface of the catalyst undergoes a redox cycle at the gas/solid carbon interface. The introduction of CO into the system was shown to result not only in an enhancement in the activity of the desired N2O decomposition reaction, but also served to inhibit the deleterious carbon gasification process. In addition, this procedure stabilized the copper particles in the metallic state, which is the active species responsible for the dissociation of N2O. Copper dispersed on a diamond substrate appeared to attain the highest activity for the N2O reduction reaction, a feature that is associated with the ability of the metal to undergo a wetting and spreading action on the support surface, possibly resulting in an epitaxial relationship between the two components.
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