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  • Electronic Resource  (8)
  • Ammonia synthesis  (3)
  • silver  (3)
  • N2 TPD  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Application of Ru exchanged zeolite-Y in ammonia synthesis (1992)
    Springer
    Catalysis letters 14 (1992), S. 339-348 
    Details
    ISSN: 1572-879X
    Keywords: Ammonia synthesis ; Ru-zeolite ; metal clusters ; conversion measurements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Na-Y zeolite was cation exchanged with Ru(NH3)6Cl3 yielding at 25% exchange level a light-purple solid which was active in ammonia synthesis at atmospheric pressure. Pulse conversion experiments show that the catalyst stores nitrogen as it was observed with the conventional iron catalyst. At 810 K the conversion reached about 20% of the maximum conversion of the iron catalyst. The catalyst deactivated reversibly within 30 h due to agglomeration. The active species in the catalyst is most likely a cluster-like Ru metal particle prevented from sintering under the reducing conditions of catalysis by the zeolite framework.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00769672
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  • 2
    Electronic Resource
    Electronic Resource
    On the nature of the active state of silver during catalytic oxidation of methanol (1993)
    Springer
    Catalysis letters 22 (1993), S. 215-225 
    Details
    ISSN: 1572-879X
    Keywords: Ion-scattering spectroscopy (ISS) ; methanol oxidation ; oxygen ; Raman spectroscopy ; reflection electron microscopy (REM) ; silver ; X-ray photoelectron spectroscopy (XPS)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Under the applied high reaction temperatures (∼900 K) the Ag surface is restructured and a tightly held oxygen species is formed on the surface (Oγ) apart from O atoms dissolved in the bulk (Oβ). Methanol oxidation to formaldehyde proceeds through this Oγ species as demonstrated by application of a variety of spectroscopic techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00810368
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  • 3
    Electronic Resource
    Electronic Resource
    The dissociative adsorption of N2 on a multiply promoted iron catalyst used for ammonia synthesis: a temperature-programmed desorption study (1994)
    Springer
    Catalysis letters 24 (1994), S. 317-331 
    Details
    ISSN: 1572-879X
    Keywords: Nitrogen adsorption ; N2 TPD ; iron-based catalyst ; ammonia synthesis ; microkinetic analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The temperature-programmed desorption (TPD) of N2 from a multiply promoted iron catalyst used for ammonia synthesis has been studied in a microreactor system at atmospheric pressure. From TPD experiments with various heating rates a preexponential factorA = 2 × 109 molecules/site s and an activation energyE = 146 kJ/mol was derived assuming second-order desorption. The observed dependence of the TPD peak shapes on the heating rates indicated the influence of readsorption of N2 in agreement with the results obtained for various initial coverages. Simulating the N2 TPD curves using the model by Stoltze and Nørskov revealed that the calculated TPD curves were not influenced by the molecular precursor to desorption. However, the calculated rate of readsorption was found to be overestimated at high coverage compared with the experimental results. A coverage-dependent net activation energy for dissociative chemisorption (E*) was introduced as the simplest assumption rendering the dissociative chemisorption of N2 activated at high coverage. The best fit of the experimental data yieldedE* = (−15+30θ) kJ/mol using only a single type of atomic nitrogen species. These findings are in satisfactory agreement with the parameters underlying the Stoltze-Nørskov model for the kinetics of ammonia synthesis as well as with the data reported for Fe(111) single crystal surfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811804
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  • 4
    Electronic Resource
    Electronic Resource
    Oxidative coupling of methane on silver catalysts (1995)
    Springer
    Catalysis letters 32 (1995), S. 185-194 
    Details
    ISSN: 1572-879X
    Keywords: methane ; silver ; oxidative coupling ; C2 selectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bulk silver catalysts were found to be active for the oxidative coupling of methane to ethane and ethylene if operated under oxygen-limited conditions at atmospheric pressure and at temperatures above 1020 K. The addition of small amounts of sodium phosphate as promoter increases markedly the C2 selectivity (to values above 90%) and yield (〉10%) by efficient suppression of reaction steps leading to total oxidation. Further improvement of the yields might be achieved by more appropriate reactor design.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806113
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of water on the formation of strongly bound oxygen on silver surfaces (1995)
    Springer
    Catalysis letters 32 (1995), S. 171-183 
    Details
    ISSN: 1572-879X
    Keywords: oxygen ; partial oxidation ; reconstruction ; reflection electron microscopy ; Raman spectroscopy ; silver ; water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Interaction of water with an oxygenated Ag(111) surface leads to an enhancement of the surface restructuring and an activated formation of hydroxyl groups (OH) located stably on the surface and incorporated in the subsurface region, as evidenced by means of reflection electron microscopy (REM) and in situ Raman spectroscopy. Dehydroxylation of OHads at elevated temperatures releases the strongly bound oxygen species labelled Oγ at the surface, and offers an alternative to the energetically less favorable pathway for the direct formation of the Oγ species from molecular oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806112
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  • 6
    Electronic Resource
    Electronic Resource
    The temperature-programmed desorption of N2 from a Ru/MgO catalyst used for ammonia synthesis (1996)
    Springer
    Catalysis letters 36 (1996), S. 229-235 
    Details
    ISSN: 1572-879X
    Keywords: N2 TPD ; N2 adsorption ; Ru ; MgO ; NH3 synthesis ; microkinetic analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The temperature-programmed desorption (TPD) of N2 from a Ru/MgO catalyst used for ammonia synthesis was studied in a microreactor flow system operating at atmospheric pressure. Saturation with chemisorbed atomic nitrogen (N-*) was achieved by exposure to N2 at 573 K for 14 h and subsequent cooling in N2 to room temperature. With a heating rate of 5 K/min in He, a narrow and fairly symmetric N2 TPD peak at about 640 K results. From experiments with varying heating rates a preexponential factor Ades = 1.5×1010 molecules/(site s) and an activation energy Edes = 158 kJ/mol was derived assuming secondorder desorption. This rate constant of desorption is in good agreement with results obtained with a Ru(0001) single crystal surface in ultra-high vacuum (UHV). The rate of dissociative chemisorption was determined by varying the N2 exposure conditions. Determination of the coverage of N-* was based on the integration of the subsequently recorded N2 TPD traces yielding Aads = 2×10−6 (Pa s)−1 and Eads = 27 kJ/mol. The corresponding sticking coefficient of about 10−14 at 300 K is in agreement with the inertness of Ru(0001) in UHV towards dissociative chemisorption of N2. However, if the whole catalytic surface were in this state, then the resulting rate of N2 dissociation would be several orders of magnitude lower than the observed rate of NH3 formation. Hence only a small fraction of the total Rumetal surface area of Ru/MgO seems to be highly active dominating the rate of ammonia formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807624
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  • 7
    Electronic Resource
    Electronic Resource
    Microstructure of the activated industrial ammonia synthesis catalyst (1991)
    Springer
    Catalysis letters 11 (1991), S. 19-31 
    Details
    ISSN: 1572-879X
    Keywords: Ammonia synthesis ; iron catalyst ; surface characterization ; promoter effects ; nitrides ; ion scattering spectroscopy ; XPS ; HRTEM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Industrial doubly-promoted iron catalysts and model systems of singly-promoted K- and Al-iron catalysts were characterised by their catalytic performance at 1 bar pressure. The relevance of bulk nitrogen for catalytic performance is shown. The catalysts were also activated in an in-situ reaction chamber of a He-ion scattering spectrometer (ISS) and their top atomic layer elemental composition was determined after they had reached similar performance as in the microreactor tests. The bulk microstructure of these samples was investigated by high resolution transmission electron microscopy (TEM) and microdiffraction. All evidence indicates that small highly crystalline α-Fe platelets act as active phase. Their surfaces are covered to a large extent by promotor compounds which are partly present as poorly crystalline aggregates with iron oxide leaving only a small fraction of elemental iron directly exposed to the gas phase. The intimate contact between iron crystals and promoters particles prevents recrystallisation and is the key to the understanding of the structural stability of the catalyst system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00866897
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  • 8
    Electronic Resource
    Electronic Resource
    Ruthenium supported on zeolite A: preparation and characterisation of a stable catalyst for ammonia synthesis (1994)
    Springer
    Catalysis letters 25 (1994), S. 61-74 
    Details
    ISSN: 1572-879X
    Keywords: Ammonia synthesis ; supported ruthenium catalyst ; dispersed ruthenium ; instationary kinetics ; lifetime effects ; ruthenium oxidation ; surface analysis ; XPS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Reaction of Ru(NH3)6Cl3 with Na-A and K-A zeolites yielded oligomeric amino-oxo-complexes supported on the zeolite. Controlled thermal activation under hydrogen converted the precursor in a two-step reaction into an active catalyst with good long-term stability and resistance against small doses of oxygen poison. Several nanometers sized Ru metal particles are chemically bonded to the zeolite surface which provides in the K form an alkali promoter at the metal-zeolite interface. Extensive oxidation breaks the metal-support anchoring and re-reduction produces Ru metal particles sintering rapidly into large metal crystals with only small residual catalytic activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00815416
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