| 1. |
- Ackelid, U, et al.
(author)
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Kinetics of ethylene oxidation on plane Pt/SiO2 catalysts in the viscous pressure regime: Evidence of support activity
- 1996
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In: Catalysis Letters. - 1011-372X. ; 39:1-2, s. 129-139
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Journal article (peer-reviewed)abstract
- C2H4 oxidation on plane Pt/SiO2 model catalysts with various Pt loadings was studied at T = 373-473 K and in the pressure ranges 10-6-102 Torr C2H4 and 0.3-1500 Torr O2 (1 Torr = 133.3 Pa). Mass spectrometry combined with spatially resolved gas sampling enabled kinetic data to be collected far into the viscous pressure regime. Reaction orders and activation energies were similar to those of a macroscopic Pt surface. However, under fuel-lean conditions the global reaction rate decreases faster than the decrease in metal area. On the other hand, the global rate was independent of Pt loading and metal surface area in fuel-rich gas mixtures. This is interpreted in terms of a spillover effect.
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| 2. |
- Andersson, Arne, et al.
(author)
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Ammoxidation of toluene over molybdenum oxides
- 1988
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In: Catalysis Letters. - 1011-372X. ; 1:11, s. 377-383
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Journal article (peer-reviewed)abstract
- The ammoxidation of toluene was studied both in presence and absence of gaseous oxygen over MoO3 and in situ prepared Mo4O11 (orth.) and MoO2. Irrespective of the partial pressure of oxygen, total reaction rates decrease in the following order: MoO3 > Mo4O11 > MoO2. The corresponding sequence for the selectivity towards formation of benzonitrile was found to depend on the partial pressure of oxygen. In two phase samples, no synergistic effects were observed for the formations of nitrile and carbon oxides. A comparison of rates for selective and nonselective products obtained in presence of gaseous oxygen with those obtained in its absence yield information as to whether the various products are formed at identical or different crystal faces. In the case of MoO3, nitrile and carbon oxides were found to be competitively formed at the same faces, while over MoO2 they are formed at different faces. Both options seem to prevail on
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| 3. |
- Arve, Kalle, et al.
(author)
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Did Chemisorption Become an Obsolete Method With Advent of Tem? Comparison of Mean Particle Size and Distribution of Silver on Alumina
- 2011
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In: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 141:5, s. 665-669
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Journal article (peer-reviewed)abstract
- Silver particle size and dispersion on a Ag/Al2O3 for HC-SCR were examined by means of chemisorption and TEM. Experimental results showed that determination of the accurate mean particle size (mps) is challenging and that the both applied methods have specific characteristics increasing the inaccuracy in the results which has to be taken into account in evaluation of catalytic activity. The results from TEM imaging were found to depend highly on the mode in which the surface was scanned (bright field versus dark field). Generally the point resolution was higher in dark field but the obtained mps did not increased along with the increasing silver loading. The main limitation with the O-2-chemisorption was related to the choice of the stoichiometric factor between the adsorbent and silver atoms. However, together these techniques support each other and help to give a more realistic picture of the mean silver particle size, distribution and indications of the oxidation states on the alumina support.
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| 4. |
- Auvray, Xavier, 1986, et al.
(author)
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Effect of enhanced support acidity on the sulfate storage and the activity of Pt/γ-Al2O3 for no oxidation and propylene oxidation
- 2014
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In: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 144:1, s. 22-31
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Journal article (peer-reviewed)abstract
- NO oxidation and propylene oxidation were studied on standard and acidity-enhanced Pt/Al 2 O 3 catalyst. Deactivation by platinum oxide formation was suppressed by the presence of chlorine and sulfates. After a long SO 2 exposure, the activity of modified catalysts was higher than the standard catalyst. The aged chlorinated sample showed the best propylene oxidation activity while the sulfated one exhibited the best NO conversion. © 2013 Springer Science+Business Media New York.
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| 5. |
- Berggrund, Malin, 1966, et al.
(author)
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Influence of Synthesis Conditions for ZSM-5 on the Hydrothermal Stability of Cu-ZSM-5
- 2009
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In: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 130:1-2, s. 79-85
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Journal article (peer-reviewed)abstract
- The influence of syntheses parameters of zeolite ZSM-5 on the lean NO (x) reduction activity and hydrothermal stability of Cu-ZSM-5 has been investigated. The hydrothermal stability of Cu-ZSM-5 was found to depend on the aluminium source used and on the presence of Ca(OH)(2) in the synthesis mixture for ZSM-5.
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| 6. |
- Brandin, Jan, 1958-, et al.
(author)
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Deactivation and Characterization of SCR Catalysts Used in Municipal Waste Incineration Applications
- 2018
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In: Catalysis Letters. - : Springer. - 1011-372X .- 1572-879X. ; 148:1, s. 312-327
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Journal article (peer-reviewed)abstract
- Catalysts used for selective catalytic reduction were deactivated for various times in a slipstream from a municipal solid waste incineration plant and then characterized. The activity for NO reduction with NH3 was measured. The Brunauer–Emmett–Teller surface areas were determined by N2 adsorption from which the pore size distributions in the mesopore region were obtained. Micropore areas and volumes were also obtained. The composition of fresh and deactivated catalysts as well as fly ash was determined by atomic absorption spectroscopy and scanning electron microscopy with energy dispersive X-ray analysis. The changes in surface area (8% decrease in BET surface area over 2311 h) and pore structure were small, while the change in activity was considerable. The apparent pre-exponential factor was 1.63 × 105 (1/min) in the most deactivated catalyst, compared to 2.65 × 106 (1/min) in the fresh catalyst, i.e. a reduction of 94%. The apparent activation energy for the fresh catalyst was 40 kJ/mol, decreasing to 27 kJ/mol with increasing deactivation. Characterization showed that catalytic poisoning is mainly due to decreased acidity of the catalyst caused due to increasing amounts of Na and K.
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| 7. |
- Bratlie, Kaitlin M., et al.
(author)
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Compensation effect of benzene hydrogenation on Pt(111) and Pt(100) analyzed by the selective energy transfer model
- 2008
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In: Catalysis Letters. - : Springer Science and Business Media LLC. - 1011-372X .- 1572-879X. ; 121:3-4, s. 173-178
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Journal article (peer-reviewed)abstract
- Kinetic measurements at low temperatures (310-360 K) using gas chromatography (GC) for benzene hydrogenation on Pt(100) and Pt(111) single crystal surfaces have been carried out at Torr pressures. These kinetic measurements demonstrated a linear compensation effect for the production of cyclohexane. A detailed application of the model of selective energy transfer to the experimentally obtained results yields the vibrational frequency of the adsorbate leading to reaction. This frequency is attributed to ring distortion modes. The vibrational frequency of the heat bath, or catalyst, is ascribed to a Pt-H mode. An approximate heat of adsorption of the reacting molecule is also calculated from the model.
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| 8. |
- Carlsson, Per-Anders, 1972, et al.
(author)
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Methane oxidation over Pt/Al2O3 and Pd/Al2O3 catalysts under transient conditions
- 2007
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In: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 115:1-2, s. 1-7
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Journal article (peer-reviewed)abstract
- We communicate experimental results for the oxidation of methane by oxygen over alumina supported Pd and Pt monolith catalysts under transient conditions. Temperature programmed reaction (TPReaction) and reactant pulse-response (PR) experiments have been performed, using a continuous gas-flow reactor equipped with a downstream mass spectrometer for gas phase analysis. Special attention was paid to the influence of gas composition changes, i.e., O 2 and H 2 pulsing, respectively, on the methane conversion. For Pt/Al 2 O 3 oxygen pulsing can significantly increase the methane conversion which can be even further improved by pulsing hydrogen instead. Such transient effects are not observed for the Pd/Al 2 O 3 catalyst for which instead constantly lean conditions is beneficial. Our results suggest that under lean conditions Pd and Pt crystallites may undergo bulk- and partial (surface oxide formation) oxidation, respectively, which for Pd results in more active surfaces, while for Pt the activity is reduced. The latter seems to connect to a lowering of the ability to dissociate methane. © 2007 Springer Science+Business Media, LLC.
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| 9. |
- Dahl, Leif, et al.
(author)
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Catalytic behavior and characterization of (CuO)1-z(La2O3)z/2 based catalysts deposited on γ-Al2O3 and prepared in situ with 0.0≤z≤1.00 with and without addition of Pd
- 1996
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In: Catalysis Letters. - 1572-879X .- 1011-372X. ; 37:1-2, s. 69-77
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Journal article (peer-reviewed)abstract
- (CuO)(1-z)(La2O3)(z/2) based catalysts with 0.0 less than or equal to z less than or equal to 1.0 supported on gamma-Al2O3 have been prepared in situ and the phases formed have been identified by XRD, SEM and TEM/EDS studies. The catalyst with z = 0.5 exhibited the best catalytic activity for oxidation of CO (T-50 = 295 and 390 degrees C with degrees of conversions of 93 and 92% at 450 degrees C under rich and lean conditions, respectively) and C3H6 (291 and 414 degrees C; 93 and 83%) and reduction of NO (405 degrees C; 60 and 0%). This catalyst contained appreciable amounts of the perovskite phase LaAl1-xCuxO3 and the enhanced catalytic properties are ascribed to the presence of this phase. Addition of Pd to this catalyst implied that the degree of conversion of NO increased and that the light-off temperatures for all involved gas species decreased. Ageing experiments revealed that LaAl1-xCuxO3 decomposed and that Cu containing Pd particles were formed during this procedure which in turn deteriorated the catalytic properties of the catalyst.
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| 10. |
- Erkfeldt, Sara U, 1974, et al.
(author)
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Promoting Effect of Triglyme on Lean NOx Reduction Over Ag/Al2O3
- 2012
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In: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 142:2, s. 183-189
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Journal article (peer-reviewed)abstract
- The highly oxygenated hydrocarbon triethylene glycol dimethyl ether or triglyme (CH3O-(C2H4O-)(3)CH3) was found to efficiently reduce NOx under lean conditions over Ag/Al2O3, but gave a low NOx conversion over Cu-ZSM-5. Furthermore, triglyme showed an extraordinary promoting effect when added together with propene as reducing agent for NOx over Ag/Al2O3 at low temperature. This is most likely due to that triglyme promotes the activation of propene.
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