| 1. |
- Acke, Filip, 1968, et al.
(författare)
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Comparison between ammonia and propene as the reducing agent in the selective catalytic reduction of NO under lean conditions over Pt black
- 1999
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 20:2, s. 133-144
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic activity of Pt black towards the reduction of NO under lean conditions is examined. Ammonia and propene are tested as reducing agents. A scrambling between nitrogens is observed in the formation of N2 and N2O for NH3. For C3H6, a reduction of NO to mainly N2O is found. A minor formation of N2 is only observed for high C3H6 concentrations. The role of NO2 as an intermediate in the reduction of NO is examined by using a feed gas mixture containing NO2, as well as by studying the catalytic activity of Pt black towards the NO-O2 and NO2-O2 reactions. No effect is observed in the maximum NOx conversion for C3H6 whereas for NH3 a decreased activity is found. The presented results are put in perspective of the reaction mechanisms proposed in the literature.
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| 2. |
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| 3. |
- Acke, Filip, 1968, et al.
(författare)
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Zeolite supported Pt catalysts for reduction of NO under oxygen excess: a comparison of C3H6, HNCO and NH3 as reducing agents
- 1999
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 20:3, s. 235-242
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the zeolite SiO2/Al2O3 ratio of ZSM-5 supported Pt catalysts on the reduction of NO under oxygen excess has been investigated. The activity and selectivity of three reducing agents were compared, i.e. C3H6, HNCO and NH3. The maximum NO reduction with both C3H6 and HNCO as the reducing agent was affected by the SiO2/Al2O3 ratio of the support. Although no effect was observed on the maximum NO reduction for NH3, the yields of Nz and N2O were affected. The results are put in perspective of reaction mechanisms proposed in the literature.
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| 4. |
- Engström, Per, et al.
(författare)
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Sulphur dioxide interaction with NOx storage catalysts
- 1999
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 22:4, s. L241-L248
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Tidskriftsartikel (refereegranskat)abstract
- The effect of SO2 on the NOx storage capacity and oxidation and reduction activities of a model Pt/Rh/BaO/Al2O3 NOx storage catalyst was investigated. Addition of 2.5, 7.5 or 25 vol. ppm SO2 to a synthetic lean exhaust gas caused deactivation of the NOx storage function, the oxidation activity and the reduction activity of the catalyst. The degree of deactivation of the NOx storage capacity was found to be proportional to the total SO2 dose that the catalyst had been exposed to. SO2 was found to be accumulated in the catalyst as sulphate.
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| 5. |
- Lin, Pei-yan, et al.
(författare)
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Catalytic purification of car exhausts over cobalt- and copper-based metal oxides promoted with platinum and rhodium
- 1995
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 6:3, s. 237-319
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Tidskriftsartikel (refereegranskat)abstract
- 25 Alumina-and silica-supported oxide-based catalysts were prepared, with the overall metal composition La(0.45)Sr(0.15)Ce(0.35)Zr(0.05)M(1.0) (M=Co or Cu) and promoted with 0-0.5 mg Pt-Rh per gram catalyst. The catalysts were evaluated with respect to light-off temperatures and redox characteristics, using NO/CO/C3H6/O2/N2 gas mixtures to simulate car exhaust. The activities for complete oxidation of propene and carbon monoxide increased with increasing content of metal oxides and noble metals. The catalysts were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) combined with energy-dispersive spectroscopy (EDS) analysis, temperature-programmed reduction (TPR), and specific surface area measurements (BET). SEM/TEM/XRD revealed that the alumina-supported catalysts contained well dispersed oxides of the added elements, whereas the silica-supported catalysts contained significantly larger particles of the copper or cobalt oxides, The TPR peak for reduction of cobalt oxide shifted toward lower temperatures with increasing content of Pt-Rh, indicating hydrogen spill-over from the noble metals to the cobalt oxide. The catalytic activity of the Co-based oxides supported on alumina and promoted with 0.49 mg Pt-Rh per gram catalysts was comparable to the activity of a commercial three-way catalyst (TWC), containing more than 4 times as much Pt-Rh.
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| 6. |
- Odenbrand, Ingemar, et al.
(författare)
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Lean NOx reduction in real diesel exhaust with copper and platinum titania based monolithic catalysts
- 1999
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373. ; 23:1, s. 37-44
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Tidskriftsartikel (refereegranskat)abstract
- A study on the catalytic behaviour of a copper and a platinum titania based monolithic catalyst in the reduction of nitrogen oxides with hydrocarbons in real diesel conditions was carried out. A Volvo TD 7.31 engine was used as gas source, and diesel fuel was the reductant. In these conditions, both catalysts were active in the reduction reaction. The influence of various operating parameters on the catalytic activity, as engine speed and reductant concentration in the gas has studied. Other aspects were also studied as selectivity of reduction to nitrous oxide, nitrogen monoxide oxidation into nitrogen dioxide, and generation of carbon monoxide. The selectivity in the reduction of NO to N2O with the diesel exhaust was relatively low with both titania supported systems. Opposite behaviours of both catalysts in NO to NO2 oxidation were observed, indicating two different mechanisms for this reaction. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 7. |
- Skoglundh, Magnus, 1965, et al.
(författare)
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Cobalt-promoted palladium as three-way catalyst
- 1996
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 7:3-4, s. 299-319
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Tidskriftsartikel (refereegranskat)abstract
- Fifteen catalysts were prepared by intermittently impregnating alumina washcoats with water solutions containing La3+, Co2+ and PdCl42- ions/complex and calcining them at 550-820 degrees C. The catalysts were evaluated with respect to light-off performance, at stationary and transient feed gas stoichiometry, respectively, and redox characteristics, using NO/CO/C3H6/O-2/N-2 gas mixtures to simulate car exhaust. Alumina supported Pd exhibited three-way activity, i.e., simultaneous oxidation of CO and C3H6 and reduction of NO in a narrow interval around stoichiometric composition of the feed gas. Compared to Pd alone, addition of La or Co caused a widening of the interval under net reducing conditions. Addition of Co to Pd caused a significant increase in the activities for oxidation of CO and C3H6 under stoichiometric conditions. The conversions of CO and C3H6 started at about 100 degrees lower temperatures over Co-promoted Pd compared to unpromoted Pd. A marked increase in the activity for the reduction of NO at transient conditions was observed over Co-promoted Pd compared to unpromoted Pd. The catalysts were characterized by X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy combined with energy-dispersive spectroscopy analysis, X-ray photoelectron spectroscopy (XPS), and specific surface area measurements. Only Co2+ could be detected by XPS in the surface layers of the Co-containing sample. A significant part of the cobalt is present in forms which can be oxidized and reduced under synthetic car exhaust conditions. These oxidizable/reducible cobalt sites are predominantly active for oxidation of CO and C3H6, hence promoting the reduction of NO over Pd by initiating these exothermic reactions in the catalyst.
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| 8. |
- Törncrona, Anders, 1967, et al.
(författare)
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Low temperature catalytic activity of cobalt oxide and ceria promoted Pt and Pd: -Influence of pretreatment and gas composition
- 1997
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 14:1-2, s. 131-146
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Tidskriftsartikel (refereegranskat)abstract
- The influence of pretreatment, gas composition and metal (Ce or Co) oxide promotion on the low-temperature CO and C3H6 oxidation activity over alumina-supported Pt and Pd has been studied. The monolith catalysts have either been preoxidised in O2/N2 Or prereduced in H2/N2 prior to evaluation with respect to light-off performance, using either net oxidising or net reducing CO/C3H6/O2/N2 gas mixtures. Compared with unpromoted Pt, promotion with preoxidised ceria or cobalt oxide enhances the low-temperature activity significantly and lowers the light-off temperatures by about 60-70 degrees C for both CO and C3H6. Prereduction of a cobalt-oxide catalyst (without precious metals) gives a dramatically improved performance compared with a preoxidised catalyst in terms of light-off and overall conversion. Prereduction of metal oxide promoted Pt and Pd can shift the light-off temperatures for CO and C3H6 by up to 100 degrees C toward lower temperatures compared with preoxidised samples. When using gas mixtures containing both CO and C3H6, the conversion of CO always starts at lower temperatures than the conversion of C3H6 The catalysts have been characterised by temperature-programmed desorption (TPD) of carbon monoxide, X-ray photoelectron spectroscopy (XPS), and specific surface area measurements (BET). The reduced cobalt containing samples adsorb large amounts of CO. The high activity over the catalysts containing prereduced cobalt oxide is suggested to be due to the presence of reduced cobalt-oxide sites on the surface of those samples.
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| 9. |
- Ganemi, B., et al.
(författare)
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Conversion and in situ FTIR studies of direct NO decomposition over Cu-ZSM5
- 1998
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Ingår i: Applied Catalysis B. - 0926-3373 .- 1873-3883. ; 17:4, s. 293-311
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Tidskriftsartikel (refereegranskat)abstract
- Copper ion-exchanged zeolites ZSMS with SiO2:Al2O3 molar ratios 33 and 53 have been subjected to activity tests for direct decomposition of NO (2000 ppm, GHSV 560-5400 h(-1)). In situ infrared measurements were used to follow the reaction and surface and gas phase compositions. IR studies were also done in excess oxygen with rapid NO2 formation in the gas phase. A high level of overexchange of copper in the zeolite in combination with a low concentration of acid sites, concurrent with a high SiO2:Al2O3 ratio, enhances the conversion of NO. A vibrational band at 1631 cm(-1) is observed below the light-off temperature and interpreted as a bridged nitrate group bound to Cu2+-O-Cu2+ dimers. This band disappears above the light-off temperature but the intensity below this temperature correlates with the catalytic activity. We interpret that these bridge bound nitrate groups act as siteblockers on the active sites for NO conversion and that a tentative reaction intermediate, N2O3, also binds in a bridge configuration to the same Cu2+-O-Cu2+ dimers.A second nitrate group with unidentate coordination and vibrational bands at 1598/1575 cm(-1) probes isolated copper ions.A third infrared band at 2130 cm(-1) confirms previous observations of NO2+-ions bound to the zeolite. We conclude that these species are coordinated to deprotonated and negatively charged sites on the zeolite and that these sites for NO2+ adsorption are blocked by Cu2+ ion-exchange. The 2130 cm(-1) species appear to have no role in direct NO decomposition but the adsorption sites are crucial for the stability of the zeolite and intimately related to ion mobility in the lattice.Prolonged immersion of the zeolite in dilute solutions of copper ions improves the catalyst performance by copper hydroxylation leading to enhanced formation of the above dimers.A high SiO2:Al2O3 ratio leads to more stable catalysts, particularly in combination with a modest overexchange of copper ions. Excessive amounts of copper escalates the deactivation of the Cu-ZSM5 catalyst through the migration and sintering of cupric oxide crystallites.
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| 10. |
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