| 1. |
- Acke, Filip, 1968, et al.
(författare)
-
Comparison between ammonia and propene as the reducing agent in the selective catalytic reduction of NO under lean conditions over Pt black
- 1999
-
Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 20:2, s. 133-144
-
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.
|
|
| 2. |
|
|
| 3. |
- Acke, Filip, 1968, et al.
(författare)
-
Zeolite supported Pt catalysts for reduction of NO under oxygen excess: a comparison of C3H6, HNCO and NH3 as reducing agents
- 1999
-
Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 20:3, s. 235-242
-
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.
|
|
| 4. |
- Amberntsson, Annika, 1974, et al.
(författare)
-
Influence of platinum and rhodium composition on the NOx storage and sulphur tolerance of a barium based NOx storage catalyst
- 2003
-
Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 46:3, s. 429-439
-
Tidskriftsartikel (refereegranskat)abstract
- In the present work the influence of the type of noble metals present in barium oxide based NOx storage catalysts was investigated, regarding the NOx storage performance, NO oxidation, NO reduction, sulphur deactivation and sulphur regenerability. Monolith samples with combinations of platinum and rhodium, were prepared, tested in a flow-reactor, and characterised by XPS measurements. The flow-reactor experiments simulated NOx storage and reduction cycles at 400 degrees C in synthetic gas mixtures with oxygen, propene and nitric oxide. For the sulphur deactivation and regenerability investigations 25 ppm (v/v) SO2 was added to the feed gas stream. From the experiments, it was concluded that a combination of platinum and rhodium is required to achieve good NOx storage and reduction performance. The NOx storage capacity was, however, found higher for catalysts containing only platinum compared to catalysts including rhodium. When exposed to SO2 the NOx storage capacity also seemed to deactivate faster for the samples containing rhodium than for samples with platinum as the sole noble metal. Additionally, it was observed that platinum gives high NO oxidation activity during the lean periods both with and without SO2 present in the gas feed. During the rich periods, rhodium showed high activity for NO reduction in sulphur free gas feed as well as in the presence of SO2. Finally, the results implied that to provide good sulphur regeneration ability of the NOx storage catalyst, a combination of platinum and rhodium is necessary.
|
|
| 5. |
- Engström, Per, et al.
(författare)
-
Sulphur dioxide interaction with NOx storage catalysts
- 1999
-
Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 22:4, s. L241-L248
-
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.
|
|
| 6. |
- Härelind Ingelsten, Hanna, 1973, et al.
(författare)
-
Influence of the Support Acidity of Pt/Aluminum-Silicate Catalysts on the Continuous Reduction of NO under Lean Conditions
- 2003
-
Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 41:3, s. 287-300
-
Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the influence of the support acidity on the continuous reduction of nitric oxide by hydrocarbons over supported Pt catalysts under lean conditions. The support materials used were alumina, silica and co-precipitated aluminum-silicates. Activity studies of NO reduction with either propene or propane as the reducing agent, CO chemisorption, CO oxidation, isopropylamine temperature programmed desorption (TPD) and ammonia TPD experiments have been performed. The isopropylamine TPD experiments indicated the presence of Bronsted acid sites in the samples that contained alumina. The activity for NO reduction and the selectivity for N-2 formation with propene as the reducing agent showed no pronounced differences between the samples studied. For propane, on the other hand, expressed differences in NO reduction activity between the samples were observed. The activation of propane and consequently the reduction of NO, seemed to be promoted by the presence of acidic sites on the surface of the support. The selectivity towards N2 formation seemed to be strongly connected to the amount of Bronsted acid sites present in the samples.
|
|
| 7. |
- Lin, Pei-yan, et al.
(författare)
-
Catalytic purification of car exhausts over cobalt- and copper-based metal oxides promoted with platinum and rhodium
- 1995
-
Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 6:3, s. 237-319
-
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.
|
|
| 8. |
- Moradi, Farokhbag, et al.
(författare)
-
Deactivation of oxidation and SCR catalysts used in flue gas cleaning by exposure to aerosols of high- and low melting point salts, potassium salts and zinc chloride
- 2003
-
Ingår i: Applied Catalysis B: Environmental. - : Elsevier. - 0926-3373 .- 1873-3883. ; 46:1, s. 65-76
-
Tidskriftsartikel (refereegranskat)abstract
- For the purpose of this deactivation study, Pt- and vanadia supported catalysts were used. The catalysts have been exposed to aerosol particles of inorganic salts, with high- or low melting points. The average diameter of the generated salt particle was kept constant at around 70 nm. The aerosol particle penetration depth for the samples exposed to potassium salt, was 1 μm as measured by scanning electron microscopy (SEM). The corresponding depth for zinc chloride salt (ZnCl2) was 5 μm. In order to validate the dependency of the catalytic decay rate to exposure temperature, Pt/wire-mesh catalyst was treated with potassium chloride at two temperatures, namely 300 and 500 °C. Pt/supported catalyst was also treated with ZnCl2 salt at 190 and 300 °C. The extent of decay was tested in the oxidation of CO for particle treated Pt/wire-mesh samples. The degree of the deactivation for the aerosol particle deactivated vanadia supported catalysts were also examined in the reduction of NOx. When the Pt/wire-mesh catalyst have been exposed to the poisons aerosol particles at higher temperature lead to the strongest deactivation in the CO oxidation. The Pt-supported catalysts that were treated with aerosol particles from potassium carbonate and potassium sulphate revealed a minor deactivation in the CO oxidation reaction. No significant deactivation was observed for the salt treated vanadia supported monolith samples used in selective catalytic reduction (SCR). A slight pronunced deactivation effect appeared when the vanadia supported wire-mesh catalysts were salt treated. Generally, the obtained results in this study do not indicate any correlation between the salt melting point and the degree of catalytic decay. The obtained results indicate that the exposure temperature during the deactivation procedure is the most critical parameter. Also, the higher the exposing temperature the stronger deactivated sample is produced.
|
|
| 9. |
- Salasc, Sophie, et al.
(författare)
-
A comparison between Pt and Pd in NOx storage catalysts
- 2002
-
Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 36:2, s. 145-160
-
Tidskriftsartikel (refereegranskat)abstract
- The importance of Pt and Pd in noble metal-barium oxide type NOx storage catalysts was investigated. Model Pt/BaO/Al2O3 and Pd/BaO/Al2O3 catalysts were prepared and evaluated with respect to NOx storage capacity, activity towards NO reduction under lean conditions and NO oxidation capacity using synthetic lean burn exhausts containing NO, O2, C3H6 and N2. The study was carried out by performing static and transient flow reactor experiments and temperature-programmed desorptionstudies. At 300 degrees C, the Pd/BaO/Al2O3 sample shows a higher NOx storage capacity than Pt/BaO/Al2O3, i.e. more NOx is stored during the lean periods and almost all NOx is released and reduced during the subsequent rich periods. At this temperature(300 degrees C), the NO reduction is not complete during the rich phase for the Pt-based catalyst suggesting poisoning of Pt-sites by adsorbed species. At 400 degrees C, Pt/BaO/Al2O3 stores slightly more NOx than its Pd-based counterpart. XPS measurements on pre-treated catalysts, show some changes in oxidation state for Pd between the rich and lean phases. The oxidation of NO is much more limited on Pd based samples compared to Pt containing catalysts. The importance of NO2 as an intermediate in the storage of NOx as nitrate under lean conditions is confirmed in this study.
|
|
| 10. |
- Skoglundh, Magnus, 1965, et al.
(författare)
-
Cobalt-promoted palladium as three-way catalyst
- 1996
-
Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 7:3-4, s. 299-319
-
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.
|
|
