| 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. |
- Amberntsson, Annika, 1974, et al.
(författare)
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Influence of platinum and rhodium composition on the NOx storage and sulphur tolerance of a barium based NOx storage catalyst
- 2003
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 46:3, s. 429-439
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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.
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| 5. |
- 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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| 6. |
- Hinz, A, et al.
(författare)
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Platinum on alumina, titania, and magnesia supports for the combustion of methanol in a waste gas with trace amount of ammonia
- 2001
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373. ; 34:2, s. 161-178
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Tidskriftsartikel (refereegranskat)abstract
- Pt (0.1 wt.%) on Al2O3, TiO2, and MgO supports were used for the low temperature combustion of methanol in both the absence and the presence of ammonia. Without NH3 in the gas the performance for the complete combustion decreases in the order Pt/MgO greater than or equal to Pt/TiO2 much greater than Pt/Al2O3 comparing a fixed amount of Pt surface area. In the presence of ammonia strong deactivation of Pt/Al2O3 and Pt/TiO2 is observed, whilst almost no deactivation of Pt/MgO occurs. The results are explained considering CO chemisorption and XPS measurements as well as the TPD profiles generated by adsorbed ammonia and methanol. A comparison of the TPD profiles of the N-2 which is formed from adsorbed ammonia on supported Pt and the support, respectively, reveals that Pt on Al2O3 and TiO2 interacts with the support surface, possibly through Pt-O-support bonding. The inference is supported by the XPS measurements showing that the Pt on Al2O3 and TiO2, as opposed to that on MgO, is slightly positively charged, making the interaction between ammonia and Pt stronger. Additional insight into the deactivation cause is obtained from TPD experiments with adsorbed methanol. These experiments reveal that on both Pt/Al2O3 and Pt/TiO2 there is competition between methanol and ammonia for adsorption sites, which is not the case on Pt/MgO. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 7. |
- Härelind Ingelsten, Hanna, 1973, et al.
(författare)
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Influence of the Support Acidity of Pt/Aluminum-Silicate Catalysts on the Continuous Reduction of NO under Lean Conditions
- 2003
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 41:3, s. 287-300
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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.
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| 8. |
- Khodayari, R, et al.
(författare)
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Regeneration of commercial SCR catalysts by washing and sulphation: effect of sulphate groups on the activity
- 2001
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373. ; 33:4, s. 277-291
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Tidskriftsartikel (refereegranskat)abstract
- The use of bio-fuels is becoming more important because of the environmental benefits associated with these fuels. Deactivation of SCR catalysts applied in bio-fuel plants is a major problem due to the high potassium content of bio-fuels and therefore, great potential lies in finding regeneration processes that can be used commercially. Exposing the catalyst surface to sulphate groups generated by SO2 or H2SO4 is a promising way to rejuvenate the initial activity of the catalyst. The chemical stability of the sulphate groups was investigated by the interaction of the SCR reactant gases with the sulphate-promoted catalysts. Sulphate ions deposited on the surface of the TiO2/V2O5/WO3 were thermally stable at 420 degreesC. The introduced sulphate groups were chemically unstable when the catalyst was treated with the SCR reactants at 400 degreesC, but were chemically stable when the catalyst was exposed for the SCR reactants at 350 degreesC. Sulphation after water treatment provided more chemically stable surface sulphate groups at 400 degreesC. The presence of sulphate groups enhanced the number and the strength of the surface acid sites. The amount of ammonia bound to the Bronsted acid sites decreased with the potassium content of the catalyst while the amount of ammonia adsorbed on the Lewis acid sites was almost unaffected. Since potassium both retarded the redox potential of the surface vanadia species and decreased the amount of ammonia bound to the Bronsted acid sites, it is important to wash the strongly deactivated catalyst before sulphation. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 9. |
- Khodayari, R, et al.
(författare)
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Regeneration of commercial TiO2-V2O5-WO3SCR catalysts used in bio fuel plants
- 2001
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373. ; 30:1-2, s. 87-99
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Tidskriftsartikel (refereegranskat)abstract
- Deactivation of SCR catalysts applied in bio fuel plants is a major problem due to higher amounts of potassium in bio fuel compared to other fuels. Regeneration of deactivated catalysts seems to be a promising way for minimising the total cost of bio fuel plants and great potential lies in finding regeneration processes that can be used commercially. The first applied regeneration method was washing of two different commercially aged catalysts in different aqueous solutions. The other method was washing with water followed by sulphation at different temperatures. Sulphation with SO2 resulted in higher activation without affecting the amount of potassium accumulated on the surface indicating the role of surface sulphate groups. Since potassium both decreases the catalytic activity for NO-reduction and retards the redox potential of the surface vanadium species during the sulphation procedure, it is necessary to wash the heavily deactivated catalyst before sulphation. Washing with water or diluted sulphuric acid could not restore the vanadium groups to the initial condition. Washing with 0.5 M H2SO4 was the most effective regeneration method and the bio-modified catalyst regained 92% of its initial activity, while the corresponding value for the conventional catalyst was 111%. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 10. |
- Larsson, PO, et al.
(författare)
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Oxides of copper, ceria promoted copper, manganese and copper manganese on Al2O3 for the combustion of CO, ethyl acetate and ethanol
- 2000
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373. ; 24:3-4, s. 175-192
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Tidskriftsartikel (refereegranskat)abstract
- Combustion of CO, ethyl acetate and ethanol was studied over CuOx/Al2O3, CuOx-CeO2/Al2O3, CuMn2O4/Al2O3 and Mn2O3/Al2O3 catalysts. It was found that modification of the alumina with ceria before subsequent copper oxide deposition increases the activity for combustion of CO substantially, but the effect of ceria was small on the combustion of ethyl acetate and ethanol, The activity increases with the CuOx loading until crystalline CuO particles are formed, which contribute little to the total active surface, The CuOx-CeO2/Al2O3 catalyst is more active than the CuMn2O4/Al2O3 catalyst for the oxidation of CO but the CuMn2O4/Al2O3 catalyst is more active for the combustion of ethyl acetate and ethanol. Thermal ageing and water vapour in the feed caused a modest decrease in activity and did not affect the CuOx-CeO2/Al2O3 and CuMn2O4/Al2O3 catalysts differently. In addition, no difference in intermediates formed over the two catalysts was observed. Characterisation with XRD, FT-Raman and TPR indicates that the copper oxide is present as a copper aluminate surface phase on alumina at low loading. At high loading, bulk CuO crystallites are present as well. Modification of the alumina with ceria before the copper oxide deposition gives well dispersed copper oxide species and bulk CuO crystallites associated to the ceria, in addition to the two copper oxide species on the bare alumina. The distribution of copper species depends on the ceria and copper oxide loading. The alumina supported copper manganese oxide and manganese oxide catalysts consist mainly of crystalline CuMn2O4 and Mn2O3, respectively, on Al2O3 (C) 2000 Elsevier Science B.V. All rights reserved.
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