| 1. |
- Larsson, Ann-Charlotte, et al.
(författare)
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Physical and chemical characterisation of potassium deactivation of a SCR catalyst for biomass combustion
- 2007
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Ingår i: Topics in catalysis. - : Springer Science and Business Media LLC. - 1022-5528 .- 1572-9028. ; 45:1-4, s. 149-152
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Tidskriftsartikel (refereegranskat)abstract
- The deactivation of a commercial Selective Catalytic Reduction (SCR) catalyst, of V2O5-WO3/TiO2 type, has been studied through comparisons with results from a full-scale biomass combustion plant to that with laboratory experiments. In the latter, the catalyst was exposed to KCl and K2SO4 by both wet impregnation with diluted salt solutions and deposition of generated submicrometer aerosol particles by means of an electrostatic field. The reactivity of fresh and deactivated samples was examined in the SCR reaction. Chemical and physical characterizations were focusing on internal structures and chemical composition. Deposition of submicrometer sized particles on the monolithic SCR catalyst was shown to induce deactivation with characteristics resembling those obtained in a commercial biomass combustion plant.
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| 2. |
- Larsson, Ann-Charlotte, et al.
(författare)
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Targeting by Comparison with Laboratory Experiments the SCR Catalyst Deactivation Process by Potassium and Zinc Salts in a Large-Scale Biomass Combustion Boiler
- 2006
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 20:4, s. 1398-1405
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Tidskriftsartikel (refereegranskat)abstract
- The deactivation of a commercial selective catalytic reduction (SCR) catalyst of type V2O5−WO3/TiO2 has been studied in this work through comparisons of results from a full-scale biomass combustion plant with those from laboratory experiments. In the latter, the catalyst was exposed to KCl, K2SO4, and ZnCl2 by both wet impregnation with diluted salt solutions and deposition of generated submicrometer aerosol particles by means of an electrostatic field. The reactivity of freshly prepared and deactivated catalyst samples was examined in the SCR reaction, for which the influence of the different salts and the method of exposure were explored. Chemical and physical characterizations of the catalyst samples were carried out focusing on surface area, pore volume, pore size, chemical composition, and the penetration profiles of potassium and zinc. Particle-deposition deactivation as well as commercially exposed catalyst samples were shown to impact surface area and catalyst activity similarly and to have penetration profiles with pronounced peaks. Salt impregnation influenced pore sizes and catalyst activity more strongly and showed flat penetration profiles. Deposition of submicrometer-sized particles on the monolithic SCR catalyst has been shown to induce deactivation of the catalyst with characteristics resembling those obtained in a commercial biomass combustion plant; the laboratory process can be used to further assess the deactivation mechanism by biomass combustion.
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| 3. |
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| 4. |
- Andersson, Arne, et al.
(författare)
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A study of the ageing and deactivation phenomena occurring during operation of an iron molybdate catalyst in formaldehyde production
- 2006
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 112:1-4, s. 40-44
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Tidskriftsartikel (refereegranskat)abstract
- Catalyst from a Perstorp Formox formaldehyde plant, operating with high inlet concentration of methanol (10.2 vol.%), was discharged from single tubes of a multi-tube reactor after half the expected lifetime of the catalyst and again after termination of the load. Each tube was filled with two different layers of catalyst. From the inlet of the reactor the first layer was a catalyst mixed with inert rings, which was followed by a second layer of pure catalyst extending from the middle to the outlet of the reactor. Catalyst fractions from the two layers were characterized with various techniques including BET, Fourier transform Raman (FT-Raman) spectroscopy, X-ray diffraction (XRD), elemental analysis with atomic absorption spectroscopy (AAS) and activity measurements. It was found that the surface area of the catalyst in the mixed layer increases during operation while a small decrease is noticeable for the catalyst below in the pure layer. Elemental analysis, XRD and FT-Raman show that during operation of the catalyst there is migration of Mo species from the upper part of the reactor towards the outlet. Activity measurements reveal severe deactivation of the catalyst in the mixed layer. It is concluded that the deactivation primarily is due to formation of volatile species formed by the MoO3 surface reacting methanol, causing a decrease of the MoO3/Fe-2(MoO4)(3) mole ratio in the catalyst. Concerning the catalyst in the pure layer, the condensation of needle-like crystals of MoO3 mainly occurs on the external surface of the catalyst ring.
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| 5. |
- Andersson, Arne, et al.
(författare)
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Activities of V-Ti-O Catalysts in the Ammoxidation of 3-Picoline
- 1980
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 1090-2694 .- 0021-9517. ; 65:1, s. 9-15
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Tidskriftsartikel (refereegranskat)abstract
- Ammoxidation of 3-picoline was studied on reduced V-Ti-O catalysts with V6O13 as the major vanadium oxide. The results showed that the initial activity as a function of the TiO2 content reached a maximum at 50–60 mole% TiO2. It is proposed that there is maximum contact between the vanadium and titanium phases at this composition, which results in a weakening of the (VO)3+ surface bond. The selectivity of formation of nicotinonitrile exhibited a maximum of 83% at 10 mole% TiO2 and minima of 73 and 75% at 0 and 30 mole% TiO2, respectively. At higher TiO2 concentrations the selectivity increased continuously to 83% at 90 mole% TiO2. The variation of the selectivity of formation of nicotinonitrile depends on the View the MathML source ratio in the TiO2 phase. It was also found that the conversion and yields varied with the reaction time, which could be explained by the fact that reduced vanadium oxides were oxidized to V2O5 during the ammoxidation process. This oxidation leads to the formation of active and highly selective boundary surfaces between the TiO2-promoted vanadium oxides V6O13 and V2O5.
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| 6. |
- Andersson, Arne
(författare)
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Activities of V-Ti-O Catalysts in the Ammoxidation of 3-Picoline. II. Acid-Base Properties and Infrared Spectra
- 1982
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 1090-2694 .- 0021-9517. ; 76:1, s. 144-156
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Tidskriftsartikel (refereegranskat)abstract
- The acidity and basicity of prereduced V-Ti-O catalysts were measured by adsorption of NH3 and CO2. It was found that a high activity in the ammoxidation of 3-picoline corresponds to a relatively small amount of acidic sites. A catalyst selective in the formation of nicotinonitrile requires high concentrations of both acidic and basic sites. These results are discussed, and can be correlated if the acidity is considered to be a measure of the hydroxyl group concentration, and the basicity a measure of oxygen vacancies in the vicinity of VO groups. Also, the infrared spectra of the prereduced catalysts were recorded. A new band was found at 995 cm−1. The same band appeared in a homogeneous mixture of V2O5 and V6O13. It is proposed that this band can be assigned to VO bonds in a reduced V2O5phase with a number of disordered vacancies in the lattice, or a nonstoichiometric V6O13 phase. The shift in frequency relative to that of (VO)3+ shows that these bonds are weaker, and probably also more active. The effect of TiO2 is to increase the amount of V4+ in the vanadium oxide lattice. This is caused by dissolution of Ti4+ in the V2O5 melt during the catalyst preparation.
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| 7. |
- Andersson, Arne, et al.
(författare)
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Activities of Vanadium Oxides in Ammoxidation of 3-Picoline
- 1979
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Ingår i: Journal of Catalysis. - 1090-2694. ; 58:3, s. 383-395
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Tidskriftsartikel (refereegranskat)abstract
- Ammoxidation of 3-picoline to nicotinonitrile was studied on V2O5, V6O13, and V2O4 catalysts in a fixed-bed integral reactor. The activity studies showed that V6O13 was the most active and selective catalyst of the pure oxides, with a maximum yield of 76% nicotinonitrile at 365 °C. The maximum yield on V2O5 catalyst was 34%, and was obtained at a higher temperature, 458 °C. V2O4 was found to be inactive under the conditions studied. The activities and selectivities of the oxides changed rapidly with reaction time when V6O13 and V2O4 were studied. By means of X-ray diffraction and a titrimetric method, the average oxidation number of vanadium was determined, V6O13 was both oxidized and reduced during the reaction; V2O4 was oxidized, while a relatively smaller reduction of V2O5 could be detected. The experiments showed that the V6O13 catalyst used, with both V2O5 and V6O13 phases present, was more selective than any of the pure oxides. This may be explained by active boundary surfaces. Also a mechanism of formation of nicotinonitrile is proposed, which includes a step in which an adsorbed aldehyde complex reacts with ammonia.
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| 8. |
- Andersson, Arne, et al.
(författare)
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Ammoxidation of 3-Picoline: An Activity and High-Resolution Electron Microscopic Investigation of Vanadium Oxide Catalysts
- 1986
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Ingår i: Journal of Catalysis. - 1090-2694. ; 98:1, s. 204-220
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Tidskriftsartikel (refereegranskat)abstract
- A V2O5 catalyst was used in the ammoxidation of 3-picoline to nicotinonitrile. It was observed that the selectivity for the formation of CO2 as a function of temperature passed through a minimum. This is explained to be due to the existence of weakly bonded electrophilic oxygen species at low temperatures, and an increasing degradation involving O2− at high temperatures. A comparison of two different V2O5 preparations shows the beneficial effect of the V2O5(010) plane on the formation of nicotinonitrile. The exposure of planes other than the (010) plane as the source of formation of CO2 is discussed by consideration of bond strength values. The activity, selectivity, and composition of the charged V2O5 catalyst were followed as a function of time-on-stream at various temperatures. It was found that the V2O5 phase was reduced in the course of the reaction. V4O9, VO2(B), VO2 (tetragonal), and even more reduced phases were formed depending upon the reaction temperature used. Of the pure oxides, V4O9 was found to be both less active and less selective than V2O5. VO2(B), however, is more active but less selective compared to V2O5. The phases formed were characterized by various methods including high-resolution transmission electron microscopy (HRTEM). This technique made it possible to image the View the MathML source phase boundary for the first time. The general direction of this boundary is parallel to the (301) plane of V2O5. Micrographs of VO2(B) show that the nature of defects formed depends on the reaction temperature. After use at 695 K two types of planar twin lamellae were formed. At a slightly higher temperature partly amorphous defects appeared. The influence on the catalytic reaction of the phase boundaries and defects formed is discussed.
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| 9. |
- Andersson, Arne, et al.
(författare)
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Ammoxidation of toluene over molybdenum oxides
- 1988
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Ingår i: Catalysis Letters. - 1011-372X. ; 1:11, s. 377-383
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Tidskriftsartikel (refereegranskat)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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| 10. |
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