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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
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| 7. |
- Andersson, Arne
(författare)
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An Oxidized Surface State Model of Vanadium Oxides and Its Application to Catalysis
- 1982
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596. ; 42:3, s. 263-275
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Tidskriftsartikel (refereegranskat)abstract
- The charge distribution around the VO bonds in V2O5, V6O13, and V2O4 was calculated by using an empirical formula. The same expression was also used to calculate the oxygen bond strengths on the surface. The surfaces of lower oxides were treated as though they were in an oxidized state which is believed to correspond to the conditions in oxidation and ammoxidation processes. The result is that O2−, in the form of VO surface groups, is responsible for the catalytic oxidation of hydrocarbons. O− is hindered by the formation of stable OH− groups. The positions of lower valent oxygens are considered to be vacant because of a slow reoxidation rate. In V2O5 the VO groups are located on the (010) plane, while in V6O13 they are mainly located on the (001) surface plane. But in this case the (100) and (010) surface planes also have some VO groups. The catalytic activity of the rutile form of V2O4 is limited by sterical factors, but the (110) surface plane has oxygens pointing perpendicular out of the surface.
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| 8. |
- Andersson, Arne, et al.
(författare)
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Catalytic Anisotropy of MoO3 in the Oxidative Ammonolysis of Toluene
- 1988
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 1090-2694 .- 0021-9517. ; 114:2, s. 332-346
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Tidskriftsartikel (refereegranskat)abstract
- The oxidative ammonolysis of toluene, i.e., ammoxidation without the presence of molecular oxygen, was studied over a series of samples of MoO3 crystals. The specific surface areas of the various faces were determined from SEM micrographs. Correlations between activities and surface planes were found. For the formation of nitrile the specific activity decreased in the order {001} and {h01} > {100} > {010}. Also, for the formation of carbon oxides the terminations in the [001] direction were found to be especially active. These results are discussed in relation to surface structures and bond strength values of various oxygen species. It is concluded that the presence of both oxygen vacancies and nucleophilic oxygen species is a prerequisite for selective reaction to occur and that electrophilic oxygen species are the source for formation of carbon oxides. The characteristics of the various faces, as they emerge from the results on oxidative ammonolysis of toluene, seem to be of general significance for reactions occurring at the same types of active sites. They are shown to be applicable to results published in the literature on the oxidation of both propene and isobutene.
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| 9. |
- Andersson, Arne
(författare)
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Structural Dynamics of a V2O5/SnO2 Catalyst in the Ammoxidation of 3-Picoline
- 1981
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 1090-2694 .- 0021-9517. ; 69:2, s. 465-474
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the reaction parameters on the conversion of 3-picoline and the yield of nicotinonitrile in the ammoxidation of 3-picoline on a View the MathML source catalyst was studied. The highest yield of nicotinonitrile was 82%. This was obtained at 400 °C, with a space velocity of 4000 h−1 and the following mole ratios: ammonia/3-picoline = 12, air/3-picoline = 210, and water vapour/3-picoline = 40. It was found that the composition of the surface of the catalyst depended strongly on the values of the reaction parameters. The dynamic structure of the catalyst surface was studied by determining the phases present by X-ray diffraction analysis and the average oxidation number of vanadium by titrimetric methods. These results were correlated, showing that catalysts with both V2O5 and V6O13 were especially active and selective. The composition of the SnO2 phase was analyzed and was found to be V0.03Sn0.97O2, and did not depend on the reaction parameters. Infrared investigations showed that the role of SnO2 was to weaken the short VO bonds. This can probably be seen as a consequence of incorporation of Sn4+ in the V2O5 lattice.
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| 10. |
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