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- Björklund, RB, et al.
(författare)
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Partial Reduction of a Vanadia/Silica-Titania Catalyst with NH3 + NO at 473 K Studied by Electrical Conductance and ESR Measurements
- 1992
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Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 96:26, s. 10953-10959
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Tidskriftsartikel (refereegranskat)abstract
- Partial reduction of vanadia supported on silica-titania by NH3 + NO has been studied by electrical conductance and ESR measurements. The relationship between electrical conductance and degree of reduction was determined by oxidative and reductive titrations of V(IV) and V(V) species leached from catalyst samples which had been reduced to different levels. In situ monitoring of the steady-state V(IV) ion concentration by electrical conductance during reduction with NH3 + NO in the concentration range 0-600 ppm for each reactant in a 2 vol % O2/Ar carrier gas was performed. In a large excess of NH3, the V(IV) ion concentration increased sharply with even small additions of NO. In a large excess of NO, the NH3 + NO mixture exhibited first an oxidizing character, and the V(IV) ion concentration increased when P(NH3) > 1/6P(NO). The reaction order with respect to the NO concentration, determined from both the NO conversion and the initial rate of catalyst reduction in excess NH3, was found to be less than unity. Determination of the stoichiometry of the reaction with respect to O2 indicated that the gas-phase O2 concentration required to balance the reducing character of NH3 + NO mixtures on the surface was significantly higher than predicted by the balanced equation describing the reaction. ESR measurements on the catalyst detected V(IV) ions as vanadyl groups having two different coordination spheres. Reduction of the catalyst with NH3 + NO caused an increase in the V(IV) signal and a decrease of the hyperfine structure.
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| 5. |
- Holst, LE, et al.
(författare)
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Investigation of peat pyrolysis under inert gas atmosphere
- 1991
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 70:9, s. 1017-1022
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Tidskriftsartikel (refereegranskat)abstract
- Seven Swedish peats of different degrees of humification were pyrolysed in a thermobalance at pressures in the range 1.0-4.0 MPa. The formation kinetics of the pyrolysis products were determined using the non-isothermal evaluation method. The sample size used was 1.0 g and the heating rate was 10 K min-1. Gas production was analysed by gas chromatography and the components were CO2, C2H4, C2H6, CH4 and CO. The tar and char production were measured after the experiment by weighing. The experiments showed that gas production was slightly increased, at the expense of tar production, with increasing pressure, indicating some thermal cracking. The kinetic parameters, i.e. pre-exponential factor, k0, and activation energy, E(a), were unaffected by the pressure.
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| 7. |
- Odenbrand, Ingemar, et al.
(författare)
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Effect of water vapour on the selectivity in the reduction of nitric oxide with ammonia over vanadia supported on silica-titania
- 1991
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Ingår i: Applied Catalysis. - 0166-9834. ; 78:1, s. 109-123
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the presence of water vapor on the reduction of nitric oxide with ammonia was investigated using vanadia on SiO2-TiO2 as a catalyst. The selectivity towards nitrogen is greatly increased upon addition of water. Repeated use at temperatures of 825 K causes sintering of the catalyst and loss of activity as well as selectivity towards nitrogen. The formation of nitrous oxide is preferentially taking place on large crystals of presumably reduced vanadia. Removal of these crystals results in a more selective catalyst.
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