| 1. |
- Lu, H, et al.
(författare)
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Catalytic reduction of nitric oxide over copper Part III : Influence of water vapour
- 1999
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Ingår i: Journal of Molecular Catalysis A. - 1381-1169 .- 1873-314X. ; 138:2-3, s. 227-236
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on the effect of water vapour on the reduction of NO over copper in the presence of oxygen and isobutene. Reactions were studied at 700 K and at 770 K. Mass spectroscopy (MS) and X-ray photoelectron spectroscopy (XPS) were used to monitor the gas phase composition during reaction and to analyse the catalyst surface, respectively. XPS spectra show that the presence of water vapour influences the Cu oxidation state. At 700 K adsorption of aldehyde is partly blocked by copper oxide resulting in a decrease in the activity of the reaction, although the main mechanism is not changed. At 770 K, water vapour generates an even more oxidised surface, which promotes a complete oxidation of hydrocarbon, the main mechanism of NO reduction is changed, and the activity of the reaction is slightly increased. (C) 1999 Elsevier Science B.V. All rights reserved.
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| 2. |
- Borowiak, MA, et al.
(författare)
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Catalytic decomposition of formic acid on oxide catalysts - an impulse-oscillation model approach to the unimolecular mechanism
- 1999
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Ingår i: Journal of Molecular Catalysis A: Chemical. - 1381-1169. ; 139:1, s. 97-104
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Tidskriftsartikel (refereegranskat)abstract
- An impulse-oscillation model (IOM) was used for a time description of catalytic acts in the reactions of catalytic decomposition of formic acid on oxide catalysts. The results of computation using the model show that for the dehydrogenation reaction the most important modes are the OCO bending in bidentate adsorbed formate ion and OH stretching on the catalyst surface while for the dehydration the asymmetric stretching OCO mode in the monodentate adsorbed formate ion and metal-oxygen stretching mode on oxide catalysts. These findings confirm the results obtained [R. Larsson, M,H. Jamroz, M.A. Borowiak, J. Mel. Catal. A: Chem. 129 (1998) 41] in our previous analysis of the SET model. Assuming the synchronization of eight vibrators to be important in the reactions system considered in the present paper, the IOM method predicted ranges of wavenumbers which are close to those wavenumbers found starting from the idea of a stepwise variation of activation energies. The best ranges for the dehydrogenation reaction are proposed. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
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| 3. |
- Kamata, H, et al.
(författare)
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The role of K2O in the selective reduction of NO with NH3 over a V2O5(WO3)/TiO2 commercial selective catalytic reduction catalyst
- 1999
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Ingår i: Journal of Molecular Catalysis A: Chemical. - 1381-1169. ; 139:2-3, s. 189-198
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Tidskriftsartikel (refereegranskat)abstract
- To elucidate the nature of the acid sites of the V2O5(WO3)/TiO2 catalyst upon K2O addition and its relation to the selective reduction of NO with NH3, measurements were made by means of infrared and Raman spectroscopy, NH3 chemisorption, and NO reduction measurements as a function of the K2O loading. The catalytic activity was found to decrease rapidly with the K2O loading, irrespective of the similar textural properties of all samples. Addition of K2O modified the vanadium species on the catalyst surface. For large additions of K2O, the potassium partially reacted with V2O5 to form KVO3. The amount of NH3 chemisorbed on the catalyst was observed to decrease with both the loading of K2O and the temperature. The adsorption of NH3 on both Bronsted and Lewis acid sites was confirmed. The strength and the number of Bronsted acid sites decrease largely with the loading of K2O in parallel with the decrease of the SCR activity, suggesting that the SCR reaction involves NH3 adsorption on the Bronsted acid sires. At low surface coverage of NH3, the isosteric heat of NH3 chemisorption was determined to be 370 kJ/mol for 0 wt.% K2O addition. With increasing K2O amount, the heat of adsorption decreased and was 150 kJ/mol for the catalyst with higher amounts of K2O addition. The results obtained imply that potassium disturbs the formation of the active ammonia intermediates, NH4+, resulting in deactivation of the catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.
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