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Kinetics of the selective reduction of NO with NH3 over a V2O5(WO3)/TiO2 commercial SCR catalyst

Kamata, H; Takahashi, K and Odenbrand, Ingemar LU (1999) In Journal of Catalysis 185(1). p.106-113
Abstract
In order to clarify the mechanism of the selective catalytic reduction of nitric oxide with ammonia over a V2O5(WO3)/TiO2 commercial SCR catalyst, measurements were made on the reaction rate, r(NO), as a function of partial pressure of nitric oxide, P-NO, partial pressure of ammonia, P-NH3, and partial pressure of oxygen, P-O2, from 513 to 553 K under steady-state conditions. The adsorption of NO and NH3 on the catalyst was also observed by infrared spectroscopy (DRIFT). The apparent reaction orders with respect to NO were observed to be less than unity, 0.6-0.8. The reaction rate was nearly independent on P-NH3 at lower temperatures. As temperature increased, r(NO) became slightly increased with increasing P-NH3 at lower partial pressures... (More)
In order to clarify the mechanism of the selective catalytic reduction of nitric oxide with ammonia over a V2O5(WO3)/TiO2 commercial SCR catalyst, measurements were made on the reaction rate, r(NO), as a function of partial pressure of nitric oxide, P-NO, partial pressure of ammonia, P-NH3, and partial pressure of oxygen, P-O2, from 513 to 553 K under steady-state conditions. The adsorption of NO and NH3 on the catalyst was also observed by infrared spectroscopy (DRIFT). The apparent reaction orders with respect to NO were observed to be less than unity, 0.6-0.8. The reaction rate was nearly independent on P-NH3 at lower temperatures. As temperature increased, r(NO) became slightly increased with increasing P-NH3 at lower partial pressures of ammonia and tended to be saturated with further increases of P-NH3 The dependence of r(NO) on P-O2 was similar to that of P-NH3: r(NO) increased with increasing P-O2 at lower partial pressures of oxygen and was saturated with further increase of P-O2. The spectroscopic study showed that NO does not adsorb significantly on the oxidized nor on the NH3 preadsorbed surface of catalysts above at least 473 K. The SCR reaction was considered to proceed as follows. NH3 adsorbed on the Bronsted acid sites as ammonium ions. Ammonium ions were activated with the terminal oxygen groups, V5+=O, prior to the reaction with gaseous NO. Subsequent reaction with NO produced N-2, H2O, and the hydroxyl groups bonded to the reduced vanadium, V4+-OH, which would be reoxidized by oxygen to the V5+=O species. The Bronsted acid sites where NH3 adsorbed were then recreated. The results obtained in this study suggested that the Bronsted acid sites and/or the V5+=O species were equilibrated with the other species on the surface, implying that the number of each site changed with the experimental conditions such as P-O2. The relative amount of the V5+=O species would vary from similar to 0.1 to similar to 0.4 with increasing P-O2. (C) 1999 Academic Press. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Catalysis
volume
185
issue
1
pages
106 - 113
publisher
Elsevier
external identifiers
  • wos:000081135500009
  • scopus:0033169165
ISSN
1090-2694
DOI
10.1006/jcat.1999.2470
language
English
LU publication?
yes
id
406e134f-c054-40f3-99ba-9143ef0e184f (old id 3916326)
date added to LUP
2013-07-02 13:52:25
date last changed
2017-07-30 03:45:18
@article{406e134f-c054-40f3-99ba-9143ef0e184f,
  abstract     = {In order to clarify the mechanism of the selective catalytic reduction of nitric oxide with ammonia over a V2O5(WO3)/TiO2 commercial SCR catalyst, measurements were made on the reaction rate, r(NO), as a function of partial pressure of nitric oxide, P-NO, partial pressure of ammonia, P-NH3, and partial pressure of oxygen, P-O2, from 513 to 553 K under steady-state conditions. The adsorption of NO and NH3 on the catalyst was also observed by infrared spectroscopy (DRIFT). The apparent reaction orders with respect to NO were observed to be less than unity, 0.6-0.8. The reaction rate was nearly independent on P-NH3 at lower temperatures. As temperature increased, r(NO) became slightly increased with increasing P-NH3 at lower partial pressures of ammonia and tended to be saturated with further increases of P-NH3 The dependence of r(NO) on P-O2 was similar to that of P-NH3: r(NO) increased with increasing P-O2 at lower partial pressures of oxygen and was saturated with further increase of P-O2. The spectroscopic study showed that NO does not adsorb significantly on the oxidized nor on the NH3 preadsorbed surface of catalysts above at least 473 K. The SCR reaction was considered to proceed as follows. NH3 adsorbed on the Bronsted acid sites as ammonium ions. Ammonium ions were activated with the terminal oxygen groups, V5+=O, prior to the reaction with gaseous NO. Subsequent reaction with NO produced N-2, H2O, and the hydroxyl groups bonded to the reduced vanadium, V4+-OH, which would be reoxidized by oxygen to the V5+=O species. The Bronsted acid sites where NH3 adsorbed were then recreated. The results obtained in this study suggested that the Bronsted acid sites and/or the V5+=O species were equilibrated with the other species on the surface, implying that the number of each site changed with the experimental conditions such as P-O2. The relative amount of the V5+=O species would vary from similar to 0.1 to similar to 0.4 with increasing P-O2. (C) 1999 Academic Press.},
  author       = {Kamata, H and Takahashi, K and Odenbrand, Ingemar},
  issn         = {1090-2694},
  language     = {eng},
  number       = {1},
  pages        = {106--113},
  publisher    = {Elsevier},
  series       = {Journal of Catalysis},
  title        = {Kinetics of the selective reduction of NO with NH3 over a V2O5(WO3)/TiO2 commercial SCR catalyst},
  url          = {http://dx.doi.org/10.1006/jcat.1999.2470},
  volume       = {185},
  year         = {1999},
}