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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

Björklund, RB; Andersson, Lars A H LU ; Odenbrand, Ingemar LU ; Sjöqvist, L and Lund, A (1992) In Journal of Physical Chemistry 96(26). p.10953-10959
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... (More)
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. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Physical Chemistry
volume
96
issue
26
pages
10953 - 10959
publisher
The American Chemical Society
external identifiers
  • wos:A1992KE71100064
  • scopus:0343020808
ISSN
0022-3654
DOI
10.1021/j100205a064
language
English
LU publication?
yes
id
161e3820-f143-46f2-b459-7c7013ddf7d6 (old id 3916382)
date added to LUP
2013-07-02 15:21:11
date last changed
2017-01-01 07:05:57
@article{161e3820-f143-46f2-b459-7c7013ddf7d6,
  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.},
  author       = {Björklund, RB and Andersson, Lars A H and Odenbrand, Ingemar and Sjöqvist, L and Lund, A},
  issn         = {0022-3654},
  language     = {eng},
  number       = {26},
  pages        = {10953--10959},
  publisher    = {The American Chemical Society},
  series       = {Journal of Physical Chemistry},
  title        = {Partial Reduction of a Vanadia/Silica-Titania Catalyst with NH3 + NO at 473 K Studied by Electrical Conductance and ESR Measurements},
  url          = {http://dx.doi.org/10.1021/j100205a064},
  volume       = {96},
  year         = {1992},
}