Kinetics of the selective reduction of NO with NH{sub 3} over a V{sub 2}O{sub 5}(WO{sub 3})/TiO{sub 2} commercial SCR catalyst
- Ishikawajima-Harima Heavy Industries Co., Ltd., Yokohama (Japan). Research Inst.
- Lund Univ. (Sweden). Dept. of Chemical Engineering 2
In order to clarify the mechanism of the selective catalytic reduction of nitric oxide with ammonia over a V{sub 2}O{sub 5}(WO{sub 3})/TiO{sub 2} commercial SCR catalyst, measurements were made on the reaction rate, r{sub NO}, as a function of partial pressure of nitric oxide, P{sub NO}, partial pressure of ammonia, P{sub NH{sub 3}}, and partial pressure of oxygen, P{sub O{sub 2}}, from 513 to 533 K under steady-state conditions. The adsorption of NO and NH{sub 3} 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{sub NH{sub 3}} at lower temperatures. As temperature increased, r{sub NO} became slightly increased with increasing P{sub NH{sub 3}} at lower partial pressures of ammonia and tended to be saturated with further increases of P{sub NH{sub 3}}. The dependence of r{sub NO} on P{sub O{sub 2}} was similar to that of P{sub NH{sub 3}}; r{sub NO} increased with increasing P{sub O{sub 2}} at lower partial pressures of oxygen and was saturated with further increase of P{sub O{sub 2}}. The spectroscopic study showed that NO does not adsorb significantly on the oxidized nor on the NH{sub 3} preadsorbed surface of catalysts above at least 473 K. The SCR reaction was considered to proceed as follows. NH{sub 3} adsorbed on the Broensted acid sites as ammonium ions. Ammonium ions were activated with the terminal oxygen groups, V{sup 5+}{double_bond}O, prior to the reaction with gaseous NO. Subsequent reaction with NO produced N{sub 2}, H{sub 2}O, and the hydroxyl groups bonded to the reduced vanadium, V{sup 4+}{single_bond}OH, which would be reoxidized by oxygen to the V{sup 5+}{double_bond}O species. The Broensted acid sites where NH{sub 3} adsorbed were then recreated. The results obtained in this study suggested that the Broensted acid sites and/or the V{sup 5+}{double_bond}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{sub O{sub 2}}. The relative amount of the V{sup 5+}{double_bond}O species would vary from {approximately}0.1 to {approximately}0.4 with increasing P{sub O{sub 2}}.
- OSTI ID:
- 684568
- Journal Information:
- Journal of Catalysis, Vol. 185, Issue 1; Other Information: PBD: 1 Jul 1999
- Country of Publication:
- United States
- Language:
- English
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