The kinetics of the oxidation of ammonia on a V2O5/TiO2 SCR catalyst deactivated in an engine rig. Part I. Determination of kinetic parameters by simulation

Abstract

It is shown how the deactivation of a diesel SCR (Selective Catalytic Reduction) catalyst by compounds in the exhaust gases influences the kinetics of the catalyst. Results are given for the fresh (4.56 % V₂O₅/TiO₂) catalyst and the ones used in the rig for 890 h and 2299 h. The reactions of 700 ppm NH₃ and 2 % O₂ in Helium yielded N₂, N₂O, and NO at increasing temperatures. Simulations were performed with COMSOL Multiphysics using a 3-D model of the catalyst system. The experimental values of the products N₂, N₂O, and NO were very nicely fitted by the kinetic model used. All three ammonia oxidation reaction rates were of the first order in the concentration of NH₃. A preliminary study using non-isothermal conditions showed the maximal temperature increase to be 0.15 K. Thus, further simulations were done with an isothermal model. The deactivation reduces the pre-exponential factors and the activation energies for the formation of N₂, N₂O, and NO. The formation of N₂ is not substantially influenced by deactivation. The changes in the kinetics of the catalytic NH₃ oxidation by deactivation is reported for the first time in the present study.

Keywords

• Oxidation of ammonia,poisoning and kinetics,Vanadia SCR diesel catalysts

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