The kinetics of the oxidation of ammonia on a $V_2O_5/TiO_2$ 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 exhaustgases influences the kinetics of the catalyst. Results are given for the fresh (4.56 % $V_2O_5/TiO_2$) catalyst and the onesused in the rig for 890 h and 2299 h. The reactions of 700 ppm $NH_3$ and 2 % $O_2$ in Helium yielded $N_2$, $N_2O$, and NO atincreasing temperatures. Simulations were performed with COMSOL Multiphysics using a 3-D model of the catalystsystem. The experimental values of the products $N_2$, $N_2O$, and NO were very nicely fitted by the kinetic model used. Allthree ammonia oxidation reaction rates were of the first order in the concentration of NH3. A preliminary study usingnon-isothermal conditions showed the maximal temperature increase to be 0.15 K. Thus, further simulations were donewith an isothermal model. The deactivation reduces the pre-exponential factors and the activation energies for theformation of $N_2$, $N_2O$, and NO. The formation of $N_2$ is not substantially influenced by deactivation. The changes in thekinetics of the catalytic $NH_3$ oxidation by deactivation is reported for the first time in the present study.