(33g) Experiments and Microkinetic Modelling of NO Reduction Using HC-SCR on Ag Catalyst

We propose in this work lab scale experiments and microkinetic modelling for the reduction of NO under automotive exhaust conditions, using Ag based catalysts. A detailed microkinetic model is developed for the HC-SCR, choosing propene as the reductant and Ag/Al₂O₃ as the catalyst.In the laboratory setup, cold gases from the cylinders are passed through the mass flow controller to the preheater. The preheated gases are then sent to the packed bed reactor loaded with the silver catalysts (5% Ag/Al₂O₃₎ inside a quartz glass tube located in the furnace. The outlet from the reactor is sent to the chemiluminescent detector (CLD) where the outlet NO_xconcentration is measured.

The microkinetic model developed consists of 56 elementary reactions including several adsorption, desorption and surface reaction steps. The Unity Bond Index-Quadratic Exponential Potential (UBI-QEP) method [1] is used to calculate the activation energies of the elementary reactions. Order of magnitude estimates of pre-exponential factors are taken from transition state theory as in previous results.

The microkinetic simulations are performed using the CHEMKIN software package, assuming an ideal plug flow reactor. The effect of varying inlet concentration of O₂ on the outlet NO conversion is examined. The reactor temperature is held in the range of (200-650) ⁰C, in both lab-scale experiments and computer simulations. The results from microkinetic simulations and experiments are compared. Evidence of several interesting operational regimes is expected as the O₂concentration is varied.

References

[1] E. Shustorovich, A. Bell, T. Surf. Sci., 248, 1991, 359−368.