Micro-Kinetic Study Of Automobile Exhaust NO_x Emission Control

Motivated by increasing stringent legislation, automotive industry has lowered tailpipe pollutant emissions down to the order of centigrams per kilometer. Such levels of efficiency are not yet sufficient, however. Although great improvements have been made in catalytic converter technology, engine design and control systems, there still remains a lot to be done in several fields of automotive exhaust aftertreatment, in order to further reduce the emitted pollutants in urban areas. Since the core of almost every automotive exhaust aftertreatment system is some king of catalytic converter, intensive research activity is devoted to the various scientific and technical aspects of catalytic technology. These aspects vary from practical research on new materials and novel techniques to improve catalyst microstructure, to theoretical contributions of detailed descriptions of chemical phenomena inside the converters and proposals of mechanistic reaction schemes.The catalytic reduction methods of nitrogen oxides are reviewed in this paper, then we have developed an elementary reaction mechanism in order to comprehend the phenomena of catalytic reduction of NO by CO on platinum and rhodium catalysts. The pre-exponential factors are maintained at the order of magnitude estimates according to transition state theory. The activation energies of the elementary steps are found from the Unity Bond Index-Quadratic Exponential Potential (UBI-QEP) method. Then the reaction mechanism is coupled with the perfectly stirred reactor model and the simulation results are validated against literature experiments. Excellent agreement between our simulation results and literature experiments are observed for the NO-CO reaction on platinum and rhodium catalysts. The effect of temperature on the NO reduction activity is captured well by the model. Additionally the simulations can points towards effects of surface coverage on NO reduction. Eventually sensitivity analysis is performed to determine the importance elementary reactions in the NO-CO mechanism on platinum and rhodium catalysts. Then the NO oxidation reaction mechanism is coupled with detailed chemistry software DETCHEM^CHANNEL module. The results are compared to the experimental results. The results show that NO oxidation reaction mechanisms on Pt surface can successfully predict NO oxidation characteristics in this temperature range for both high and low metal dispersion catalysts.