| It is well-known that automobile exhaust is a major cause of urban air pollution, and catalytic removal of pollutants has proven to be the most viable means of satisfying present environmental regulations. Carbon monoxide oxidation is a major automotive exhaust reaction. The kinetics of this reaction on three-way catalysts, preferred catalysts at present, are discussed in this thesis.; An experimental reactor system, based on the recycle reactor concept, was constructed to measure reaction kinetics. CO oxidation reaction was carried out in the presence of NO(,2), CO(,2), and H(,2)O at different temperatures and concentrations. The experimental data were analyzed for kinetic form and parameters, using the SIMPLEX optimization technique. Attendant diffusion-reaction equations were solved by employing orthogonal collocation technique. The bimolecular Langmuir-Hinshelwood kinetic form is found to represent the data satisfactorily.; Small amounts of SO(,2) present in the automotive exhaust are known to deactivate the catalyst considerably. To determine the extent of this poisoning effect, the reaction kinetics for CO oxidation were also measured in the presence of 20 ppm SO(,2) in the feed stream. The resulting rate expression showed a significant increase in activation energy, and an increased dependence on oxygen concentration. These changes are explained by including the effect of SO(,2) oxidation reaction. The range of SO(,2) concentrations employed in this set of experiments was relatively narrow. Experiments with a wider range of SO(,2) in the feed were also carried out, and were used to determine the poisoning kinetics. A Langmuir-Hinshelwood kinetic expression that included the temporary loss of active sites due to SO(,2) chemisorption was successfully developed to explain the observed kinetics.; The catalyst formulation used will be commercially viable only if it can satisfactorily remove nitrogen oxides as well, and the catalyst efficiency for doing this is strongly dependent on its selectivity for the CO-NO reaction over the CO-O(,2) reaction. The effect of this selectivity on CO and NO removal efficiency is calculated numerically using a simplified reactor model. Analytic expressions for the selectivity are also presented for special cases. |
