Abstract: In this article, an optimum range for increasing transport coefficients with respect to the laminar flow condition in the channel of a three-way catalyst is introduced. A mathematical model of a three-way catalyst was first developed. The model is a one-dimensional plug flow model which involves mass and energy equations in gas and solid phases. To save numerical time, the three-way catalyst model was replaced with a neural network model used in optimization which was solved by using a multi-objective genetic algorithm method. The results of optimization introduce a range in which the desirable objectives will be satisfied. The objectives are to achieve minimum light-off time and maximum increase in catalyst efficiency during different operating conditions of engine.