Catalytic converters (automotive catalysts) and the chemical reactions they catalyze appear in general and introductory chemistry textbooks. Although the detailed mechanisms of the chemical reactions that occur in catalytic converters have been clearly revealed via recent developments in surface and computational chemistry research, the description and illustration of the catalysis are still ambiguous in textbooks. In this paper, we describe an extracurricular lecture whereby a handmade teaching aid was employed to illustrate the basic principle of the catalytic oxidation of carbon monoxide over platinum surface, which is an essential reaction occurring in catalytic converters. The teaching aid, constructed combining easily available materials, can illustrate the positions and motions of the molecules on the platinum surface during catalytic oxidation. The lecture was favorably received by non-chemistry majors and high school students. Despite the difficulty of the topic, the audience displayed a relatively high level of understanding.