The study is motivated by a review of experimental and numerical evidence for the existence of bistability and hysteresis in CO oxidation on platinum group metals. In this paper, a detailed taxonomy of CO oxidation on Pd(111) is achieved by considering it as classification problem of hysteresis functions. This consideration offers a way of classifying the hysteresis behavior into several types using the mathematics of finite state automata, and in this way a through classification is achieved. The classification can provide a global framework for understanding the hysteresis behavior of CO oxidation reaction on Pd(111).