When the high-temperature automotive exhaust go through the purification device, the purifying agent in the catalytic converter will enhance the activity of the three harmful gases CO, HC and NOx, which make them acting oxidation - reduction reaction. CO oxidizes to a colorless, non-toxic gas CO2; HC compounds oxidize to H2O and CO2; NOx reduce to N2 and O2. The three harmful gases convert into harmless gases, which make the automobile exhaust purified.