Dissolution of Palladium and Platinum from Automotive Catalysts

Automotive exhaust gas catalysts contain palladium and platinum as the active material on an alumina substrate. Experiments were conducted to determine the amount of palladium and platinum that could be leached from fresh and aged automotive catalysts under various conditions. The conditions included soaking the catalyst samples in rain water to simulate environmental leaching from discarded catalysts and in dilute hydrochloric acid to simulate the dissolution of noble metals from swallowed catalysts. To obtain the necessary sensitivity for measuring microgram quantities of these noble metals in the leachates, radiochemical techniques were used. The results indicate that only very small amounts of noble metals are leached from fresh catalysts; the extent of dissolution depends upon catalyst pretreatment and the leaching solution. The dissolution of noble metals from aged catalysts (80,000-km vehicle tests) is one tenth that of fresh catalysts.