An Investigation of Poison Deactivation on Palladium Based Three Way Catalyst

This paper discusses the effect of poisons originated from the engine oil and fuel on the catalytic activity of palladium based close coupled catalysts. The performances of seven aged catalysts were analyzed by synthesized gas activity tests. The effects of thermal deactivation of the catalyst were investigated by BET surface area and X-ray diffraction tests. To show the poisoning effects along the exhaust stream, the additives of oil and fuel were quantified by ICP spectrometry and x-ray flouresences (XRF). SEM-EPMA analysis were also performed to determine the distribution of poisons in the washcoat. The contribution of poisoning to the overall deactivation process could than be estimated by comparing the results before and after leaching the poisonous elements with a weak acid solution. Test results show the activity of the palladium based catalysts can be severely deteriorated by poisons. Formation of the diffusion barriers composed of P, Ca, Zn can hinder the mass transfer process. Phosphorous compounds such as aluminum phosphate can also lead to activity loss, however CePO₄ was not detected in any of our catalyst. From the engine bench tests and vehicle tests, it was found that sulfur deactivation causes a severe activity loss of our Pd based close coupled catalysts under fuel rich A/F condition.