Phosphorous Poisoning and Phosphorous Exhaust Chemistry with Diesel Oxidation Catalysts

Phosphorous in diesel exhaust is derived via engine oil consumption from the zinc dialkyldithiophosphate (ZDDP) oil additive used for engine wear control. Phosphorous present in the engine exhaust can react with an exhaust catalyst and cause loss of performance through masking or chemical reaction. The primary effect is loss of light-off or low temperature performance. Although the amount of ZDDP used in lube oil is being reduced, it appears that there may is a minimum level of ZDDP needed for engine durability. One of the ways of reducing the effects of the resulting phosphorous on catalysts might be to alter the chemical state of the phosphorous to a less damaging form or to develop catalysts which are more resistant to phosphorous poisoning.

In this study, lube oil containing ZDDP was added at an accelerated rate through a variety of engine pathways to simulate various types of engine wear or oil disposal practices. In all cases, the phosphorous was found in the engine exhaust with the form and chemistry varying according to the method of introduction. Diesel oxidation catalysts run under these conditions of oil introduction showed phosphorous poisoning and masking effects as measured by light-off characteristics and material and chemical property changes. The form of deposition of phosphorous on the catalyst varied with method of introduction. The amount of performance loss found was similar. The analytical techniques and testing procedures developed can be related to field aging rates and can be also used as a means to rapidly screen additives or catalysts for phosphorous poisoning behaviors.