Low Volatility ZDDP Technology: Part 2 - Exhaust Catalysts Performance in Field Applications

Phosphorus is known to reduce effectiveness of the three-way catalysts (TWC) commonly used by automotive OEMs. This phenomenon is referred to as catalyst deactivation. The process occurs as zinc dialkyldithiophosphate (ZDDP) decomposes in an engine creating many phosphorus species, which eventually interact with the active sites of exhaust catalysts. This phosphorous comes from both oil consumption and volatilization. Novel low-volatility ZDDP is designed in such a way that the amounts of volatile phosphorus species are significantly reduced while their antiwear and antioxidant performances are maintained.

A recent field trial conducted in New York City taxi cabs provided two sets of “aged” catalysts that had been exposed to GF-4-type formulations. The trial compared fluids formulated with conventional and low-volatility ZDDPs. Results of field test examination were reported in an earlier paper (1). As a part of our current examinations, Federal Test Procedure (FTP-75) emissions tests were conducted. Emissions data collected showed a statistically significant difference in 50% hydrocarbon (HC) efficiency light-off time, on low impact ZDDP as compared to conventional ZDDP, and an even greater effect on nitrogen oxides (NOx) and carbon monoxide (CO) emissions due to a reduction in the phosphorus-derived catalyst deactivation.