Volatile Phosphorus Generation for Catalyst Poisoning Using FOCAS®, 03-R8047

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Principal Investigators
Crystal Fierro
Michael Hedge

Inclusive Dates:  04/01/09 – 10/01/10

Background - SwRI's FOCAS® System is a gasoline-fueled burner developed for exposing catalysts to multiple variables in a well-controlled environment to determine long-term effects on catalyst performance. Previously, engine field tests and dynamometer tests have been used to perform catalyst aging and oil poisoning. However, with the introduction of the FOCAS system, burners can now be used to perform accelerated catalyst aging and oil poisoning with precise control over oil exposure. This project focused on expanding the FOCAS system's capability of replicating real-world engine oil consumption. It is well understood that engine oil constituents, such as phosphorus, are catalyst poisons and lead to irreversible degradation in catalyst performance. However, in recent years it has been determined that the volatile component phosphorus of the oil's anti-wear/oxidation package Zinc Diakyldithiophosphate (ZDDP) plays a major role in catalyst oil poisoning. With two pathways for oil poisoning, bulk and volatile, it is important to analyze the effects of both the amount of phosphorus in the bulk oil and the volatility of the ZDDP additive package on catalyst poisoning.

Approach - This investigation was divided into two phases. Phase I consisted of finalizing the design and fabricating the volatile oil injection subsystem. It also included developing oil volatilization theories and test procedures intended to mimic trends observed on actual test vehicles. Phase II consisted of two tests run on a dual exhaust FOCAS system using two different oils. The first test used oil containing conventional ZDDP. Bulk and volatilized oil were simultaneously injected into the first leg of the exhaust, while only bulk oil was injected into the second leg. The second test introduced low volatility ZDDP oil via bulk and volatized injection into the first leg of the exhaust system. The second exhaust leg was used for thermal aging only and did not have any oil injection. The purpose of this test was to demonstrate the system's ability to discriminate between standard and low volatility ZDDP formulations by noting the differences in phosphorus poisoning seen on the catalysts as well as accounting for any thermal aging. All the catalysts of Phase II were subjected to stoichiometric, perturbated light-off tests, proton induced X-ray emission (PIXE) elemental analysis and BET surface area/pore volume measurements.

Accomplishments - After reviewing all of the results from the tests, it is clear that the project was successful in characterizing oil volatilization of a vehicle in the field as well as recreating the oil consumption profile with the FOCAS system. The physical, chemical and activity characteristics of the exposed catalysts matched with anticipated levels exceptionally well, and with previous laboratory and field experience. The phosphorus retention levels measured during the mileage accumulation study were replicated during the FOCAS testing, as verified by the oil analysis from each oil change during the aging. Moreover, the oil analysis indicated a clear differentiation between the phosphorus volatility of Oil A and B. N2 adsorption measurements confirmed a decrease in BET surface area and pore volume with increased level of phosphorous deposition for all catalysts exposed to oil, consistent with pore blocking. The investigation has advanced the capabilities of the commercially available FOCAS system and should provide new opportunities to expand its scope of work to oil additive manufacturers as well as catalyst suppliers.

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