Abstract
In the present study, two industry primary and secondary zinc dialkyldithiophosphate standards, ZDDP1 and ZDDP2, respectively, are evaluated for their impact on the performance of Pd-based three-way catalyst and bench-marked against two mixed lubricant additives formed from either ZDDP1 or ZDDP2 with a second-generation oil-miscible phosphoric-containing ionic liquid (IL). The three-way catalysts (TWCs) are exposed to the lubricant additives in an engine bench under four different scenarios: a base case with no additive (NA), ZDDP1, IL+ZDDP1, ZDDP2, and IL+ZDDP2. The engine-aged TWC samples are characterized through a variety of analytical techniques, including evaluation of catalyst reactivity in a bench-flow reactor. With respect to the water–gas shift reaction and the oxygen storage capacity, the ZDDP2- and IL+ZDDP2-aged TWC samples are more degraded than the ZDDP1- and IL+ZDDP1-aged TWC samples. X-ray diffraction (XRD) patterns indicate that phosphorus in the form of CePO4 was found to be present in the washcoat of all TWC samples, with the highest amount found in the ZDDP2-aged TWC sample. The results obtained from XRD are further confirmed by those from inductively coupled plasma-optical emission spectroscopy (ICP-OES), which show that more phosphorus is detected in the washcoat of ZDDP2- and IL+ZDDP2-aged TWC samples than in the ZDDP1- and IL+ZDDP1-aged TWC samples.
Highlights
Zinc dialkyldithiophosphate (ZDDP) has long been widely used as a lubricant additive because of its high anti-friction and anti-wear effects in engines
Bench-Flow Reactor (BFR) experiment results reveal that the performance of the threeway catalysts (TWCs) is degraded further by ZDDP1, ZDDP2, ionic liquid (IL)+ZDDP1, and IL+ZDDP2 lubricant additives as compared to that of NA-aged TWC sample, indicating the additional impact of poisoning from lubricant additives
Even though the P dosage is kept constant throughout the accelerated poisoning experiment, the difference in the amount of P obtained from electron probe microanalysis (EPMA) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) is possibly due to the difference in the P volatility of ZDDP1 and ZDDP2
Summary
Zinc dialkyldithiophosphate (ZDDP) has long been widely used as a lubricant additive because of its high anti-friction and anti-wear effects in engines. ZDDP is classified either as primary or secondary, depending on the type of alcohol used in the manufacturing process [1]. The more reactive secondary alkyl ZDDP is used for gasoline engines, while primary alkyl ZDDP with high thermal stability is used for diesel engines [1,2]. The main components of ZDDP, such as zinc (Zn), phosphorous (P), and sulfur (S), have been shown to form ash during engine combustion, causing significant deactivation of the threeway catalysts (TWCs). Zn2 P2 O7 was formed directly on the washcoat surface, causing site deactivation of the TWCs [3,4]. The formation of cerium orthophosphate, CePO4 , has been identified within the catalyst washcoat [5,6,7,8,9,10]
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