Ann E. O'Neill

Observation of Strained PdO in an Aged Pd/Ceria-Zirconia Catalyst

A model automotive-exhaust catalyst, Pd on Zr-rich ceria–zirconia, was characterized by X-ray diffraction, optical and electron microscopies, and micro-Raman spectroscopy following high-temperature aging. A broad bimodal distribution of Pd, introduced amongst the 10-μ m spherical particles of support material during catalyst preparation, was found to persist upon aging, and strained PdO was detected predominantly in those particles containing the higher concentration of Pd. The strain, approximately -1% by volume, was determined from the shift of the strong PdO Raman line at 650 cm-1 and the Grüneisen parameter, which was measured in a separate experiment in a diamond-anvil cell. The origin of the compressive stress that gives rise to this strain is believed to be the same as in the previously known phenomenon of Pd–metal encapsulation, but the Pd particles involved here are apparently not highly constrained within the sintered ceria–zirconia matrix prior to their oxidation.

Comparison of the Effects of Biodiesel and Mineral Diesel Fuel Dilution on Aged Engine Oil Properties

Dilution of engine oil occurs when fuel is injected late in the combustion cycle to regenerate the diesel particulate filter used for trapping particulate emissions. Fuel dilution reduces oil viscosity and the concentration of engine oil additives, potentially compromising lubricant performance. Biodiesel usage may compound these issues due to its oxidative instability, and its higher boiling point compared to mineral diesel potentially causes it to concentrate more in the oil sump. In this work, different amounts of mineral diesel and biodiesel (soy methyl ester, SME) were combined with 15W-40 CJ-4 diesel engine oil in laboratory oil aging experiments. Fuel was added and oil samples were withdrawn at periodic intervals. The oils were analyzed using typical oil analysis procedures to determine their condition, and wear evaluations under boundary lubricating conditions were determined using a high-frequency reciprocating rig (HFRR). Results showed that fuel dilution accelerated engine oil degradation, with biodiesel having a larger effect. However, friction remained unchanged with dilution, and wear actually decreased for fuel-diluted oils after 48 h of aging compared to aging without fuel dilution. Examination of the tribofilms by ultraviolet (UV) and visible Raman spectroscopy as well as Auger electron spectroscopy showed that additional carbon-containing components were present on tribofilms formed from fuel-diluted oils. These fuel-derived components may be responsible for the decreased wear observed.