Abstract
Platinum group metals such as palladium and rhodium based catalysts are currently being implemented in gasoline particulate filter (GPF) autoexhaust after treatment systems. However, little is known about how the trapped particulate matter, such as the incombustible ash, interacts with the catalyst and so may affect its performance. This operando study follows the evolution of the Pd found in two different model GPF systems: one containing ash components extracted from a GPF and another from a catalyst washcoat prior to adhesion onto the GPF. We show that the catalytic activity of the two systems vary when compared with a 0 g ash containing GPF. Compared to the 0 g ash sample the 20 g ash containing sample had a higher CO light off temperature, in addition, an oscillation profile for CO, CO2 and O2 was observed, which is speculated to be a combination of CO oxidation, C deposition via a Boudouard reaction and further partial oxidation of the deposited species to CO. During the ageing procedure the washcoat sample reduces NO at a lower temperature than the 0 g ash sample. However, post ageing the 0 g ash sample recovers and both samples reduce NO at 310 °C. In comparison, the 20 g ash GPF sample maintains a higher NO reduction temperature of 410 °C post ageing, implying that the combination of high temperature ageing and presence of ash has an irreversible negative effect on catalyst performance.
Highlights
The surge in the use of light-duty vehicles transport has resulted in increased air pollution through the combustion of fuels
We study the effect of the manufacturing process on the catalyst activity evaluated through the comparison of the catalytic activity of the fresh washcoat with a sample extracted from a gasoline particulate filter (GPF) with no ash deposition (0 g GPF)
It was initially predicted that the Pd species would be more akin to PdO, though a reason for this initial difference in Pd speciation could be due to the manufacturing process of GPFs, where the catalyst washcoat undergoes high calcination temperatures to adhere onto the monolith channel walls and allow for decomposition of metal precursor compounds
Summary
The surge in the use of light-duty vehicles transport has resulted in increased air pollution through the combustion of fuels. Over the lifespan of the GPF, the system may experience excursion temperatures around 1000 ◦C [25, 26] With this in mind, it is important to understand how the catalytic system activity changes both on the incorporation of ash components and at these extremely high temperatures. No XANES data were reported above light-off temperatures, i.e. above 300 ◦C and no data given on the catalytic activity of the washcoat prior to incorporation onto the monolith [30] To understand these key effects of high temperatures on the ash loaded GPF TWC system, and on the effect that the manufacturing of the GPF plays on the performance of the catalyst, here we investigate an industrial GPF model catalyst based on a PdRh/CeZrO2/Al2O3 catalyst. The CO oxidation, NO reduction and propane consumption profiles were followed and compared with the profile of a sample extracted from the 0 g ash GPF sample, in order to determine the role of the ash on the activity of the catalyst and the effect the GPF production plays on the activity of the initial catalyst formulation
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