Abstract
CO and C3H6 oxidation have been carried out in the absence and presence of water over a Pd/Al2O3 catalyst. It is clear that water promotes CO and, as a consequence, C3H6 oxidation takes place at much lower temperatures compared with the dry feed. The significant increase in the catalyst's activity with respect to CO oxidation is not simply associated with changes in surface concentration as a result of competitive adsorption effects. Utilising 18O2 as the reactant allows the pathways whereby the oxidation due to gaseous dioxygen and where the water activates the CO and C3H6 to be distinguished. In the presence of water, the predominant pathway is via water activation with C16O2 and C16O18O being the major species formed and oxidation with dioxygen plays a secondary role. The importance of water activation is further supported by the significant decrease in its effect when using D2O versus H2O.
Highlights
With demands for increased fuel efficiency growing, the interest in diesel engines for passenger vehicles has expanded
They oxidize NO to NO2 which plays an important role in enhancing the performance of downstream catalysts, such as selective catalytic reduction (SCR) catalysts, lean NOx traps (LNTs) and
It was reported that the apparent activation energy of the CO oxidation decreased when water was included in the feed
Summary
With demands for increased fuel efficiency growing, the interest in diesel engines for passenger vehicles has expanded. Diesel oxidation catalysts (DOC) are used to remove hydrocarbons (HC) and carbon monoxide from diesel engines [1] and the DOCs employed can achieve more than 90% reduction in CO and HC emissions at exhaust temperatures higher than ∼300 ◦C [2] They oxidize NO to NO2 which plays an important role in enhancing the performance of downstream catalysts, such as selective catalytic reduction (SCR) catalysts, lean NOx traps (LNTs) and. The effect of water on CO and C3H6 oxidation activities under lean conditions was investigated and the reaction mechanism probed using isotope experiments Understanding these effects are important in order to clarify the reactions which occur over a diesel oxidation catalyst in practical operation
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