| Summary: | Hydrocarbon traps for exhaust emissions control adsorb hydrocarbons in low temperature exhaust and release them as the exhaust warms up. In this work, a Pd/BEA hydrocarbon trap was tested under lean exhaust conditions using ethylene and dodecane as model hydrocarbons. Ethylene uptake was partially inhibited by CO and H<sub>2</sub>O when fed separately. When both were added, the loss in ethylene uptake was 90% relative to the condition with no H<sub>2</sub>O or CO. Dodecane uptake was unchanged under all conditions tested. During a temperature ramp, ethylene desorbed and was combusted to CO<sub>2</sub> and H<sub>2</sub>O over active Pd centers. Further, oxidation light-off of dodecane generated an exotherm which caused rapid desorption of the remaining hydrocarbon species from the zeolite. For both hydrocarbons, CO co-feed led to a decreased oxidation light-off temperature, and therefore lower desorption temperature. By pretreating the catalyst in CO and H<sub>2</sub>O at 80 °C, and even after removing CO from the feed, the enhanced oxidation light-off behavior was observed. DRIFTS characterization shows that some form of oxidized Pd was reducible to Pd<sup>0</sup> by CO at 80 °C only in the presence of H<sub>2</sub>O. Further, this reduction appears reversible by high temperature oxygen treatment. We speculate that this reduced Pd phase serves as the active site for low temperature hydrocarbon oxidation.
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