Effect of Diverse Hydrocarbons on the Cold Start Behavior of Three-Way Catalysts

A new experimental setup is introduced, enabling a preheated exhaust gas mixture to abruptly heat up an initially cold monolith catalyst and, thus, reproduce transient catalyst light-off behavior. With this setup, cold start experiments have been carried out on an aged monolithic Pd three-way catalyst (TWC). This study aims at systematically investigating the effect of diverse hydrocarbons, including methane, acetylene, ethene, ethanol, acetaldehyde, propane, propene, toluene, and xylene in TWC exhaust. It was shown that the commonly used model components propane and propene do not represent the behavior of aromatics and other hydrocarbons present in a typical TWC exhaust very well, since they do not account for their variability in inhibition strength and reactivity. Among the studied hydrocarbons, acetylene proved to be the strongest inhibitor; even at low concentrations of 70 ppm (a typical value found in TWC exhaust), acetylene inhibition increases CO cold-start emissions by 40 %. Furthermore, aromatic and liquid hydrocarbon species (like ethanol) first condense on the initially cold catalyst surface and evaporate again as the catalyst heats up, resulting in a desorption peak at the catalyst outlet.