Effects of Hydrocarbon Structure on Adsorption Energetics on BEA Zeolite

Calvin  Thomas, Oak Ridge National Laboratory

Despite continual advances in the field of low temperature oxidation catalysts, cold-start emissions of hydrocarbons remain a significant challenge for automotive vehicles. Hydrocarbon traps have proven to be a promising technology for lessening these emissions. They work by adsorbing hydrocarbons at low temperatures, when the catalyst is inactive for hydrocarbon oxidation, and releasing them at higher temperatures, once the catalyst becomes active. These traps are zeolite based, usually SSZ-13, ZSM-5, or BEA, and often they are ion exchanged with Pd or Ag. Previous work has shown that these traps can be effective for mitigating the impact of cold-start emissions. However, work to date has not examined the effect of different functional groups on the storage behavior of the hydrocarbon traps.

In this work, the isothermal storage behavior of different hydrocarbons on a model BEA zeolite hydrocarbon trap is investigated. The hydrocarbons used are ethanol, m-xylene, 1-octene, iso-octane, and n-octane. These hydrocarbons represent some of the most prevalent types of hydrocarbons in gasoline while maintaining a constant carbon number of 8 with the exception of ethanol, which is included because of its prevalence in gasoline and exhaust. This allows us to determine the energetics of adsorption and how those energetics change based on hydrocarbon structure. These insights will be invaluable for future modelling efforts on hydrocarbon traps.