A New Catalyzed HC Trap Technology that Enhances the Conversion of Gasoline Fuel Cold-start Emissions

Paper #:
  • 2018-01-0938

  • 2018-04-03
Passive in-line catalyzed hydrocarbon (HC) traps have been used by some manufacturers in the automotive industry to reduce regulated tailpipe emissions of Non-Methane Organic Gas (NMOG) during engine cold start conditions. However, most HC molecules produced during gasoline combustion are only weakly adsorbed via physi-sorption onto the zeolites typically used in HC traps. As a consequence, HC desorption occurs at low temperatures resulting in the use of very high platinum group metal (PGM) loadings in an effort to combust the HCs before they leave the catalyzed HC trap. In the current study a 2.0L direct-injection Ford Focus running on gasoline fuel was evaluated with full useful life aftertreatment where the underbody converter was either a three-way catalyst (TWC) or a catalyzed HC trap. A new catalyzed HC trap technology developed by Ford and Umicore demonstrated reduced tailpipe NMOG emissions of 50% over the TWC-only system without any increase in NOx emissions. Other HC traps had at best a 25% NMOG emission reduction. Parallel laboratory reactor studies were conducted in an effort to understand the improved trapping and HC combustion features of the newly developed HC trap. Increased trapping efficiency of certain aromatics (toluene) and alkenes (2M-propene) was assigned to rapid and efficient polymerization of these species due to a combination of strong Brønsted acidity, precious metal (Pd) and base Mn+ redox active metals. During the HC desorption phase, the combustion of the adsorbed HCs occurred without gas-phase oxygen due to the delayed desorption of the large HC molecules coupled with the high redox activity of the Mn+ redox active metal in the presence of steam. Besides acting as a source of oxygen during HC combustion, the ion exchanged form of the base metal also stabilized Pd against sintering during the hot, 4-mode aging process.
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