1993-11-01

Evaluation of 3-Way Catalytic Converters for the Reduction of CH 4 in the Exhaust Stream of a CNG Fueled Vehicle 931990

Natural gas vehicle's (NGV's) hydrocarbon (HC) emission is mostly methane, and it is very hard to get rid of methane using conventional Pt/Rh based three-way catalytic converter since methane(CH4) is one of the most stable hydrocarbon species. In countries where HC is regulated in non-methane hydrocarbon (NMHC), CH4 emission is not a problem, but in other countries where HC is regulated in total hydrocarbon (THC), more effort is needed to meet the HC emission level of a NGV. In addition, methane is known to be responsible for global worming, and there is a movement to regulate CH4 emission in North America.
Recent research showed that Pd/Rh based catalyst is an effective means of reducing CH4. Other research showed that the dispersion of noble metals instead of crystalization on substrate is also an effective means of reducing CH4. In this work, various catalytic converters from major catalyst manufacturers were tested over FTP 75 emission cycle using Daewoo's NGV, and hydrocarbon species were analyzed using a gas chromatography from each CVS bags (cold transient, stabilized, and hot transient phases). Daewoo's NGV already showed that its emission level is lower than its parents gasoline vehicle using conventional Pt/Rh based three-way catalytic converter.
Within the scope of this work, it is found that Pd is an effective catalyst for removing CH4, and Pt/Pd/Rh catalyst is found to perform better than Pd/Rh catalyst in removing CH4 under fuel-lean condition.

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