Kim J.,Heesung Catalysts |
Kim E.,Heesung Catalysts |
Han J.U.,Heesung Catalysts |
Han H.S.,Heesung Catalysts |
Han H.S.,Heesung Catalysts Corperation RandD center
SAE International Journal of Fuels and Lubricants | Year: 2013
Compressed natural gas (CNG) has been regarded as an alternative fuel for current fossil fuels such as gasoline and diesel. Recently the increasing interest in shale gas is drawing more attention to CNG vehicles of which number is expected to increase. Exhaust gas from CNG engines with lean combustion contains relatively low nitrogen oxides and particulate matters compared to conventional fossil fuel based engines. However, high amount of unburned methane, which has much higher greenhouse warming potential than CO2, limits the wide use of CNG for many applications. Even though Pd-based catalysts have been popularly studied in order to convert methane, their activity and durability have not been sufficient for practical applications to aftertreatment of lean burn CNG engines and the formation of a new Pd containing. In the present study, we developed an improved Pd-based catalyst for CNG engines by introducing Pt and promoters to enhance methane oxidation activity at low temperature and long term durability. Pt was more active to oxidize paraffinic hydrocarbons that comprise ∼10% of total hydrocarbons in exhaust gas from lean burn CNG engines. Exotherm resulting from the paraffinic hydrocarbon oxidation by Pt could promote the remaining methane oxidation by Pd. Furthermore, potential causes for the deactivation of Pd-based catalyst were investigated from the various points of Pd-sintering by high temperature exposure, PdO decomposition, sulfation and coking, and the formation of new Pd containing compound. Optimal use of support material for Pd/Pt and promoters to keep Pd stable were identified as key factors for the design of more active and durable catalyst. Copyright © 2013 SAE International and Copyright © 2013 KSAE.
Kim K.,GMDAT |
Chun K.M.,Yonsei University |
Song S.,Yonsei University |
Han H.S.,Heesung Catalysts |
Gu H.,Yonsei University
SAE Technical Papers | Year: 2011
HC-SCR is more convenient when compared to urea-SCR, since for HC-SCR, diesel fuel can be used as the reductant which is already available onboard the vehicle. However, the DeNOx efficiency for HC-SCR is lower than that of urea-SCR in both low and high temperature windows. In an attempt to improve the DeNOX efficiency of HC-SCR, the effect of hydrogen were evaluated for the fresh and aged catalyst over 2wt.% Ag/Al2O3 using a Euro-4 diesel engine. In this engine bench test, diesel fuel as the reductant was injected directly into the exhaust gas stream and the hydrogen was supplied from a hydrogen bomb. The engine was operated at 2,500rpm and BMEP 4bar. The engine-out NOX was around 180ppm-200ppm. H2/NOX and HC1/NOX ratios were 5, 10, 20, and 3, 6, 9, respectively. The HC-SCR inlet exhaust gas temperatures were around 215°C, 245°C, and 275°C. The catalyst volumes used in this test were 2.5L and 5L for both fresh and aged catalysts. The DeNOX efficiency of the 5L fresh catalyst was in the range of 0-25% without hydrogen, but it increased to 14-79% when the hydrogen was added to the feed stream. The final efficiency was a function of the hydrocarbon and hydrogen concentrations in the exhaust gas mixtures and the HC-SCR inlet temperatures. The NOX conversion efficiency of the 5L aged catalyst, which had been aged thermally at 750°C for 25hrs in an electrical furnace, was in the range of 6-75% with hydrogen and 2-22% without hydrogen. In case of the 2.5L catalyst, the DeNOX efficiency was in the range of 8-35% for the fresh catalyst and 3-9% for the aged catalyst with hydrogen. In the absence of hydrogen, the NOX conversion rate was in the range of 3-8% and 3-5% for the fresh and aged catalyst, respectively. Copyright © 2011 SAE International.