De-NOx Performance of Combined System of Reforming Catalyst and LNT for a DME Engine

Dimethyl ether(DME) is easily reformed into H₂, since the chemical structure of DME does not feature direct C-C bonds, in contrast to diesel fuel. We have researched reforming catalysts for effectively generating H₂ from the exhaust gases of a DME engine. The objective of this study is to evaluate the de-NOx performance of a combined system of RC(Reforming Catalyst) and LNT(Lean NOx Trap) for a DME engine according to reforming catalysts. The H₂ generation of the reforming catalyst was observed under various conditions. CAT-A, CAT-B and CAT-C were prepared as reforming catalysts, and OC(Oxidation Catalyst) and LNT (Lean NOx Trap) were examined as commercial catalysts. The CAT-A catalyst has a higher amount of acid sites compared to the CAT-B and CAT-C catalysts. The CAT-A which is a mixing of mordenite and γ-Al₂O₃, has the highest H₂ yield. However, the H₂ yield decreased in the reforming reaction when CO₂, NO and O₂ coexisted. The NOx conversions of the combined system of fresh and hydrothermally aged CAT-A+LNT are higher by about 8% and 6% than those of the LNT. The NOx conversion over the combined system of CAT-A+LNT applied to the DME engine has been improved at high rpm-load conditions compared to the LNT.