A combined system of dimethyl ether (DME) steam reforming and lean NOx trap catalysts to improve NOx reduction in DME engines

This paper performs a study on a combined system of DME steam reforming (SR) and lean NOx trap (LNT) in order to improve the performance of the de-NOx catalyst in DME engines. A new concept, a combined system of SR and LNT catalysts, utilizes H2 and CO generated from the DME SR catalyst as a reductant for the LNT catalyst. The Cu-based SR catalyst was prepared by the sol-gel method; further, the LNT catalyst was used a commercial catalyst. The parameters considered in this experiment included the particle size, dispersion, and amount of Cu loaded on the SR catalyst, the cell density of the substrate of the SR catalyst, and the amount of Zn as a promoter. The experiments revealed that the highest NOx conversion was obtained in the LNT catalyst when the concentration of DME was 1% and the lean/rich time was 55/8 s; however, we decided to supply 0.7% of DME and use 55/5 s of lean/rich time in the combined system of SR and LNT to overcome the problems of DME slip and fuel penalties. The system showed the best performance regarding NOx conversion in the combined system of SR and LNT that used the Cu29Zn1/r-Al2O3 catalyst with 1% of Zn as a promoter, a cell density of 600 cpsi, and a volumetric ratio of 1.3 (SR/LNT). Finally, the NOx conversion was improved by about 20% compared to the LNT catalyst used alone.