Hydrogen production from dimethyl ether over Cu/γ-Al2O3 catalyst with zeolites and its effects in the lean NOx trap performance

The purpose of this study is to investigate the effects of mixing three kinds of zeolites (MFI, MOR, and BEA) with the dimethyl ether steam reforming(DME-SR) Cu/γ-Al2O3 catalyst to improve H2 yield at low temperatures, and to identify the de-NOx performance of a combined system of SR catalyst and Lean NOx Trap(LNT). The SR catalyst was prepared by the impregnation method, and a commercialized LNT catalyst was used. The SR reaction experiment was conducted to investigate the effect of the coexistence of CO2, O2, NO, and NO2 among the exhaust gases of the DME engine on the H2 yield. The study found that the proper mixing of Cu/γ-Al2O3 and zeolite increased the H2 yield at low temperature improving DME hydrolysis. The variation in the H2 yield according to the kinds of zeolite in the SR catalyst was due to the characteristics of zeolite. The Cu10/γ-Al2O3 catalyst mixed with 10% MOR showed the highest H2 yield. A combined system of SR and LNT uses the H2 generated mainly from the Cu-based catalyst using the DME-SR reaction for the LNT. When H2 generated from the SR (Cu10/γ-Al2O3 + MOR10) catalyst was used as the reductant of LNT, the NOx conversion at 350 °C or below was improved up to 15% compared to when DME was used. This demonstrates that H2 as the reductant of LNT is more beneficial than DME. The H2 generated from the SR catalyst can be used as the reductant of LNT in an after-treatment system. Meanwhile, the SR catalyst that was mixed with zeolite caused the carbon deposition, but the combined system of SR + LNT caused no carbon deposition because the carbon deposited on the SR catalyst reacted with O2 during the lean-operating period.

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► SR catalyst of Cu10/γ-Al2O3 + MOR(mordenite)10 yielded the highest H2 generation rate of 55% at 300 °C.
► The existence of CO2, NOx and O2 in the exhaust gases decreased H2 yield from the SR reaction.
► When H2 as the reductant of LNT was used, NOx conversion of the combined system of SR+LNT was 15% higher at 350° C than that of LNT.