The influence of metals and acidic oxide species on the steam reforming of dimethyl ether (DME)

The performance of catalysts from the platinum group and Cu-based catalysts were compared in the dimethyl ether (DME) steam reforming reaction.Without acidic oxides, Cu-based catalysts formed undesired CH4 via a direct decomposition of DME into methoxy (–OCH3) and methyl (–CH3) groups, followed by the hydrogenation of the methyl group to CH4. However, in the presence of acidic oxides such as Al2O3, practically no CH4 was produced. Therefore we speculate that the MeOH formed on the acidic sites moves onto Cu and is adsorbed as a methoxy group without the co-formation of a methyl group, preventing the formation of CH4 and leading to an even higher yield of H2.Pt/Al2O3 and Ru/Al2O3 showed a relatively high DME conversion, although the undesired production of CH4 was quite high, irrespective of the presence of acidic sites. A high CH4 selectivity can be explained in terms of a high methanation activity.The catalyst formed from CuMn2O4 spinel oxide mixed with Al2O3 showed higher activity and greater durability than commercial CuZnAl catalysts mixed with Al2O3. By replacing Al2O3 with H-ZSM5, the CuMn2O4 spinel oxide showed a further increase in activity resulting in up to 100% conversion even under 300 °C. We attribute this very high activity at relatively low temperature to both the high DME hydration activity of H-ZSM5 and the high MeOH steam reforming activity of CuMn2O4 spinel oxide.

Graphical abstractA comparative study of various Cu-based catalysts was performed on the steam reforming reaction of dimethyl ether (DME). Ru/Al2O3 showed very high CH4 production, irrespective of the presence of acidic sites, due to the high intrinsic methanation activity of Ru metal. In contrast, Cu-based catalysts did not produce CH4 as a by-product when mixed with acidic oxides such as Al2O3. CuMn-spinel + Al2O3 was superior to commercial CuZnAl + Al2O3, exhibiting higher DME conversion at a lower temperature. Replacing Al2O3 with a zeolite led to a further increase in activity. The higher performance of the CuMn-spinel catalyst can be attributed to its high methanol steam reforming activity. Thus, the activity and selectivity of this process strongly depend on the identity of the metals and acidic oxide species employed.Figure optionsDownload full-size imageDownload as PowerPoint slide