Hydrogen production via partial oxidation and reforming of dimethyl ether

The catalytic partial oxidation and reforming of dimethyl ether (DME) over composite catalysts composed of 6 wt%Ni/Al2O3 and noble metal supported on Al2O3 were investigated for the production of hydrogen under ambient pressure. Results indicate that Rh/Al2O3 had better performance than Pt/Al2O3 for the titled reaction. The modification of Rh/Al2O3 with different contents of alkali metal nitrates, i.e., LiNO3, NaNO3, and KNO3, was comparatively studied. The N2 adsorption/desorption results showed that both the surface area and pore volume of the Rh/Al2O3 obviously decreased with the increase of the content of the modifiers. Moreover, the pore size distribution of Rh/Al2O3 was significantly changed by the addition of LiNO3. Irrespective of the modifiers, there were no diffractions assigned to Rh by XRD analysis. By the addition of less than 5 wt% Na into Rh/Al2O3, hydrogen yield was obviously increased while DME conversion was always 100%. When the content of Li in Rh/Al2O3 was less than 5 wt%, the effect of modifier on both DME conversion and hydrogen yield was negligible. However, the stability of the catalyst indicated either by DME conversion or by hydrogen yield was apparently decreased when the content of Na or Li in Rh/Al2O3 was greater than 5 wt%. Even at a lower content of 2.5 wt%, the addition of KNO3 into Rh/Al2O3 deteriorated the stability of the catalyst although there was basically no effect on the initial hydrogen yield and DME conversion. Based on the characterization results and the possible reaction networks, these experimental phenomena were tentatively explained as the electronic promotional effect of alkali metal nitrates on Rh and the structural effects of the modifiers on the pore properties of the catalyst.