Hydrogen is considered as a clean source of energy and steam reforming of dimethyl ether (DME) is regarded as a promising method to produce hydrogen for fuel cell applications. Unlike many other fuels (e.g. methanol methane and bio-ethanol), DME is non-toxic and provides high H/C ratio and high energy density. Generally, steam reforming of dimethyl ether (DME SR) (Eq. (1)) consists of two moderate endothermic reactions: DME hydrolysis (Eq. (2)) to methanol over a solid acid catalyst, followed by steam reforming of methanol (MSR, Eq. (3)) over a steam reforming catalyst. Therefore, a bi-functional catalyst consisting of acid sites and MSR sites is required for overall DME SR process.
DME steam reforming: CH3OCH3 + 3H2O → 6H2 + 2CO2 △Hr = +135kJ/mol (1)
DME hydrolysis: CH3OCH3 + H2O → 2CH3OH △Hr = +37kJ/mol (2)
MeOH steam reforming: CH3OH + H2O → 3H2 + CO2 △Hr = +49kJ/mol (3)
For DME hydrolysis system, a novel plate-type anodic γ-Al2O3 as monolithic support was prepared through the anodization technology, and its catalytic performance for hydrolysis of dimethyl ether (DME) was compared with that of the commercial γ-Al2O3. The results show that the anodic Al2O3/Al monolith exhibited higher catalytic activity than the commercial γ-Al2O3 due to its stronger acidity, better hydrophilicity and lower activation energy. Moreover, a 120h stability evolution was carried out and the results show that the plate-type anodic alumina has an excellent ability for coke suppression, which demonstrated that the novel anodic γ-Al2O3/Al monolith was an excellent acidic catalyst and support for DME SR.
For DME SR system, a series of Cu/γ-Al2O3/Al bi-functional catalysts were prepared by impregnation method. The catalytic performance of Cu/γ-Al2O3/Al catalysts both with and without H2 pre-reduction was compared. It was found that these two composite catalysts exhibited the similar catalytic activity. Meanwhile, according to XRD and XPS results, copper species over un-reduced catalyst was reduced to metallic Cu after DME SR reaction, indicating the in situ reduction of CuO in the reaction condition of DME SR. However, Cu-based catalysts have poor thermal stability and can easily lose catalytic activity due to the sintering of metallic Cu above 300°C. To improve the thermal stability of Cu, several components (e.g. Mn, Cr, Ni) were added to the Cu-based catalyst and their catalytic performance for DME SR was studied. It was found that Ni-doped catalyst had excellent catalytic activity. Moreover, the durability test of Cu/Ni/γ-Al2O3/Al was carried out under critical conditions (400°C) and the results show that it has an excellent stability for 100h with a 100% DME conversion, which demonstrated that the novel plate anodic γ-Al2O3/Al monolith supported Cu and Ni composite catalyst was an excellent catalyst for DME SR. Furthermore, it would be very promising for the application of micro-channel reformer for the domestic fuel cell system as for its outstanding shape flexibility and catalytic performance.