Hydrogen production for fuel cells via steam reforming of dimethyl ether over commercial Cu/ZnO/Al2O3 and zeolite

Abstract

The steam reforming of dimethyl ether (DME) over physical mixture of commercial Cu/ZnO/Al2O3 and zeolite (HZSM-5 or HUSY) was extensively studied for the hydrogen production for low-temperature fuel cells. Results indicate that time-on-stream DME conversion, hydrogen yield, and selectivity of carbon-containing products were strongly dependent on the zeolites type and mixing method of the hybrid catalyst. Significantly, the powdery mixture of HUSY and Cu/ZnO/Al2O3 showed much higher and more stable DME conversion and hydrogen yield than the granular mixture with the same composition. However, when substituting HUSY with HZSM-5 (SiO2/Al2O3=38), almost the same results were obtained irrespective of the mixing methods. These quite different results were explained based mainly on the acidic properties of the zeolites in combination with the two-step reaction mechanism of the titled reaction. The effect of the types of Cu/ZnO/Al2O3 and zeolites, weight ratio of Cu/ZnO/Al2O3 to zeolite, and space velocity on the catalytic performance was quantitatively evaluated. Under optimized conditions, over 80% hydrogen yield was achieved at 100% DME conversion, indicating that commercial catalysts are able to give satisfied results. A scheme for hydrogen production for by burning some unconverted DME outside of the reactor to maintain reaction temperature was proposed and the heat balancing indicated that the steam reforming of DME is very promising to supply hydrogen for fuel cells.