Studies On Catalysts For Hydrogen Production From Low Temperature Steam Reforming Of Dimethyl Ether

Facing energy crisis and the deterioration of the environment, hydrogen has shown a good momentum of development because of its renewability, high efficiency and non-pollution. It is becoming a hot topic in the scope of fuel cell. Due to its features of higher hydrogen content, stability, non-toxicity, safe storage and transportation, Dimethyl Ether (DME) is regarded as an ideal hydrogen carrier. Hydrogen production from steam reforming of DME is one of the important directions in fuel cell research area because of its low reaction temperature, less by products and high efficiency.In this paper, catalysts and some processing conditions for dimethyl ether steam reforming were studied. Firstly, the activities of solid acids were investigated for DME hydrolysis, and the optimum hydrolysis catalyst was determined. Then a series of PdZn/ZrO₂ and CuPdZn/ZrO₂ catalysts were prepared for DME steam reforming by deposition precipitation, impregnation and coprecipitation. Structures of catalysts were characterized by means of nitrogen adsorption and XRD. The steam reforming of dimethyl ether was carried out in a continuous fixed-bed reactor with the mechanical mixture of hydrolysis catalysts and reforming catalysts. The effects of calcination temperature, surfactants, loading sequence of active component, loading methods of active component and amount of Cu were discussed. Thus, the optimum composite catalysts were obtained. Finally, some processing conditions such as reaction temperature, reduction temperature and GHSV were explored.Studies showed that: PdZn/ZrO₂ catalysts prepared by deposition precipitation method show better performance on DME steam reforming. The suitable preparation conditions of composite catalysts are as follows: adding surfactant into Zr(OH)4 hydrosol, calcination temperature 500℃for carrier ZrO₂, mechanical mixing Pd/Zn-loaded ZrO₂ with hydrolysis catalyst. Catalysts prepared under such conditions demonstrate high activity and excellent selectivity in the DME reforming reaction. The yield of the H2 can reach 56.1%, the total yield of CO and CO₂ can be over 19.8%, CO₂ selectivity is 90.1%. The addition of Cu into PdZn/ZrO₂ catalysts displays no obvious improvement in reforming reaction. The results of processing conditions showed that when the reaction temperature was at 300℃, reduction temperature was at 400℃, GHSV was 8400 mL·h-1·g-1cat, the mass ratio of hydrolysis and reforming catalyst was 1:1, the performance of the catalyst was better in the DME steam reforming reaction.