(526c) Steam Reforming of Dimethyl Ether by Use of Catalyst Mixture of Cu/Zn Loaded Carbon Catalyst and γ–Al2O3

Dimethyl ether (DME) is one of future clean fuels, and the efficient utilization technology is desired. It is expected that hydrogen production from DME is attractive because of high equilibrium value. Therefore, we proposed a steam reforming of DME with a new and simple catalyst system combined γ-Al₂O₃ catalyst and a Cu/Zn loaded carbon catalyst. In the proposed catalyst system, the reaction proceeded via a successive two-steps mechanism: hydrolysis of DME to methanol over solid acids as alumina and zeolites, followed by steam reforming of methanol to produce H₂ and CO₂ over Cu-based catalysts. We examined the validity of the proposed concept with the catalysts just mixed physically with Cu/Zn loaded carbon catalysts and a commercial γ-Al₂O₃ catalyst [Aldrich] calcined at 700°C in air. Cu/Zn loaded carbon was prepared from an ion exchange resin [Mitsubishi Chemical] exchanged by the Cu and Zn cations through carbonization at over 500°C. Cu and Zn particles with the size of less than 10 nm were highly dispersed on the support porous carbon with large surface area. The steam reforming of DME was carried out under an atmospheric pressure using an isothermal packed-bed reactor. When only either γ-Al₂O₃ or the Cu/Zn loaded carbon was packed, no activity was obtained for DME conversion. For the mixture of both catalysts, however, the reactivity of steam reforming was remarkably improved. The highest conversion was realized when the mixing ratio of Cu/Zn loaded carbon and γ-Al₂O₃ was 2/3 by weight. This result shows the Cu/Zn loaded carbon plays only a role of methanol reforming. When the both catalysts were packed as two large layers, the conversion of DME was low. But, the DME conversion was increased with the increase in the number of layers with small volume layer, indicating that the closest packing of both active sites for DME hydrolysis and methanol steam reforming is required for DME steam reforming. DME conversion could reach 0.43 and 0.93 at the temperature of 300°C and 360°C, respectively, gas hourly space velocity (GHSV) of 7000 h^-1 and molar ratio H₂O/DME = 5. Though it is usually inevitable to form CH₄ from large portion of reacted DME at over 350°C, CH₄ selectivity was suppressed below 0.5 % in this system. In additon, the mixing of Cu/Zn loaded carbon catalyst and γ-Al₂O₃ shows lower CO yield at same DME conversion and temperature as compared with that by a Cu/Zn loaded γ-Al₂O₃Thus, it was clarified that the proposed system was effective for the DME steam reforming.