Steam reforming of dimethyl ether over ZSM-5 coupled with Cu/ZnO/Al₂O₃ catalyst prepared by homogeneous precipitation

Steam reforming of dimethyl ether (DME) was carried out over combined solid acid/Cu-based catalysts. The reaction proceeded via a successive two-steps mechanism: hydrolysis of DME to methanol over solid acids, followed by steam reforming of methanol to produce H₂ and CO₂ over Cu-based catalysts. Effective hydrolysis catalysts were zeolites, among which ZSM-5 showed the highest activity as well as selectivity to methanol. When ZSM-5 was combined with Cu-based catalysts, a high yield of H₂ production was obtained with Cu/ZnO/Al₂O₃ catalyst prepared by homogeneous precipitation (hp-) by urea hydrolysis. Moreover, the highest activity was obtained, when powders of both hp-Cu/ZnO/Al₂O₃ and ZSM-5 were kneaded in an agate mortar, pressed and sieved to the particles of composite catalysts. Either physical mixing of the particles of both catalysts or separate filling of ZSM-5 and hp-Cu/ZnO/Al₂O₃ resulted in the low activity, indicating that the closest packing of both active sites for DME hydrolysis and methanol steam reforming is required for DME steam reforming. As a Cu-catalyst in the composite catalysts, hp-Cu/ZnO/Al₂O₃ showed higher activity than hp-Cu/ZnO and moreover than that prepared by coprecipitation. It is likely that hp-preparation affords more finely dispersed Cu metal particles and moreover Al component stabilizes the finely dispersed Cu metal particles on the catalysts against sintering. The catalyst deactivation due to coke formation is discussed in connection with the analytical results of coke materials.