Micro-structured string-reactor for autothermal production of hydrogen

Novel micro-structured string-reactor designed as catalytically active wires placed in parallel into a tube was developed. The small diameter of the channels (∼100 m) leads to a short radial diffusion time, a narrow residence time distribution (RTD), and a low pressure drop. This reactor was applied for the oxidative steam-reforming of methanol (OSRM) to produce hydrogen in autothermal mode for fuel cells. The heat generated during methanol oxidation at the reactor entrance is axially transferred to the reactor zone of the endothermic steam-reforming. The brass metal wires (Cu/Zn = 4/1) were used as precursors for the preparation of string-catalysts. The brass wires have high thermal conductivity (120 W/(m K)) and the chemical composition is similar to the active phase of the Cu/ZnO/Al2O3 traditional catalyst during the steam-reforming of methanol. Brass-based string catalysts are obtained by metal/aluminium alloy formation on the outer surface of wires followed by an acid treatment leaching out aluminium. This treatment leads to an increase of the specific surface area (SSA) due to the formation of porous outer layer on the wire surface. The porous outer layer has the morphology of Raney metals. The catalysts were first tested for the steam-reforming of methanol and showed high activity together with selectivities close to 100% towards hydrogen and carbon dioxide. Then, the optimized catalyst was tested during the methanol partial oxidation (POX) and during OSRM. Oxygen was observed to be totally converted via total oxidation and therefore, higher methanol conversion in the OSRM together with CO2 selectivity of 99% and H2 selectivity of 60% were obtained. © 2004 Elsevier B.V. All rights reserved.