Behaviour of freeze-casting iron oxide for purifying hydrogen streams by steam-iron process

Abstract

Alternating reductions with hydrogen and oxidations with steam have been carried out on solids with improved redox capacity showing the benefits of different synthesis methods in the steam-iron process (SIP). Solids chosen were a commercial hematite, a lab-made iron oxide doped with ceria and alumina and hematite synthesized by freeze-casting technique. The first one shows a high loss of reactivity from the first cycle on while the others keep their reduction capacity along three consecutive cycles and beyond. Isothermal experiments were also performed with the best two solids. Although all of them had hematite as the starting material, they have shown significant differences in behaviour respecting the original commercial hematite depending on the chemical (inclusion of additives that account for only 2 wt% of the solid mass) or physical (macroporosity) properties. Also the effect of long lasting runs with up to 10 cycles (reduction + oxidation) have been performed at different reduction temperatures showing a slightly higher stability of the pure iron oxide pellets produced by freeze-casting versus an iron oxide with alumina and ceria selected as structural stabilizers and accelerators of the reduction/oxidation reaction.