Stabilizing effect of support materials on iron-based oxygen carrier pellets for chemical looping hydrogen in long-term operation

This work investigates the impact of iron-based oxygen carriers (OCs) on green hydrogen production using a fixed-bed chemical looping (CL) process, aiming for industrial scalability. We conducted a comprehensive material screening of OCs comprising Fe₂O₃ with support materials (Al₂O₃, TiO₂, ZrO₂) at an 80/20 wt.-% ratio. Focus was placed on ZrO₂, pure and doped with CaO, MgO, and Y₂O₃, to examine their effects on redox efficiency and hydrogen production. Notably, ZrO₂ doped with MgO and Y₂O₃ achieved a specific hydrogen production over 12 molH₂/kgOC at a small scale, attributed to chemical inertness and porous morphology, enhancing cyclic stability over traditional TiO₂ and Al₂O₃ supports. Large-scale testing of the most promising OC compositions in a 250 g fixed-bed reactor for 100 cycles revealed that doping ZrO₂ with Y₂O₃ not only prevents phase transitions but also ensures higher cyclic stability among tested OCs. Our findings underscore the critical role of microscopic phenomena in the CL process's efficiency and introduce a novel approach for designing environmentally friendly OCs for effective hydrogen production.