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.