Evolution of redox reactivity and mechanical strength of disc-granulated CaMn0.375Ti0.5Fe0.125O3-δ perovskite oxygen carriers during chemical looping combustion

Abstract

Mechanical strength decay and attrition of oxygen carriers during long-term redox cycling remain key obstacles to the industrialization of chemical looping combustion (CLC). In this work, spherical CaMn 0.375 Ti 0.5 Fe 0.125 O 3-δ perovskite oxygen carrier particles (400–800 μm) were synthesized via a scalable disc granulation method using low-cost Ca(OH) 2 , Mn 3 O 4 , TiO 2 , and Fe 3 O 4 raw materials, and their long-term cyclic performance was evaluated in a micro fluidized bed thermogravimetric analyzer (MFB-TGA). The fresh particles exhibited a mechanical strength above 35 N (∼87 MPa), far exceeding that of natural ores (0.5–6.8 N). Although the specific surface area dropped below 0.1 m 2 /g at a calcination temperature of 1350 °C, the reactivity remained essentially unaffected owing to rapid lattice‑oxygen transfer, with an oxygen transport capacity of ∼6 wt%. After 60 deep redox cycles, the crushing strength decayed sharply to 0.2–1.2 N (0.5–3 MPa) due to severe fragmentation and powdering. In contrast, after 60 controlled redox cycles (oxygen transport capacity limited to ∼2.5 wt%), the strength remained at 12–18 N (24–50 MPa), with a minimum attrition rate of ∼0.05 wt%·h −1 . Particles calcined at 1400 °C for 12 h further survived 1000 controlled redox cycles without deactivation, agglomeration, or sintering, retaining an average crushing strength of ∼14 N (∼47 MPa) — only ∼22% decay in crushing strength and ∼ 4.7% in compressive strength. Post-cycle XRD and SEM/EDS analyses confirmed a stable perovskite phase and uniform elemental distribution, demonstrating that controlling the redox depth suppresses particle fragmentation, enhances redox kinetics, and reduces attrition. These findings provide a practical route toward durable, highly active oxygen carriers for industrial CLC demonstration.