Preparation-dependent oxygen release and apparent carbon deposition of Cu–Fe/ZrO2 oxygen carriers during wheat straw chemical looping conversion

Cu–Fe/ZrO 2 composite oxygen carriers with identical nominal compositions were prepared by mechanical mixing (MM), impregnation (IM), and sol–gel synthesis (SG) to investigate how preparation route affects oxygen release, cyclic stability, gas-product distribution, and apparent carbon deposition during wheat straw chemical looping conversion. Oxygen-release behavior was evaluated by thermogravimetric cycling at 900 °C under N 2 with air regeneration at 700 °C, and the carriers were characterized by XRD, SEM, and N 2 physisorption before and after cycling. Fixed-bed tests were subsequently conducted with wheat straw to quantify gas yields, gas-phase carbon conversion, and apparent carbon deposition. SG exhibited the lowest onset oxygen-release temperature (741.5 °C) and the highest apparent oxygen-release capacity (3.38 wt%). After 20 release–reoxidation cycles, its capacity remained 3.35 wt%, corresponding to 99.11% retention. In the first fixed-bed cycle, SG achieved a gas-phase carbon conversion of 79.17%, with CO 2 and CH 4 yields of 24.70 and 0.75 mmol g −1 , respectively. After 20 cycles, its gas-phase carbon conversion remained 78.71%, while apparent carbon deposition was 1.84 mg g −1 , 63.8% lower than that of MM. In contrast, in the first fixed-bed cycle, IM produced the highest H 2 and syngas yields among the three carriers, reaching 7.56 and 13.71 mmol g −1 , respectively. These results demonstrate that preparation route governs the balance between oxygen availability, cyclic stability, carbon accumulation, and syngas preservation in Cu–Fe/ZrO 2 oxygen carriers.