Regeneration of deactivated Fe2O3/Al2O3 oxygen carrier via alkali metal doping in chemical looping combustion

In order to reduce the cost of oxygen carriers, alkali metals (K, Na) are used to dope the deactivated Fe2O3/Al2O3 oxygen carrier, thus regenerating the redox activity of the deactivated oxygen carrier. In the case of adding the same molar amount, K could rapidly regenerate the redox performance of deactivated sample. After multiple cycles, the oxygen carrying capacity of deactivated sample doped by 5% K reached the highest oxygen carrying capacity of Fe2O3/Al2O3 before deactivation. The characterization results showed that the surface alkali metal diffused to the inside of the deactivated sample in the continuous cyclic reactions, thus forming a porous structure and then improving the gas-solid reactions in chemical looping combustion. XPS results indicated that the addition of alkali metal was beneficial to increase the content of surface adsorbed oxygen or oxygen vacancies of the deactivated Fe2O3/Al2O3. It strengthened the oxidation ability of the deactivated Fe2O3/Al2O3. In addition, the effect of K content on the regeneration of the deactivated Fe2O3/Al2O3 was also studied. The results showed that the optimum amount of K was 5%. Further increasing the amount of K had no significant effect on the regeneration of the deactivated Fe2O3/Al2O3.

Automated summary

In this study, alkali metals (potassium, sodium) were used to regenerate deactivated oxygen carriers, with potassium showing rapid regeneration of redox performance and reaching optimal regeneration at a 5% doping ratio. The addition of alkali metals improved gas-solid reactions by forming a porous structure in the deactivated sample, enhancing surface adsorbed oxygen, and increasing oxidation ability. Further increases in potassium content beyond 5% did not significantly affect the regeneration of the deactivated oxygen carriers.