Insights into the relationship between microstructural evolution and deactivation of Al2O3 supported Fe2O3 oxygen carrier in chemical looping combustion

The Fe2O3-Al2O3 oxygen carrier is regarded to a promising candidate for chemical looping combustion (CLC). However, Fe2O3-Al2O3 oxygen carrier was often subjected to a decrease of oxygen carrying capacity. The deactivation mechanism of Fe2O3-Al2O3 oxygen carrier in chemical looping combustion was investigated over consecutive 20 cycles. The Fe2O3-Al2O3 oxygen carrier exhibited relatively poor redox stability in a fixed bed reactor. The physico-chemical properties of cycled Fe2O3-Al2O3 oxygen carrier were characterized by different characterization methods. No carbon deposit was detected in the reduction process, indicating that carbon deposition was not the cause for Fe2O3-Al2O3 oxygen carrier deactivation under this experimental condition. The characterization results showed that the deactivation of Fe2O3-Al2O3 oxygen carrier in redox cycles was mainly attributed to thermal sintering. The cycled Fe2O3-Al2O3 oxygen carrier showed lower surface area, lower reducibility and oxygen mobility than that of fresh sample. After a certain number of redox cycles, Fe diffusion and enrichment at the surface of cycled oxygen carrier was observed. The surface Fe is unstable under high reaction temperature, leading to accelerate thermal sintering. A deactivation mechanism of Fe2O3-Al2O3 oxygen carrier in CLC was proposed based on the Fe diffusion and surface sintering.