Isomorphous replacement in Fe2O3–NiO/Al2O3 particles and its effect on oxygen carrier performance.

Using Fe 2 O 3 , Fe 2 O 3 /Al 2 O 3 , and Fe 2 O 3 –NiO/Al 2 O 3 as oxygen carriers (OCs) on chemical looping combustion with CO was investigated in this study. All the modified iron-based OCs were prepared by sol–gel method, and the samples were characterized by X-ray diffraction (XRD), N 2 adsorption/desorption, and scanning electron microscope/energy dispersive X-ray spectroscopy. The temperature-programmed reduction showed that loading on Al 2 O 3 will promote the reduction of Fe 2 O 3 to Fe 3 O 4 , but further reduction will be inhibited, and the addition of NiO can effectively reduce this inhibition. Thermogravimetric analysis also revealed that NiO addition can improve the maximum reaction rate of iron-based OCs in the oxidation stage. Mixing with NiO will also decrease the oxygen capacity of iron-based OCs. The XRD data of the reduced samples showed that both Al 2 O 3 and NiO have an isomorphous replacement effect on Fe 3 O 4 . The isomorphous replacement effect of NiO is much stronger than that of Al 2 O 3 . Thus, NiO introduction can effectively inhibit the formation of FeAl 2 O 4 and promote the further reduction of Fe-oxides to Fe. However, Ni 2 + will replace part of the Fe 2 + in Fe 3 O 4 to form NiFe 2 O 4 and slightly decrease the oxygen capacity of iron-based OCs. [ABSTRACT FROM AUTHOR]