Phase segregation mechanism of NiFe ₂ O ₄ oxygen carrier in chemical looping process

Abstract

Summary NiFe2O4 presents high redox activity and good promoted application prospect in chemical looping processes. However, phase segregation caused by outward diffusion of Fe cations often lead to low cycling stability for NiFe2O4. In this study, the inherent mechanism of phase segregation for NiFe2O4 was investigated deeply. The results indicated that reduction degree exhibited significant influence on the phase segregation of NiFe2O4 in successive redox cycles. When NiFe2O4 was reduced to Ni and Fe3O4 in redox cycles, NiFe2O4 displayed stable redox activity without phase segregation. As the reduction degree reached to FeO and FeNi, a needle‐like structure with Fe enrichment was formed on the surface of the first cycled NiFe2O4. In the subsequent redox cycles with deep reduction degree, both severe phase segregation and deactivation were occurred for spent NiFe2O4 sample. It can be seen that phase segregation is the main reason for the deactivation of NiFe2O4 instead of surface sintering in redox cycles. The results of this work provide guidance for the development of NiFe2O4‐based oxygen carriers with high redox performance.

Chemical Looping Steam Methane Reforming Process Using NiFe2O4 as Oxygen Carrier for Hydrogen Production

“…Another crucial point that needs validation is the spinel phase of OC after cycles [13,14]. As is depicted in Fig.…”

Effect of Supports on the Performance of La-Modified CoFe2O4 Oxygen Carriers in Chemical Looping Hydrogen Generation from Hydrogen-Rich Syngas

“…The occurrence of phase segregation in LCF 6 T 4 not only affects the oxygen transport capacity of the entire OC but also induces a remarkable worsening of the surface morphology. Numerous studies have also demonstrated that Fe ion segregation accelerates the sintering and deactivation of OCs. ,, In contrast, the surface structure of LCF 6 Z 4 and LCF 6 YZ 4 is adequately maintained, even though they also exhibit slight particle agglomeration and sintering. However, the surface remains relatively rich in pore structure after cycling, which facilitates the maintenance of redox activity.…”

Chemical looping steam reforming of glycerol for hydrogen production over NiO–Fe2O3/Al2O3 oxygen carriers

“…From the position of the diffraction peak, a sample is a cubic form of nickel oxide (NiO). 32 The addition of nickel is capable to form a NiFe 2 O 4 , NiAl 2 O 4 (ref. 33–35 ) material with a spinel structure.…”

“…According to previous studies, the Fe-based the OCs show relatively superior performance when the Fe 2 O 3 content is 60%. 32,38 …”