Study the structure stability of NiFe2–xCrxO4 (x = 0, 0.08) during H2/CO2 cycle reaction

H2/CO2 cycle reaction activities of spinel structure NiFe2–xCrxO4 (x = 0, 0.08) prepared by co-precipitation were determined. The results showed that pure NiFe2O4 had almost lost its CO2 decomposition activities after 15 cycles, while Cr3+ doped NiFe2O4 still had about 40% of the initial reaction activity value after 50 reaction cycles. The magnetic properties of samples annealed at 350 C indicated that Ms and Mr decreased from 32.49 to 26.04 emu/g and 9.39 to 7.31 emu/g, respectively, but Hc increased from 230 to 1800 Oe with the increasing of Cr3+content. XRD Rietveld analysis showed that there appeared 23.15% FeyNi1–y (0 < y < 1) and no Fe3C in pure NiFe2O4 system after the first H2/CO2 cycle reaction. With the increasing of cycle times, the phase abundance of NiFe2O4 decreased rapidly. At the same time, Fe3C appeared and its content increased fast. After 15 cycles, the phase abundance of NiFe2O4 is less than 5%wt, but those of FeyNi1–y (0 < y < 1) and Fe3C enhanced to 48.15 %wt and 46.92 %wt, respectively. However, the cycle reaction life of NiFe2–xCrxO4 (x = 0.08) was much longer than NiFe2O4. The spinel structure stability was improved dramatically because of the existing of Cr3+ in the cell of NiFe2O4. After 50 cycles, the phase abundance of NiFe2O4 still had 20 %wt.