Screening of NiFe2O4 Nanoparticles as Oxygen Carrier in Chemical Looping Hydrogen Production

The objective of this paper is to systematically investigate the influences of different preparation methods on the properties of NiFe2O4 nanoparticles as oxygen carrier in chemical looping hydrogen production (CLH). The solid state (SS), coprecipitation (CP), hydrothermal (HT), and sol-gel (SG) methods were used to prepare NiFe2O4 oxygen carriers. Samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) surface area measurement, as well as Barrett-Joyner-Halenda (BJH) porosity test. The performance of the prepared materials was first evaluated in a TGA reactor through a CO reduction and subsequent steam oxidation process. Then a complete redox process was conducted in a fixed-bed reactor, where the NiFe2O4 oxygen carrier was first reduced by simulated biomass pyrolysis gas (24% H-2 + 24% CO + 12% CO2 + N-2 balance), then reacted with steam to produce H-2, and finally fully oxidized by air. The NiFe2O4 oxygen carrier prepared by the sol gel method showed the best capacity for hydrogen production and the highest recovery degree of lattice oxygen, in agreement with the characterization results. Furthermore, compared to individual nickel ferrite particles, the mixture of NiFe2O4 and SiO2 presented remarkably higher stability during 20 cycles in the fixed-bed reactor. The structural and morphological stability of samples after reactions was also examined by XRD, XPS, and SEM analyses.