NiO/NiAl2O4 oxygen carriers prepared by sol-gel for chemical-looping combustion fueled by gas

Chemical-looping combustion with inherent CO2 enrichment depends on the high-powered oxygen carriers. Ni(NO3)2 and Al(OC3H7)3 are selected as the main raw materials to prepare sol-gel-derived NiO/NiAl2O4, by matching the appropriate experimental parameters. The oxygen carrier with a mass content of 60% NiO, a sintering temperature of 1300°C, and a sintering time of 6 h performs comparatively good physicochemical properties. The circular reduction–oxidation reaction between NiO/NiAl2O4 and methane/air has been investigated with the help of a thermogravimetric analyzer (TGA). X-ray diffraction (XRD), scanning electron microscope (SEM), and the N2 adsorption–desorption (BET) methods were utilized to characterize the physicochemical properties of the fresh and used oxygen carriers. The experimental results show that the sol-gel-derived NiO/NiAl2O4 oxygen carriers demonstrate an extremely good recycling ability of reduction–oxidation reaction. The reduction of NiO occurs in the presence of CH4, and the reduced Ni is oxidized to NiO in air. As the circulation proceeds, the reduction degree is gradually intensified and the oxidation degree is gradually alleviated. The rates of the reduction intensification and the oxidation alleviation decrease gradually, and then the reduction–oxidation reactivity of the oxygen carriers increases by degrees. The sintering behavior between different particles is not observed, and the porous beehive structure of the particle is maintained after several circle reduction–oxidation reactions. These experimental results prove that the sol-gel-derived oxygen carrier NiO/NiAl2O4 is capable of being equipped by chemical-looping combustion fueled by CH4.