The Research For The Catalytic Hydrogenation Of Carbon Dioxide With Spinel Ferrite

Spinel ferrites are important kind magnetic materials, used as magnetic recording materials, microwave absorbers and other functional materials in practical applications, and they have well future in catalysis, biology and other fields. Because of the increasing global warming, people are looking for effective ways to fix the main component of greenhouse gas CO2, such as the CO2 decomposition to carbon or low-carbon organic hydrogenation. The oxygen vacancy formed by spinel ferrite (MFe2O4) reduced partially has a high CO2 hydrogenation methanation activity and is useful to achieve CO2 conversion.In this thesis, we prepared NiFe2O4, CoFe2O4, Co1-xZnxFe2O4 and NiFe2O4-ZrO2 aerogels with the integrity crystal structure, good magnetic properties, large surface area and good dispersion by the ethanol-water heating and supercritical fluid drying. Then we used the NiFe2O4 and NiFe2O4-ZrO2 as catalysts for CO2 methanation. The main contents include the following:1. The ferrites and their composites aerogels were formed by the precursor prepared via the ethanol-water heating followed supercritical fluid drying (SCFD) technology. In the preparation of CoFe2O4 ferrite, we found the best pH of wet chemical processes was 7.5; For Co1-xZnxFe2O4 ferrite, the saturation magnetization decreases, the specific surface area gradually increased and the grain size decreases slightly with the Zn content increasing; For NiFe2O4 ferrite, the grain size decreases and the surface area increases with the increasing reaction temperature in the preparation of the wet chemical process. NiFe2O4 ferrite was used in catalytic hydrogenation of CO2 methanation, CO2 conversion rate increased with the increasing temperature in wet chemical processes; the catalyst with screening mesh for the 40-60 and content for 1g has the highest CO2 conversion and the methane selectivity was 100%. 2. The comparison studies of CO2 hydrogenation methanation with NiFe2O4-ZrO2 catalyst samples by different methods of the ethanol-water heating followed supercritical fluid drying or calcination at a certain temperature, the common precipitation method followed calcination at different temperatures show that the sample prepared via ethanol-water heating followed supercritical fluid drying has a highest conversion of CO2 and the 100% methane selectivity; and the samples via ethanol-water heating followed calcination at a certain temperature and common precipitation followed calcination at different temperatures have lower catalytic activity.3. The NiFe2O4-ZrO2 samples prepared via ethanol-water heating followed supercritical fluid drying show their catalytic activity decreases gradually with increasing of reaction temperature or decreasing of NiFe2O4 content in samples. The studies on the stability of ferrite catalysts show that the NiFe2O4-ZrO2 compared with NiFe2O4 has better reaction stability of the spinel structure due to the presence of ZrO2, and the spinel structure has not changed before and after the reaction. The CO2 conversion rate and methane selectivity remained at 62.86% and 100% respectively after 200h continuos reaction.