Investigation Of Iron-Based Catalysts For C₅+Hydrocarbons Synthesis From CO₂Hydrogenation

Utilization of CO2as a feedstock for producing chemicals not only contributes to alleviating global climate changes caused by CO2emissions, but also provides a challenge in exploring environmental friendly fossil fuels. This work focused in the process of CO2hydrogenation to hydrocarbons over iron-based catalyst. The main results are shown as follows:1. Fe-K/Al2O3catalysts with increasing Fe content showed more active sites, while increasing K content inhibited H2adsorption and increased the ratio of olefin/paraffin. Catalyst activity was influenced by the structure of metal precursor. The catalyst calcined at400℃performed the best.2. Both CO2conversion and hydrocarbons selectivity increased when reduction temperature increased to some extent. Catalyst activity was improved by increasing molecular ratio of H2/CO2or reaction pressure, as well as decreasing space velocity. However, increasing reaction temperature resulted in the decrease of long-chain hydrocarbons selectivity.3. SiO2coating not only improved the hydrophobicity of Fe-K/Al2O3catalysts, but also decreased reduction temperature of iron oxides. By restrain the competitive adsorption of H2O, the chemisorption and activation of reactants was improved. The catalyst with9wt%SiO2coating showed both high CO2conversion (63%) and high selectivity toward C2+hydrocarbons (74%), while further higher coating led to suppression of catalyst activity.4. CO2conversion and C5+selectivity were influenced by the composition, pore structure and surface physico-chemical properties of support materials. For Al2O3support, basic hydroxyls favored the dispersion of iron particles and the adsorption of intermediated product CO. Iron-based catalyst supported on Al2O3with more basicity exhibited high catalyst activity and C5+selectivity. Ferric nitrate and K2O destroyed the structure of zeolite support to some extent, differed from the framework type. SiO2generated during catalyst preparation and CO2hydrogenation resulted in the increase of CO selectivity, while the generation of Al2O3favored the adsorption of CO2, both CO2conversion and C5+selectivity increased.5. Particle size, morphology and crystal phase of FexOy played an important role in CO2hydrogenation. Catalyst performed better with decreasing particle size, due to the enhancement of reduction behavior. Among all hematite samples, spindle performed the best, while cubic a-Fe2O3showed the lowest CO2conversion. Using magnetite as iron source instead of hematite could increase reduction degree of the catalyst, C5+selectivity increased obviously. Sphere formed by agglomeration of small particles performed better than hollow sphere Fe3O4...