Hydrogenation Of CO₂to Hydrocarbons Over Iron Nanoparticles Confined In Nanoporous Carbons

With the rapid economic development in many countries around the globe, the emission of carbon dioxide has been rapidly increasing. The emission not only leads to the greenhouse effect, but also causes a huge waste of carbon resources. Making effective use of CO2has become an important issue all over the world. It is becoming a hot area in CO2utilization to transform CO2into value-added light hydrocarbons.A series of catalysts confining iron nanoparticles in ordered mesoporous carbons were prepared through a solvent-evaporation induced self-assembly (EISA) method. Under the pressure of3MPa, the reaction temperature of673K, a space velocity of1800mL h-1g-1(cat) and the molar ratio of H2/CO2=3, the catalysts for hydrogenation of carbon dioxide were investigated in a fixed bed down-flow reactor.1. The impact of iron nanoparticle size on catalytic activity was investigated. Using F127as a template, phenolic resol as a carbon source and iron nirtrate as a metal source, the size of iron nanoparticles was readily tunable by adjusting acetylacetone amount. With the increase of acetylacetone content (from0to0.27g), the nanoparticle size became smaller and the catalytic performance was better. When0.27g acetylacetone was added during the synthesis, CO2conversion could reach56.4%and the selectivity of C2+reached49.3%.2. Fe(acac)3contents impact on activity was investigated at the1073K carbonization temperature. The catalyst with0.4g Fe(acac)3showed better catalytic performance and higher selectivity towards C2+. With carbonization temperature increasing, graphitization degree was enhanced, the nanoparticles size was increased, and the selectivity towads C2+was decreased. When the carbonization temperature was673K, the conversion of CO2was52.8%, the selectivity of C2-C4=could reach19.5%and C2+selectivity reached56.8%. As the carbonization temperature rose to973K, CH4selectivity increased from26.1%to38.5%, C2-C4=selectivity decreased to1.1%and the selectivity towards C2+also decreased to48.3%.3. Fe(acac)3, Fe(NO3)3and FeCl3precursors were used and the resulting activity of the catalyst was determined. The catalyst synthesized with Fe(acac)3precursor showed the best catalytic performance, next was the catalyst synthesized with Fe(NO3)3precursor, while catalyst synthesized with FeO3precursor was not active for hydrogenation of carbon dioxide to hydrocarbons. 4. Promoters were added to modify catalytic performance. Moderate amounts of K promote the selectivity of C2-C4to reach as high as29.8%, possibly because K could modulate the competitive adsorptive capacities of H and C species. Cu promoter also improves the reducibility and dispersity of the Fe catalyst with C2+selectivity reaching63.3%. Zr and Ce promoters enhanced CO2hydrogenation, but the selectivity of C2-C4=decreased to some extent and C2-C4alkane selectivity increased.