Design,synthesis And Catalytic Performance Of Iron-based Nanocatalysts

The catalyst can change the path of the chemical reaction,speed up the reaction rate,and will not be consumed in the reaction.Among the existing catalyst systems,heterogeneous catalysts are widely used in industrial production and catalysis due to their specific characteristics.In recent years,heterogeneous catalysts have received more and more attention from researchers,and the development of efficient,stable and low-cost catalysts has become a major concern.Electrocatalytic carbon dioxide reduction is a promising environmental protection strategy,which can not only reduce the emission of greenhouse gas carbon dioxide,but also convert carbon dioxide into a series of value-added chemical products,which has received much attention in recent years.In the process of carbon dioxide reduction,the inertia of carbon dioxide is the major challenge in the process.On the other hand,inhibition of competitive hydrogen evolution reaction(HER)is another challenge in this reaction.Hydroreduction of nitroaromatic hydrocarbons is an important industrial reaction for the production of aromatic amines,which are important intermediates of dyes,pharmaceuticals and pesticides.It is a great challenge to achieve high selectivity in this process.Due to the complex hydrogenation mechanism of nitroaromatic hydrocarbons,the selectivity of amines will be reduced through the generation of byproducts such as hydroxylamine,azo and azo oxides.In addition,reducible functional groups(such as unsaturated bonds)can undergo competitive hydrogenation,further reducing the selectivity of amine products.In this paper,three kinds of iron-based nanomaterials were designed using ZIF-8 as the precursor,and their applications in electrocatalytic reduction of carbon dioxide and hydrogenation reduction of nitroaromatic hydrocarbons were studied.The main research contents are as follows:(1)The blue powders containing Cu and Fe were prepared by adding copper phthalocyanine and iron nitrate during the synthesis of ZIF-8.Nitrogen coordination Cu-Fe bimetallic site catalysts were prepared by pyrolysis of the samples in a tube furnace at 1000°C.The Cu-Fe-N₆-C catalyst exhibited high CO Faraday efficiency(98%at-0.7 V)during the electrocatalytic reduction of CO₂to CO.The initial selectivity and CO Faraday efficiency were maintained after 10 hours of continuous electrolysis.The experimental results and theoretical calculations show that the synergistic catalysis of different metal sites increases the adsorption enthalpy of CO₂and decreases the activation energy,resulting in high selectivity,high stability and low impedance.This work not only provides a new way to reduce CO₂emissions and convert CO₂into valuable products,but also provides a new idea for the design and synthesis of bimetallic active site catalysts.(2)ZIF-8 modified with ammonium ferric citrate was synthesized by stirring ammonium ferric citrate,zinc nitrate and 2-methylimidazole in methanol.The sample was pyrolyzed in a tube furnace at 900°C to prepare nitrogen-doped porous carbon catalysts with Fe single atom and Fe₂O₃clusters highly dispersed.The catalyst has excellent catalytic performance and high selectivity in the hydrogenation reduction of nitroaromatic hydrocarbons.Nitrobenzene can be completely converted to aniline at room temperature of 0.2 h,and the selectivity can reach more than 99%.The catalyst has excellent catalytic performance and high selectivity for the conversion of various nitro compounds to aromatic amines.The catalyst can still maintain high catalytic activity after being recycled for 6 times.In this work,a novel porous carbon catalyst with single metal site and cluster dispersion was designed,which provides a new approach for the efficient hydrogenation reduction of nitroaromatic hydrocarbons.(3)ZIF-8 was ultrasonically dispersed in n-hexane,and Fe Cl₃aqueous solution was added,and Fe³⁺was introduced into the channel of ZIF-8 by double solvent approach.Fe/Fe₃C supported by nitrogen doped carbon nanotubes were prepared by pyrolysis of the synthesized samples in a tubular furnace at 900°C.The catalyst can completely convert nitrobenzene to aniline at 40°C for 0.8 h with a selectivity of 99%.The catalyst also has excellent catalytic performance and high selectivity for the conversion of various nitro compounds to aromatic amines.The excellent catalytic performance is attributed to the fact that carbon nanotubes can greatly reduce the leaching degree and prevent the aggregation of metal particles.The catalyst can still maintain high catalytic activity after repeated use for 5 times.This work provides a new approach for the design and construction of metal/metal carbide supported nitrogen-doped carbon nanotubes.