Preparation And Catalytic Performance Of Ruthenium-based Metal (Alloy) Catalyst Materials With Confined Structure

Ru-based nano metal catalysts are used in the hydrogenation of aromatic compounds and the oxidation of small molecules,for example,the semihydrogenation of DMT,the oxidation of ethyl acetate,the oxidation of CO,etc.,all show excellent catalytic activity.In order to solve the aggregation phenomenon of precious metal catalysts,a large number of scientific researchers are involved in the development of novel structures.At present,catalysts with finite field effects have attracted attention in this regard,because they have the function of enhancing the stability of metal ions,adjusting their electronic effects with the environment,and improving the activity of catalytic reactions.Hydrotalcite is a good carrier and catalyst precursor material with a restricted structure.It is inevitable to use its own advantages(laminate cation exchangeability and restricted effect)to develop new catalytic materials.In this research paper,the two-way confinement effect of the interlayer and the layer of hydrotalcite is used to prepare the RuMgAl-LDHs(prepared by the urea method)catalyst precursor into a highly dispersed and confined to water after controlled reduction in an H2 atmosphere.Supported Ru-based nanoparticle catalyst with edge structure of talc layer,Ru/MgAl-LDH.Furthermore,the MgCuAlRu-LDHs quaternary hydrotalcite was prepared by the double-drop constant pH method as the catalyst precursor,and the nanoalloy catalyst RuCu/MgAlOx was obtained after treatment in the H2 environment.A variety of characterization methods were used to analyze the preparation process and reaction mechanism of the above two materials.The effect of the addition of Cu on the reduction process of Ru is studied and discussed.Finally,the two catalysts Ru/MgAl-LDH and RuCu/MgAlOx are put into the corresponding reaction:benzene hydrogenation;carbon monoxide preferential oxidation(CO-PROX).Test the activity,selectivity and stability of the catalyst,and build the structure and performance.Main experimental content and results:(1)Use the urea method to exchange Ru ions into the hydrotalcite laminate to form a highly crystalline RuMgAl-LDHs catalyst precursor material.The supported Ru nanoparticle catalyst is prepared by controlling the calcination reduction temperature under a hydrogen atmosphere to prepare a supported Ru nanoparticle catalyst limited to the edge of the hydrotalcite layer.Using XRD,HRTEM,STEM-EDS and other characterization methods,it is found that with the increase of reduction temperature,Ru particles gradually migrate to the edge area of hydrotalcite,forming Ru/MgAl-LDH with restricted structure.It is worth noting that when the reduction temperature reaches 80?,hydrotalcite will produce a "secondary state" phenomenon.The main reason is that Ru is reduced and grown into nanoparticles,which changes the interlayer spacing of hydrotalcite.Until 110?,almost all of the Ru particles migrate to the edge of the hydrotalcite laminate and disappear.The Ru/MgAl-LDH prepared at different treatment temperatures is used in the catalytic hydrogenation of benzene.Under the reaction conditions of 90 ? and 5 MPa H2,the catalyst obtained by the reduction treatment at 100? has the highest conversion rate and stability the best.The excellent catalytic performance mainly controls the reduction temperature and combines the hydrotalcite laminates and the confinement between the layers to form a highly dispersed supported Ru-based catalyst at the edge of the hydrotalcite confinement.(2)MgCuAlRu-LDHs with flower cluster-like morphology and high crystallinity were prepared by the double drop method as the catalyst precursor.After high-temperature calcination and reduction in a hydrogen atmosphere,a highly dispersed hexagonal shape with a confined structure in MgAlOx was obtained.Domain RuCu alloy catalyst,namely RuCu/MgAlOx.Research and analysis using characterization techniques such as XPS,HRTEM,HAADFSTEM,Ir-Drifts,etc.,show that the Ru and Cu bimetals will produce the following different states during the reduction process:At 450?,Ru is preferentially reduced and forms particles.Loaded on CuOx;at 550?,CuOx is reduced to Cu by the hydrogen overflow on the surface of Ru particles,and forms RuCu alloy with Ru;at 650?,Cu is affected by high temperature and releases the RuCu alloy,resulting in the crystallization of Ru particles Grid distortion.The catalysts of different structures are used in the CO-PROX reaction.The results show that the restricted RuCu/MgAlOx catalyst treated at 550? has high selectivity and 100%CO conversion ability in the reaction temperature range,and the catalyst has high stability,long catalytic life,and is not affected by space velocity.Features.The excellent performance benefits from the special properties of the hydrotalcite laminate-atomic-level dispersion of metal ions and lattice confinement,which makes it extremely difficult to form molten two metals to interact to form an alloy during the preparation process.In the process of catalytic reaction,Cu changed the adsorption site and reaction pathway of Ru for CO,and promoted the improvement of performance.