Preparation Of Supported Catalysts Based On MCM-41 Molecular Sieve And Its Application In Catalytic Hydrogenation And Nitrification

Recently,it has been the unremitting goal of catalytic chemists to synthesize efficient,stable and cheap catalysts to promote chemical reactions under mild,green and economic reaction conditions.The development trend of catalytic system is from homogeneous to heterogeneous,from noble metals to non-noble metals,and from harsh conditions to mild conditions.Quinoline hydrogenation and aromatics nitration are two important types of reactions in the chemical industry at present.Recent research focuses on how to effectively catalyze the hydrogenation of quinoline under low temperature,solvent-free and mild conditions,and the nitration of aromatics under low acidity and mild conditions.In order to achieve the above goals,the design of green and efficient catalysts is the key to solve the problem.Multi-component metal/metal oxide catalysts formed by the combination of a variety of metals or metal oxides can show excellent catalytic performance at the phase interface,wchich have been widely used in a variety of reaction systems such as quinoline hydrogenation and aromatic nitration.However,the high energy on the large specific surface of nano multi-component metal or alloy catalysts leads to their shortcomings of easy oxidation and agglomeration in the process of catalytic reaction,which limits their application in hydrogenation reaction.Meanwhile,due to its weak acidity,acid intolerance and easy agglomeration,the application of multi-component metallic oxides in aromatic nitration is also limited.In the present work,the introduction of zeolite molecular sieve with stable structure,strong thermal stability,large specific surface area and acid tolerance into multi-component metal/metal oxide catalyst is an effective way to solve the above problems of the catalyst.The constructed molecular sieve based supported catalyst can realize green and efficient quinoline hydrogenation and aromatic nitration.MCM-41 is a kind of molecular sieve with excellent performance.It has all the advantages of traditional molecular sieve.In addition,it also has regular mesoporous pipes,which is conducive to adsorption and mass transfer.Therefore,MCM-41 molecular sieve based supported multi-component metal/metal oxide catalysts were prepared with MCM-41 molecular sieve as the carrier,which were applied to quinoline hydrogenation and aromatics nitration,respectively.The specific research work is as follows:(1)The Ni@ZrO2,NiZrOx/MCM-41 and NiZrOx were prepared by ion exchange method,impregnation method and coprecipitation method.It is confirmed by various characterization that Ni@ZrO2 has a core-shell structure with metal nickel as the core and ZrO2 as the shell.NiZrOx/MCM-41 has large specific surface and pore volume because of MCM-41.The activity of three catalysts for the hydrogenation of quinoline was investigated under green and mild conditions.The activity order of the three catalysts is Ni@ZrO2>NiZrOx/MCM-41>NiZrOx,and the reusability is NiZrOx/MCM-41>NiZrOX>Ni@ZrO2.Combined with the results of catalytic activity,reusability and atomic utilization,NiZrOx/MCM-41 is the best catalyst,and the unique advantages of supported catalyst in catalytic hydrogenation are revealed.(2)FeNiCu/MCM-41 catalyst was prepared by the impregnation method.Through various characterization methods combined with the phase equilibrium diagram of iron-nickel-copper system at 500℃,it is found that when the loading amount of the prepared catalyst is 58%and Fe/Ni/Cu is 4/6/5,the metal will spontaneously form two phases of Fe-Ni alloy and Ni-Cu alloy.The reaction mechanism can be explained by the synergistic effect of the two alloys.Ni-Cu alloy can adsorb and activate H2 molecules.Then,H2 adsorbs and activates on the surface of Ni-Cu alloy and forms H*.Meanwhile,quinoline can be adsorbed by Fe3+ on the surface of Fe-Ni alloy by the coordination.Finally,H*attacks into quinoline molecules and forms tetrahydroquinoline on the surface of Fe-Ni alloy.Surprisingly,Fe4Ni6Cu5/MCM-41 catalyst can achieve 97.5%conversion and 98%tetrahydroquinoline selectivity at 50℃ under solvent-free conditions.In addition,the reusability and gram scale-up of the catalyst also verified its industrial application potential.(3)A series of CeCuCoO/MCM-41 catalysts were prepared.Through TEM,XRD and other characterization,it is found that most of the three metal oxides are in the channel of MCM-41 molecular sieve as nanowires,and a few are on the surface of MCM-41 molecular sieve as nanoparticles.The results of Pyridine infrared and NH3-TPD showed that MCM-41 exhibited obvious Lewis acidity after loading three metal oxides.Ce4Cu6Co0.5Ox/MCM-41 is applied to the nitration of acetanilide under mild conditions(acetonitrile solvent and low acidity).91.0%conversion and 91.6%selectivity of monosubstituted nitroacetanilide can be achieved at 80℃ and 2 equivalent HNO3.The acid catalysis mechanism of the reaction is proposed.MCM-41 and the supported metal oxide are taken as solid acids.Under the acid catalysis,the polarized HNO3 produces+NO2 groups,and then electrophilic substitution reaction occurs.This study shows that MCM-41 molecular sieve can improve the acidity by loading multi-component metal oxides and realize heterogeneous catalysis as solid acid.