Catalytic Performance Of Bio-Co/Cu-MOFs Derived Catalysts For Reductive-amination Tandem Reaction

Amines and imines are regarded as versatile chemical intermediates for the the synthesis of various agrochemicals,pharmaceuticals,dyes,polymers and resins.Among various synthetic methods of imines and amines,the one-pot reductive amination of nitroarenes with carbonyl compounds has attracted significant attention because of the availability of raw materials,limited byproducts,low pollution and high atomic efficiency.However,it remains a significant challenge to develop a high-efficiency catalyst that can realize controllable synthesis of imine and amine through the tandem reaction due to over-hydrogenation of imines into amines.Among various catalysts for the tandem reaction,metal-organic frameworks(MOFs)derived porous materials possess much more stable than pristine MOFs,and inherit the advantages of MOFs including high porosity,large surface area and tailored structure,which expands its application.In this paper,three Bio-MOFs derived catalysts were fabricated through employing Bio-MOFs materials as precursors from the viewpoint of realizing controllable synthesis of imine and amine through the one-pot reductive amination of nitroarenes with aromatic aldehydes.Then,these Bio-MOFs derived catalysts were applied for reductive amination tandem reaction.The structure-activity relationship of Bio-MOFs derived catalyst and the interior mechanism of tandem catalysis were deeply studied.The detail research contents listed as following:(1)A Cu/Zn bimetallic Bio-MOFs(Cu Zn-MOFs)were synthesized by one-pot solvothermal method utilizing adenine,4,4'-biphenyl dicarboxylic acid,zinc acetate dehydrate and copper acetate monohydrate.Furthermore,a Zn O/nitrogen-doped carbon composite supported Cu catalyst(named as Cu-Zn O/NC-BMOFs)was prepared via Cu Zn-MOFs as self-sacrificing template.The developed Cu-Zn O/NC-BMOFs catalyst was applied for the tandem reaction towards reductive amination of nitrobenzene with benzaldehyde.The bimetallic Cu Zn-MOFs with the uniformly dispersed Cu and Zn centers acted as a self-sacrificing template,which could facilitate the derived catalyst with strengthened Cu-Zn O interaction,high dispersity,as well as high concentration of N species.These advantages endow the developed Cu-Zn O/NC-BMOFs catalyst with higher catalytic activity and selectivity in one-pot reductive amination of nitrobenzene with benzaldehyde compared with the traditional Cu/Zn O/NC-IWI(prepared by incipient wetness impregnation)catalyst.More importantly,the Cu-Zn O/NC-BMOFs catalyst could convert nitroarenes into the corresponding imines or secondary amines with excellent selectivity(>90.0%)by adjusting different reaction temperature(130 ^oC and 200 ^oC).(2)Based on the synthesis of Cu Zn-MOFs material,a Co/Zn bimetallic Bio-MOFs(Co Zn-MOFs)were synthesized via one-pot solvothermal method using adenine,4,4'-biphenyl dicarboxylic acid,zinc acetate dehydrate and cobalt acetate tetrahydrate.A novel Co₃Zn C and Zn O supported on N-doped carbon nanosheet catalyst with the thickness of ca.5.0 nm was fabricated through the direct pyrolysis of the bimetallic Co Zn-MOFs at 500 ^oC(named as Co₃Zn C-Zn O/NC-500).Surprisingly,the developed Co₃Zn C-Zn O/NC-500 catalyst delivers 99.9%conversion of nitrobenzene and 98.5%selectivity to N-benzylideneaniline in one-pot reductive amination of nitrobenzene with benzaldehyde.Various characterizations(including as SEM,XRD,TEM,AFM,XPS,Raman and N₂ adsorption-desorption)have revealed that the generated small size of Co₃Zn C alloy,abundant structural defects,larger specific surface area(105.5 m²·g^-1)as well as more basic sites are responsible for the outstanding catalytic activity of Co₃Zn C-Zn O/NC-500 catalyst for tandem reaction.Moreover,the Co₃Zn C-Zn O/NC-500 catalyst exhibits high stability during the recycling experiments without the loss of its catalytic activity.Notably,the results of contrast experiments have demonstrated that the intentional introduction of Zn O in Co₃Zn C-Zn O/NC-500catalyst plays a key role in the selectivity to N-benzylideneaniline in the tandem reaction.Thus,a Zn O support-assisted strategy(changing the Zn O support of the catalyst to achieve controllable synthesis of imines and/or amines)was developed to further improve the selectivity to imine in the tandem reaction.(3)Based on the synthesis of Co Zn-MOFs material,a phosphomolybdic acid encapsulated in bimetallic Co Zn-MOFs(PMo@Co Zn-MOFs)composite were obtained by one-pot solvothermal method applying phosphomolybdic acid as Mo source.Two novel nitrogen doped cobalt molybdenum carbide(Co-Mo-C-N)and phosphorus doped cobalt molybdenum carbide(Co-Mo-C-P)were synthesized by the direct pyrolysis of PMo@Co Zn-MOFs composite with different Co/Zn molar ratio.The developed Co-Mo-C-N and Co-Mo-C-P catalysts were applied for the tandem reaction towards reductive amination of nitrobenzene with benzaldehyde.Co-Mo-C-N catalyst exhibits the outstanding selectivity of imine(99.9%),while Co-Mo-C-P catalyst delivers the excellent selectivity of secondary amine(99.9%)at 99.9%conversion of nitrobenzene.Density functional theory(DFT)demonstrate that the imine adsorption energy and activation energy of imine hydrogenation of Co-Mo-C-P is lower in comparison with Co-Mo-C-N,which is favorable for the hydrogenation of imine to form secondary amine.Thus,an active species-assisted strategy(adjusting to achieve controllable synthesis of imines and/or amines)was further developed on the basis of the Zn O support-assisted strategy for controllable synthesis of products.In this paper,from the viewpoint of tuning reaction temperature,support and heteroatom doping of catalyst,the catalytic reaction mechanism for reductive-amination tandem reaction of nitroarenes was investigated.This study provides a new guideline for solving the problem of of how to control products selectivity in tandem catalysis.