Research On Nickel-based Single-atom Catalysts For The Reduction Of Amination Reactions On Biomass

In the 21st century,decreasing fossil energy reserves and environmental pollution are the main problems facing mankind,and the development of renewable energy sources has become the focus of attention.Biomass is the only renewable carbon resource in nature and has the potential to partially replace fossil resources in the production of fuels and chemicals.Through chemical transformation,biomass can produce a range of compounds containing aldehyde and ketone groups,including furfural,levulinic acid and its esters,benzaldehyde and its derivatives,and so on.These compounds can be used to prepare a variety of nitrogen-containing chemicals by reductive amination reactions,which are widely used in pharmaceuticals,dyestuffs,polymer synthesis and other fields.For reductive amination reactions,homogeneous catalytic systems mostly suffer from high cost and difficulty in recovery,while non-homogeneous catalytic systems are recoverable but conventional metal nanocatalysts generally suffer from a series of problems such as low efficiency,harsh reaction conditions and poor stability.Based on this,nickel-based single-atom supported catalysts（Ni₁@NC）were prepared in this thesis,and the basic properties such as structural characteristics,surface properties,and electronic valence states of the catalysts were studied through a series of test characterization methods.By optimizing the reaction conditions,the synthesis of primary amines and pyrrolidones by reductive amination of biomass-based aldehydes and levulinate compounds was achieved,respectively.The specific research contents are as follows:First,Ni₁@NC,a nickel-based single-atom loaded catalyst,was prepared by a strategy of pyrolysis polymer re-reduction.It was structurally characterized by XRD,SEM,TEM,AC-HAADF-STEM,XPS,TGA,etc.It was demonstrated that the Ni metal was atomically distributed on the catalyst carrier,mainly immobilized by the pyridine nitrogen and pyrrole nitrogen structures in the carrier,and that the valence state of Ni was between 0 and 2 valence.In addition,single-atom loaded catalysts Ru@NC and Co@NC were prepared using the same method for ruthenium-based and cobalt-based catalysts,respectively.Secondly,the single-atom Ni₁@NC catalyst and other related catalysts were applied to study the reductive amination reaction of aldehyde、s and ketones at room temperature,and the test results showed that Ni₁@NC had the best effect among the prepared catalysts.Under the reaction conditions of 2 mol/L ammonia-methanol solution,1 MPa H₂,and 24 h,the model substance benzaldehyde could be efficiently converted at room temperature to obtain 96%yield of the target product of benzylamine.Applying this method to other all-pass compounds with different structures and functional groups,including aromatic aldehydes and ketones with various substituents,aliphatic aldehydes and aliphatic ketones,biomass-based furfural and 5-methylfurfural,the target products were obtained in 80%～99%yields.Mechanistic studies showed that the Ni-N_x site in the structure of the single-atom Ni₁@NC catalyst activated hydrogen by a hindered Lewis acid-base pair（FLP）mechanism.Finally,the catalyst showed good stability in the recycling experiments,and the activity remained essentially unchanged in five recycling reactions species.Finally,single-atom Ni₁@NC was used to catalyze the reductive amination of ethyl levulinate and aniline to prepare N-phenylpyrrolidone at room temperature.The research results showed that the highest 90%N-phenyl-5-methylpyrrolidone compound was obtained under the reaction time of 1 MPa H₂ and 24 h with methanol as the solvent.The system is applied to the conversion reaction of aniline derivatives with different substituents,including aniline compounds with electron-donating and electron-withdrawing groups,and alkylamines with different structures,and 75%～86%of the target product can be obtained.Rate.Finally,the stability of the catalyst in this reaction was investigated,and the activity remained basically unchanged during 5 cycles of recycling.