Preparation And Application Of Carbonized Chitosan Microspheres Supported Nano-palladium Catalysts

Chitosan is a biomass resource derived from natural biopolymer chitin （mainly from seafood waste such as crab shell and shrimp shell）.Because of its biocompatibility,good biodegradability,and rich amine and hydroxyl active groups,it is widely regarded as the ideal raw material for the synthesis of various functional nanomaterials in biomedicine,photoelectric energy storage,catalysis,and other fields.Especially in the field of catalysis,the presence of abundant N/O groups in chitosan can induce strong interaction between the chitosan skeleton and nano-metal,thus promoting the anchoring of nano-metal particles.In addition,due to the inherent rigidity of the chitosan molecular chain,chitosan in nature is mostly multi-layer micro and nano structure.This multi-layer porous structure is conducive to the adhesion and dispersion of nano-metals,which makes the active metal sites more easily dispersed,and also promotes the diffusion of reaction solvent/substance.Quinoline and its derivatives are widely used in the fields of organic synthesis,coordination chemistry,and drug synthesis,and its selective hydrogenated products have many applications in medicine,pharmacology,and engineering.Reducing amine synthesis to secondary amine is an important reaction in the synthesis of drugs,petrochemical products,and polymers on an industrial scale.Therefore,it is of great research value to develop a low-cost,green,and efficient catalyst for the synthesis of the amine compounds mentioned above.Combined with previous studies,a series of porous nitrogen-doped chitosan nanospheres supported Pd nanocatalysts（Pd/CNCM）were successfully prepared in this paper,which were successfully used in the catalytic reaction of selective hydrogenation of quinoline and its derivatives and reduction amine synthesis into secondary amine.In order to further expand the application field of the catalyst and solve the problem of water pollution caused by dyes in today’s society,Pd/CNCM was used in the dye degradation reaction and showed good degradation effect.Specific research contents are as follows:（1）Chitosan was used as raw material to prepare 3D porous chitosan nanospheres（CNM）using sol-gel method.To further improve the surface properties of CNM microspheres and enhance their application in the field of catalysis,3D porous nitrogen-doped chitosan nanospheres（CNCM）were further carbonized（at 800℃）.Pd（OAc）₂ was used as the precursor of Pd species,CNCM was used as the support to obtain Pd²⁺/CNCM by the impregnation method,and the Pd/CNCM catalyst was obtained by reduction with NaBH₄.The prepared Pd/CNCM catalyst has a nanoporous structure and abundant N/O functional groups.The characterization results show that Pd NPs have good dispersion over CNCM,narrow particle size distribution,and no local aggregation,with an average particle size of 2.28nm.Pd/CNCM catalyst was used in selective hydrogenation of quinoline and its derivatives.The catalyst showed excellent catalytic performance and good substrate applicability.（2）Using Pd/CNCM as catalyst and NaBH₄ as initiator,the degradation effects of the catalyst were investigated on various dyes,including corundum red（CR）,methylene blue（MB）,methyl orange（MO）,Rhodamine B（Rh B）,phenol red（PR）and methyl red（MR）were investigated.When the catalyst dosage was 2 mg,the degradation rate was85.3%-93.4%.Compared to commercial Pd/C,Nano-Pd,unloaded chitosan microspheres,NaBH₄and other catalytic systems,Pd/CNCM has the best dye degradation and reduction performance.The degradation rate of Pd/CNCM can still reach 82.1%to 90%after 7 cycles,and the catalytic activity does not decrease significantly,indicating that the Pd/CNCM catalytic system has good stability and recyclability.（3）To explore the effect of the carbonization temperature on the surface properties of the microspheres and the catalyst activity,CNM was carbonized at different temperatures（250,500,750,1000℃）,and a series of porous N-doped chitosan nano-carbon microspheres supported palladium catalysts（Pd@CNCM-T℃）was prepared.Characterization analysis showed that Pd nanoparticles were evenly distributed on CNCM,with an average diameter of 2.29～9.74 nm.When the carbonization temperature is 750℃,the metal particle size distribution is narrow and the dispersion is good.Secondary amines were prepared by the"one-pot"reduction amination reaction of amines and aldehydes catalyzed at Pd@CNCM-750℃.Compared with commercial catalysts for Pd/C,Nano-Pd,and Pd（OAc）₂ catalysts,the catalysts showed excellent catalytic activity and cycle stability（～5 times,89%）and a wide range of substrate applicability（33 substrates）.