Preparation And Catalytic Performance Of Supported Nano-Pd Catalysts From Small Tree Leaves

Precious metal nanomaterials have the unique properties of both precious metals and nanomaterials,and are widely used in the field of catalysis.The heterogeneous palladium nano-catalysts as C-C coupling catalysts have shown great potential in catalyzing Suzuki coupling reactions because of their high catalytic efficiency and easy recovery.The preparation of heterogeneous catalysts with high catalytic activity often requires the addition of chemical reducing agents and stabilizers,which will cause environmental pollution.The development of a green and efficient heterogeneous nano-palladium catalyst has become a major problem faced by current chemical researchers.In this paper,the supported palladium catalysts and palladium-copper alloy catalysts were synthesized by a one-pot method using the leaves of Cloves,Acer L and Ficus carica Linn.as raw materialswithout chemical stabilizers and reducing agents.The prepared catalysts were analyzed and characterized by XRD,UV-Vis,FT-IR,SEM,TEM and XPS etc.The Suzuki coupling reaction was used as a probe reaction to investigate the catalytic performance of the catalysts.Using Clove leaf extract as reducing agent and stabilizer,Clove fiber as carrier,and Na₂PdCl₄ as precursor,a supported palladium catalyst(Pd/RCL-b)was synthesized.The effect of biological and chemical methods on catalyst properties and catalytic performance was studied.The viewpoint that the polyphenols,polysaccharides and flavonoids in clove leaves can effectively reduce Pd²⁺and stabilize PdNPs through complexation during the preparation process,thereby preparing PdNPs with smaller particle size and higher activity Pdcatalyst has been proved by experimental results.The PdNPs in the catalyst prepared by one-pot biological reduction have a face-centered cubic structure,with(111)crystal planes as the main component,and an average particle size of 4.49 nm.It is used to catalyze the Suzuki coupling reaction of 4-bromonitrobenzene and phenylboronic acid.At 60�C,with the addition of 0.05 mol%of the catalyst,the biphenyl yield can reach 96.22%at 20 min,which is higher than the catalyst prepared by chemical methodand commercial Pd/C.Using Acer L leaf extract as reducing agent and stabilizer,Acer L leaf fiber as carrier,and Na₂PdCl₄ as precursor,a supported palladium catalyst(Pd/RAS)was synthesized in one-pot method.The effect of loading on the properties and catalytic performance of the catalysts was investigated.With the increase of the catalyst loading,the particle size of PdNPs in the prepared catalyst gradually increases,and the catalytic activity of the catalyst gradually decreases.When the loading is too low,the catalytic effect is reduced due to the carrier adsorbing the substrate of the catalytic reaction.The results of the experiment found that the main reducing and stabilizing substances in the leaves were tannins,flavonoids,and polyphenols.When the catalyst loading is 3 wt%,the catalyst has the best catalytic effect.In this case,the PdNPs with an average particle size of 3.08 nm in the synthesized catalyst exhibit a face-centered cubic structure,mainly with(111)crystal faces.To catalyze the Suzuki coupling reaction of 4-bromonitrobenzene and phenylboronic acid as the substrate,add 0.06 mol%of the catalyst at 40�C,and react for30 min.The yield of biphenyl can reach 97.72%.A supported palladium copper catalyst(PdCu/RFL)was synthesized by one-pot method using Ficus carica Linn.leaf extract as reducing agent and stabilizer,Ficus carica Linn.leaf fiber as carrier,Cu SO₄ and Na₂PdCl₄ as copper and palladium sources respectively.The influence of the ratio of palladium to copper on the properties and performance of the catalyst was investigated.The spherical PdCu NPs with an average particle size of 3.94 nm and a lattice spacing of 0.218 nm in the nanoparticles was successfully prepared by the abundant coumarins,flavonoids,tannins,vitamin C and amino acids in Ficus carica Linn.leaves as reducing agents and stabilizers.The lattice spacing of PdCu NPs proved that an alloy is formed between palladium and copper.This alloying effect not only greatly reduces the cost of the catalyst but also helps to improve the catalytic activity and stability of the catalyst.Experiments show that when the ratio of palladium to copper is 4:1,the catalyst achieves the highest catalytic activity and stability.It is used in the Suzuki coupling reaction of 4-bromonitrobenzene and phenylboronic acid as the substrate,and 0.06 mol%of the catalyst is added to the reaction system,reacting at 60�C for 30 min,the yield of biphenyl can reach 97.00%.The experimental results showed that the bio-supported palladium nanocatalyst was successfully synthesized by the one-pot method.Using this method not only simplifies the preparation process of the supported palladium catalyst,but also can effectively stabilize PdNPs through the oxygen-containing and nitrogen-containing groups in the reaction system,which is beneficial to the synthesis of small particle size PdNPs,thereby improving the catalytic performance and stability of the catalyst.This method provides a simple,efficient and green way for the preparation of supported nano-palladium catalyst.