Preparation Of Nano-palladium By Reduction Of Plant Extracts And Its Catalytic Properties

The supported nano-palladium catalysts were prepared by biological reduction method using Poplar leaves and Pine needles extract as the reducing agent,stabilizing agent,Na2PdCl4 as the precursor,the corresponding residue and magnalium hydrotalcite as the carrier,respectively.The structure and morphology of the as-prepared palladium nanoparticles(Pd-NPs)were characterized by FT-IR,XRD,XPS,TEM,and SEM.The catalytic performance of the as-prepared catalysts were examined by the Suzuki coupling reactions.The Pd/RPL catalyst,with 5 wt%Pd loads(Pdo.os/RPL),was prepared by biosynthetic method using Poplar leaves extract(PLE)as the reducing agent and the extracted residue of Poplar(RPL)as the carrier.The results of characterization demonstrated that the spherical Pd-NPs are evenly dispersed on the RPL surface.The above-prepared supported Pd-NPs are mainly for Pd(111)Bragg reflections of the face centred cubic(fcc)structure.The Pd-NPs have a narrow size distribution of 1.66 nm-5.46 nm and a mean particle size of about 3.12 nm.And the reductive degree is 70%.FT-IR analysis can speculate that water-soluble heterocyclic compounds,with-OH groups,e.g.tannins,terpineol,flavonoids,polyphenols,act as reducing agent in the reaction process.And the protein compounds,with(NH)-C=O groups,can serve as a stabilizing agent.The yield of 4-bromotoluene with phenylboronic acid catalyzed by Pdo.os/RPL reached 98.29%in the presence of 1‰ catalyst for substrate at 60? for 30 min.After five repeated cycles,the yield can remain more than 81%.The Pd/RPN catalyst,with 3 wt%Pd loads(Pd0.03/RPN),was prepared by biosynthetic method using Pine needles extract(PNE)as the reducing agent,Pine needles extract residue(RPN)as the carrier.The results of characterization demonstrated that the spherical Pd-NPs are evenly dispersed on the RPN surface.The above-prepared supported Pd-NPs are mainly for Pd(111)Bragg reflections of the face centred cubic(fee)structure.The Pd-NPs have a narrow size distribution of 1.52 nm-5.26 nm and an average diameter of 3.25 nm.And the reductive degree is 68%.FT-IR analysis can speculate that water-soluble heterocyclic compounds,with-OH groups,e.g.terpineol,flavonoids,polyphenols,act as reducing agent in the reaction process.And the protein compounds,with(NH)-C=O groups,can serve as a stabilizing agent.The yield of 4-bromotoluene with phenylboronic acid catalyzed by Pd0.03/RPN reached 98.56%in the presence of 1‰ catalyst for substrate at 60? for 30 min.A yield of 84%is still obtained in the sixth cycle.The Pd/LDHs catalysts,with 3 wt%Pd loads(Pd0.03/LDHs-PLE and Pd0.03/LDHs-PNE),were prepared by employing magnalium hydrotalcite(LDHs)as the carrier,PLE and PNE as the reducing agent,respectively.The results of characterization demonstrated that the spherical Pd-NPs are evenly dispersed on the LDHs surface.The Pd-NPs have an average particle diameter size of 2.29 nm and 1.75 nm,respectively.And the reductive degree is 67%and 71%,respectively.For the Suzuki coupling reaction of 4-bromotoluene with phenylboronic in the presence of 0.5‰ catalyst for substrate at 60? for 30 min,the yield can reach to 98.89%and 99.01%,respectively.After the eighth recycled reaction,the yield of two kinds of catalysts can be above 95%.The results showed that the plant extract(PLE and PNE)can serve as the reducing agent in the reduction of Pd2+ to Pd0,effectively.Compared with Pd/RPL and Pd/RPN,the Pd/LDHs catalyst has smaller particles size,excellent catalytic activity and recyclability in the Suzuki coupling reactions.