Preparation Of Hollow Microspheres Supported Palladium Nanoparticles By Self-Stabilized Precipitation Polymerization

The loading of Pd nanoparticles(Pd NPs)on support materials is the key to preventing their agglomeration and realize the high activity and excellent stability of Pd nanocatalytic system.Hollow polymer microspheres(HPPs)were prepared by self-stabilized precipitation polymerization method developed in our laboratory and applied to the loading of Pd NPs.The effects of surface modification of HPPs and different reduction methods reduction of Pd2+ on the structure and performance of the prepared catalysts were investigated in detail.The main contents and achievements of this thesis are as follows:1.Cross-linked hollow Poly(divinylbenzene-alt-maleic anhydride)particles(HPPs)were prepared by a template method using self-stabilized precipitation polymerization.The HPPs were uniform in size with an average particle size of 0.51 ?m and a shell thickness of 100 nm.HPPs-SH and HPPs-NH2 were prepared by surface modification of HPPs with 2aminoethanethiol and diethylenetriamine.The morphology of the HPPs after modification was well maintained,and the average size was slightly larger(0.57 um for HPPs-SH and 0.58 um for HPPs-NH2).2.Pd@HPPs,Pd@HPPs-SH and Pd@HPPs-NH2 catalysts were prepared by ethanol insitu reduction method and methanol-mediated reduction method.Studies have shown that the ethanol in-situ reduction method can load Pd NPs on the surface of the HPPs more effectively.The Pd NPs on the surface of Pd@HPPs were uniformly distributed and exist in the form of face-centered cubic crystals(fcc)with an average particle size of 12.6 nm(Carrier/Pd=20,mass ratio).The relative proportions of Pd(0)and Pd(II)on the surface of different types of carriers were analyzed,results showing that the proportion of Pd(0)on the carrier surface varied in the order:HPPs>HPPs-NH2>HPPs-SH.The effect of the carrier/Pd mass ratio on the activity of the catalyst was studied,and the results showed that the catalyst prepared when the carrier/Pd=20(mass ratio)has higher catalytic activity.The optimized Pd@HPPs(EtOH)catalyst at this stage catalyzes the reduction of p-nitrophenol at room temperature under the conditions of 2 mL H20,1 mL NaBH4(0.1 M),30 ?L 4-NP(0.01 M),and 30 ?L catalyst(10 mg/mL).The apparent reaction rate constant kapp=1.67×10-2s-1 in the reaction.3.The reduction method of Pd2+ of the catalyst was changed to to yield finer Pd NPs.Using NaBH4 as reducing agent,under the conditions of 25%ethanol as the solvent,HPPs/Pd=20(mass ratio),and 1 mM NaBH4,Pd@HPPs(NaBH4)catalyst with HPPs as the carrier was prepared.The Pd NPs on the surface of the HPPs had a particle size of 8.8 nm and a Pd content of 2.04 wt%.The catalyst had excellent catalytic performance.The apparent reaction rate constant kapp=1.85×10-2 s-1,and the normalized rate constant k'=0.97 s-1 mM-1.The stability tests showed that the catalyst maintained high catalytic activity after 8 times of continuous catalysis.Preliminary research on the ability of Pd@HPPs(NaBH4)catalyst to catalyze Suzuki coupling reaction.The results showed that under the conditions of Iodobenzene(0.5 mmol)with Phenylboronic acid(0.75 mmol),in presence of 0.01 g Pd@HPPs(NaBH4)(0.2%Pd),1 mmol K2CO3 or KOH as a base and 5 mL ethanol as a solvent,at 80? for 4 h.The yield of target product Biphenyl is over 99%.