Synthesis of Catalytic Systems Based on Nanocomposites Containing Palladium and Hydroxycarbonate
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2012年l0月 第 3卷增刊1 贵金属
Precious Metals 0ct.2012
V_01.33.No.s1
Synthesis of C atalytic Systems Based on Nanocomposites Containing Palladium and Hydr0xycarb0nates of Rare—Earth Elements
GALANTSEVA M.V ,.,BUSLAEVA M. ,PAKKANEN T ,FOMICHEV V V ,MISCHIHINA E.A. (1.Moscow State University ofFine Chemical Technologies named after M.V Lomonosov(MITHT named after M.V Lomonosov), Moscow,Russia;2.University of Eastern Finland(UEF),Joensuu,Finland.)
Abstract:The purpose of this work is to synthesize the catalytic systems containing palladium nanoparticles and using hydroxycarbonates of yttrium and cerium as supports,and to test the catalytic activity of the obtained catalysts in the Suzuki CROSS—coupling reaction.Nanocomposites Pd/Y(OH)CO3 and Pd/Ce(OH)CO3 were synthesized according to two methods:the first one—simultaneous production of nanoscale substrate and immobilization of palladium nanoparticles on its surface(nanocomposites 1),the second one—the prior synthesis of polyvinylpyrrolidone stabilized palladium nanoparticles followed by their immobilization on the nano—sized substrate surface(nanocomposites 21.The reaction between phenylboronic acid and iodobenzene is chosen as a model one.The dependence of the catalytic activity of catalysts on the method of their synthesis was established. It was established that nanocomposites 2 exhibit higher catalytic activity in the selected reaction compared to the nanocomposites 1.The TOF values fur the nanocomposites 1 are 6663-14617 h一 when using the substrate Ce(OH)CO3 and 1 3774-27084 lr when using the substrate Y(OH)CO3,while the nanocomposites 2 reveal TOF= 87287 lr‘fur the substrate Ce(OH)CO3 and TOF=97746 fur the substrate Y(OH)CO3 under other equal conditions.In addition,nanocomposites 2”work”at room temperature giving a high yield of the desired product. It is noted that the support nanoparticles Y(OH)CO3 and Ce(OH)CO3 also exhibit catalytic activity.The yield of the final product ofthe reaction using them as catalysts is 55%(TOF=1 1 and 8 h~,respectively).Thus,the use of yttrium and cerium hydroxycarbonates as supports allows to decrease the palladium content in the nanocomposites to O.01%-1%and,consequently,reduce the cost of the catalyst while maintaining its high catalytic activity. Key words:palladium nanoparticles;support;Y(OH)CO3;Ce(OH)CO3;nanocomposites;Suzuki reaction; catalytic activity CLC number:TQ032 Document Code:A Article ID:1004.0676(2012)S1-0076—03
One of the factors limiting the application of the palladium catalysts in the hydrogenation,formation of carbon—carbon bond,oxidation and reduction in fuel cells,etc.processes is their cost.Therefore,the main task fur the researchers is to decrease the content of Pd in the catalyst while maintaining or increasing its catalytic activity
Received date:2012.08.01 Plenary report N0.Sl GALANTSEVA M.V.et all Synthesis of Camlytic Systems Based on Nanocomposites Containing Palladium and Hydroxyearbonates ofRare。Earth Elements 77
by using supports. IrI tlle present work we have investigated the catalytic activity of the nanocomposites containing palladium nanoparticles immobilized on the yttrium and cerium hydroxycarbonate supports.The Suzuki cross—coupling reaction was chosen as a model one(the scheme is shown in Fig.1),as it is widely used for the synthesis ofbiaryls acting ligands and precursors in the synthesis of polymers,liquid crystals,as well as pharmaceuticals. Traditionally,the Suzuki reaction is catalyzed by organic solvents soluble palladium complexes with coordinated phosphines,but the complexity of the separation and recovery of the catalyst in homogeneous catalysis makes the
heterogeneous one more attractive.
B(OH)2+ cat. ———————■一..
C2H5OH,K3PO4,78。C
Fig.1 Scheme of the Suzuki CROSS—coupling reaction Catalyst:Pd/Y(OH)CO3;Pd/Ce(OH)C03
Iodobenzene,C6I-I5I,and phenylboronic acid,PhB(OH)2,were chosen as starting compounds,the reaction product is biphenyl,C12H10. We investigated the following catalytic systems:Pd/Y(OH)CO3(0.01 wt%-1 wt%Pd),Pd/Ce(OH)CO3(0.01 wt%-1 wt%Vd).The reaction was conducted in the liquid phase at atmospheric pressure and constant temperature (8o士2"c,24 4-2℃)depending on the reaction time(5 min ̄2 h).The nanocomposites Pd/Y(OH)CO3 and Pd/Ce(OH)CO3 were synthesized using two methods:the first-simultaneous production of the nanoscale support and imobilization of palladium nanoparticles onto it(nanocomposites 1),the second-prior synthesis of polyvinylpirrolidone stabilized palladium nanoparticles followed by their immobilization on the nano—sized support(nanocomposites 2).The catalytic systems were characterized using scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy(EDS),their specific surface areas were measured,the conversion degree of iodobenzene was determined by gas chromatography,the reaction products were identified by H and¨C{ H} NMR spectra. The SEM analysis showed that the support Y(OH)CO3 has an almost spherical shape with pores of mean diameter 3 ̄10 am,while the support Ce(OH)C03 has an elliptical shape without pores.It was found out that the specific surface areas of the nanocomposites 1 on the support Ce(OH)CO3 are lower than the specific surface areas ofthe samples on the support Y(OH)CO3 due to the absence ofthe porosity in cerium nanoparticles and equal to 11.8(1%Pd卜14.5(0.1%Pd)mZ/g and 51.3(0.1%Pd) ̄71.7(0.5%Pd)I 儋for cerium and yttrium,