Pd@Au核壳结构纳米颗粒在CO和O_2中动态变化的原位电镜研究
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摘要
由于其广泛的催化适用性及优异的催化性能,PdAu双金属纳米催化剂一直以来都备受重视。本文以Pd@Au球形纳米颗粒为研究对象,使用气体样品杆系统在透射电子显微镜中原位观察了300℃退火过程中,纳米颗粒在一个大气压的CO或O_2环境下的动态变化。实验发现,Pd@Au球形纳米颗粒在CO中发生剧烈的形貌变化,暴露出大量的{111}面。CO在PdAu合金表面的选择性吸附可能是发生形貌变化的主要原因。而在O_2气氛中,Pd在300℃退火条件下向颗粒表面快速析出并形成PdO团簇。Pd@Au纳米颗粒在300℃下的快速合金化以及O_2对Pd的诱导作用是形成该变化的原因。依靠着Au壳层的保护,Pd@Au纳米颗粒的核壳结构在300℃以下可以保持稳定。
Pd@Au bimetallic nanoparticles have received considerable attention for their excellent catalytic activity. In this work,the transformation process of spherical Pd@Au core-shell nanoparticles in CO and O_2( 1 atm) during annealing at 300 ℃ with a gas holder system was studied. It was revealed that the spherical Pd@Au nanoparticle refaceted into an octahedron nanoparticle due to the anisotropy adsorption of CO on PdAu alloy surfaces,which induced the surface energy change,resulting in more exposure of { 111}facets. While annealing in O_2,Pd atoms migrate outward with the assistance of O_2 and were oxidized to PdO at 300 ℃. In addition,it was found that the core-shell structure was stable below 300 ℃ because of the protection of Au shell.
Pd@Au bimetallic nanoparticles have received considerable attention for their excellent catalytic activity. In this work,the transformation process of spherical Pd@Au core-shell nanoparticles in CO and O_2( 1 atm) during annealing at 300 ℃ with a gas holder system was studied. It was revealed that the spherical Pd@Au nanoparticle refaceted into an octahedron nanoparticle due to the anisotropy adsorption of CO on PdAu alloy surfaces,which induced the surface energy change,resulting in more exposure of { 111}facets. While annealing in O_2,Pd atoms migrate outward with the assistance of O_2 and were oxidized to PdO at 300 ℃. In addition,it was found that the core-shell structure was stable below 300 ℃ because of the protection of Au shell.
引文
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[2]XU J,WHITE T,LI P,et al.Biphasic Pd-Au alloy catalyst for low-temperature CO oxidation[J].J Am Chem Soc,2010,132(30):10398-10406.
[3]SOLSONA B E,EDWARDS J K,LANDON P,et al.Direct synthesis of hydrogen peroxide from H2and O2using Al2O3supported Au-Pd catalysts[J].Chem Mater,2006,18(11):2689-2695.
[4]LANDON P,COLLIER P J,CARLEY A F,et al.Direct synthesis of hydrogen peroxide from H2and O2using Pd and Au catalysts[J].Phys Chem Chem Phys,2003,5(9):1917-1923.
[5]ENACHE D I,EDWARDS J K,LANDON P,et al.Solvent-free oxidation of primary alcohols to aldehydes using Au-Pd/Ti O2catalysts[J].Science,2006,311(5759):362-365.
[6]XIE S H,TSUNOYAMA H,KURASHIGE W,et al.Enhancement in aerobic alcohol oxidation catalysis of Au-25 clusters by single Pd atom doping[J].ACSCatalysis,2012,2(7):1519-1523.
[7]ZHANG L,NIU W X,GAO W Y,et al.Synthesis of convex hexoctahedral Palladium@Gold core-shell nanocrystals with{431}high-index facets with remarkable electrochemiluminescence activities[J].ACS Nano,2014,8(6):5953-5958.
[8]ZHANG L,NIU W X,LI Z Y,et al.Facile synthesis and electrochemiluminescence application of concave trisoctahedral Pd@Au core-shell nanocrystals bound by{331}high-index facets[J].Chem Commun,2011,47(37):10353-10355.
[9]ZHAO R P,GONG M X,ZHU H M,et al.Seedassisted synthesis of Pd@Au core-shell nanotetrapods and their optical and catalytic properties[J].Nanoscale,2014,6(15):9273-9278.
[10]TAO F,GRASS M E,ZHANG Y W,et al.Reactiondriven restructuring of Rh-Pd and Pt-Pd core-shell nanoparticles[J].Science,2008,322(5903):932-934.
[11]LEE A F,ELLIS C V,WILSON K,et al.In situ studies of titania-supported Au shell-Pd core nanoparticles for the selective aerobic oxidation of crotyl alcohol[J].Catal Today,2010,157(1/2/3/4):243-249.
[12]JIN M,LIU H,ZHANG H,et al.Synthesis of Pd nanocrystals enclosed by{100}facets and with sizes<10 nm for application in CO oxidation[J].Nano Res,2010,4(1):83-91.
[13]GAO Q,JU Y M,AN D,et al.Shape-controlled synthesis of monodisperse PdCu nanocubes and their electrocatalytic properties[J].Chem Sus Chem,2013,6(10):1878-1882.
[14]盛丽萍,王勇,张泽.PtNi纳米颗粒在氧气中结构变化的原位电镜研究[J].电子显微学报,2018,37(5):391-396.
[15]PENNYCOOK S J,RAFFERTY B,NELLIST P D.Z-contrast imaging in an aberration-corrected scanning transmission electron microscope[J].Microsc Microanal,2000,6(4):343-352.
[16]李斗星.透射电子显微学的新进展II Z衬度像、亚埃透射电子显微学、像差校正透射电子显微学[J].电子显微学报,2004,23(3):278-292.
[17]JIANG Y,LI H,WU Z,et al.In situ observation of hydrogen-induced surface faceting for palladium-copper nanocrystals at atmospheric pressure[J].Angew Chem Int Ed Engl,2016,55(40):12427-12430.
[18]ZHANG X,MENG J,ZHU B,et al.In situ TEMstudies of the shape evolution of Pd nanocrystals under oxygen and hydrogen environments at atmospheric pressure[J].Chem Commun,2017,53(99):13213-13216.
[19]WU Z,TANG M,LI X,et al.Surface faceting and compositional evolution of Pd@Au core-shell nanocrystals during in situ annealing[J].Phys Chem Chem Phys,2019,21(6):3134-3139.
[20]DELANNOY L,GIORGIO S,MATTEI J G,et al.Surface segregation of Pd from Ti O2-supported Au Pd nanoalloys under CO oxidation conditions observed in situ by ETEM and DRIFTS[J].Chem Cat Chem,2013,5(9):2707-2716.
[21]TEIXEIRA-NETO A A,GONCALVES R V,RODELLAC B,et al.Surface composition and structural changes on titanium oxide-supported Au Pd nanoparticles during CO oxidation[J].Catal Sci Technol,2017,7(8):1679-1689.