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均相沉淀法制备的纳米CeO


第 32 卷 第 4 期 2004 年 4 月

华南理工大学学报 (自然科学版) J ournal of South China University of Technology ( Natural Science Edition)

Vol . 32   No. 4 April   2004

A rticle ID

: 1000- 565 X ( 2004) 04- 0052- 05
 

0   nt r o d ucti o n I

from room temperature to its melting point as compared to other pure oxides and oxygen ion conductor , such as zirconia and bismuth oxide
[1 ]

ers , catalytic supports for automotive exhaust systems plied to ceramics , phosphors and oxygen gas sensor and solid electrolytes in so2lid oxide fuel cell
 Receive d dat e : May 9 , 2003
Foundation of China ( 50278036 , 20277010) scut . edu. cn
[3 ]

a useful material applied as glass additives , glass polish2
[2]

because of its oxidation/ reduction capacity. Thick films

of ceria can be used as advanced low2temperature water2 gas shift ca2talysts for the production of essentially car2
3 Fou n dation it e ms : Supported by the National Natural Science   Biograp hy : Yuan Wen2hui ( born in 1969) , male , associa2te
professor , Ph. D . , mainly researches on chemical engineering adsorption and environmental engineering. E2mail : cewhyuan @

St r uct u r e Cha r act e rizati on of Na nosize d Ce ri u m Oxi de Pa rticl es 3 Pr ep a r e d by Homoge ne ous Pr ecip it ati on
( Research Institute of Chemical Engineering , South China Univ. of Tech. , Guangzhou 510640 , Guangdong , China ) ) A bs t ract : A novel synthesis method based on homogeneous precipitation using cerium ( Ⅳ nitrate as the starting material was developed to prepare ultrafine cerium oxide particles . Properties of the obtained samples were characterized by XRD , DSC/ TGA , TEM and B ET area measurements . A structure of fluorite cubic phase of the prepared samples with a B ET specific surface area of 101 m2 / g was obtained. XRD results show that the prepared particles are of a large lattice parameter , which indicates that the particles are very small . Moreover , the DSC/ TGA measurement results show that the weight loss of the particles is about 16 . 84 %, manifesting that the molecular formula of cerium oxide compound is CeO2 ? H2 O . It is also indicated by TEM that the particles obtained by the 2 from CeO2 particles are of the highest CeO2 mass concentration of more than 170 g/ L and are stable for more than four weeks without any precipitation.

Cerium oxide ( ceria ) has a fluorite structure stable

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homogeneous precipitate method are spherical2like , with an average particle size of about 10 nm. The sols obtained Ke y wor ds : nanosized particle ; cerium oxide ; structure characterization ; homogeneous precipitation CL C n u m be r : O 643 . 32      Doc u me nt code : A

. It has been considered as

Yuan Wen2hui  Bi Huai2qing  Wei Chao2hai coprecipitation
[ 11 ] [ 10 ]

change Membrane ) fuel cells [ 5 ] .

sors

, or ap 2
[4 ]

,

factant synthesis [ 15 ] have been applied to prepare pow2 dered ceria and its precursors . Nanosized ceria particles tend to agglomerate in the sol or during the calcination. This would be harmful to sol stability or cause a decrease in the specific surface area of the powder. The extent of agglomeration depends on the surface properties of the nanocrystalline particles in the powder. These properties are strongly dependent on powder synthesis procedures . For example , in densely agglomerated nanostructured powders , there are many contact points among primary erated powders should begin with the starting powder and the preparation procedure .
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sis [ 13 ] , urea2based homogenous precipitation[ 14 ] and sur2

sition treatment . The optimal control of weakly agglom2

particles which allow sufficient diffusion producing ag2

bon mono2xide free hydrogen to feed PEM ( Proton Ex2 Hydrothermal synthesis [ 6 , 7 ] , spray pyrolysis [ 8 , 9 ] , , forced hydrolysis
[ 12 ]

glomeration even in a low2temperature thermal decompo2

, decomposition of oxalate precur2

, electrochemical synthe2

    4 No.

spherical , weakly agglomerated ceria ceramic particles

flux was kept for 4 h at 100 ℃ Yellow precipitates . oven at 40 ℃ for two days .

size ultrafine weakly2agglomerated ceria powders . The approach used in this paper is homogenous precipitation um precursor. The solid oxide precursors and ceria are characterized by Adsorption Porosimeter , DSC , TGA , XRD and TEM .

sition and to estimate the crystalline size of the powders

tioned obstacles . The objective of this work is to synthe2

1  Exp e ri m e nts
1 . 1   y nt hesis S

cibles in air till to 450 ℃ with a heating rate of

terized to determine their particle size , composition and morphology. XRD analysis ( Siemens D2500 , Cu K , α

size was estimated by peak broadening using the Scherrer

tallite size , λ is the wavelength of the XRD peak , θ is

peak ( 111) . The B ET speci2fic surface area , pore vol2 ume , pore size and average pore size of the calcined powders were obtained from N2 sorption isotherms ( AS2 AP 2000 , Micromeritics ) . DSC/ TGA ( SD T 2960 Si2

that can be used to prepare the thick film of ceria by sol2 the solution is 0 . 34 . In the hydrolysis duration , the mole ratio of H
+

0 . 5 ℃ min for 3 h. /

1 . 2  Cha r act e riza ti o n

0 . 154 06 nm) was used to determine the phase compo2

the diffraction angle , and βis the corrected half2width of

) with cerium ( Ⅳ nitrate as the starting material of ceri2 neck flask equipped with a thermometer and a reflux condenser at the ambient temperature . The p H value of
4+

were then obtained , which were filtered and dried in an

θ with a 2 range of 20 ° 80 ° The apparent crystallite ~ .

[ 16 ] equation : D = 0 . 9λ (β θ / cos ) , where D is the crys2

gel method ( dip2coating ) because of the above2men2 to Ce is about 2 . 14 . The reaction

medium was maintained by vigorous stirring and the re2 Synthesized powders were calcined in alumina cru2 The precipitated and calcined samples were cha2rac2

   Few studies have been carried out to obtain so2lid ,

Ceric nitrate and H2O were introduced into a three2

  Yuan Wen2hui et al : Structure Characterization of Nanosized Cerium Oxide Particles   Prepared by Homogeneous Precipitation

53

phology of samples was characterized by TEM ( Phillips

cohol and evaporated on the grid at room temperature .

2  Res ul ts a n d Disc ussi o n
2 . 1   u rf ace M orp hol ogy S

? 1994-2011 China Academic Journal Electronic Publishing House. All rights reserved.

pared samples . The specific surface area and specific to2 tal pore volume of the samples decrease with the increasing of calcination temperature . As shown in Table

specific surface area of 10 . 6 m / g.

cording to the mechanism proposed by Lin et al [ 17 ] , this

phenomenon attributes to the shrin2kage of intraparticle cause the pore size is reduced. This indicates that the samples are weakly aggregated. During the calcinations at the temperature of 450 ~ 600 ℃, the B ET specific quickly formed. ria prepared after drying at 40 ℃ and calcining at dried at 40 ℃, estimated from the TEM image , is about

pores rather than the formation of new bigger pores be2 cinations at the temperature of 600 ~ 800 ℃, the B ET cluded that aggregated particles and big crystallites are cle size and shape . Fig. 1 shows the TEM images of ce2 specific surface area decreases very abruptly. It is con2

surface area slowly decreases . However , during the cal2

multaneous DSC2TGA ) curves were obtained in a dry2air

1 , the sample calcined at 450 ℃ has a larger micropore
2

the samples decreases and , after reaching a minimum of

5 . 4 nm , increases with the calcination temperature . Ac2 450 ℃ The average size ( diameter ) of ceria sample .
TEM analysis provides the information about parti2
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atmosphere with a heating rate of 5 ℃ min. The mor2 /
Table 1   Pore structure of samples
Micropore specific surface area / (m2?- 1) g Calcination temperature / ℃ B ET specific surface area / (m2?- 1) g Specific total pore volume / (cm3?- 1) g Average pore diameter / nm

CM20) and the samples were dispersed in pure ethyl al2
450 500 600 800 900

As shown in Table 1 , the average pore diameter of

Table 1 summarizes the pore structure of the pre2
101 10 . 6 10 . 1 0 . 162 0 0 . 155 8 0 . 144 4 0 . 026 9 0 . 025 7 6. 4 5. 7 5. 4 9. 0 9. 6 98 92 12 10 9. 5 8. 0 6. 8

54

J ournal of South China University of Technology ( Natural Science Edition)

Vol . 32

ical shape . After being calcined at 450 ℃, the particle is of a size about 7 ~ 8 nm , and its shape is almost

spherical , as shown in Fig. 1 ( b ) . The measured value

B ET , which indicates that these particles are much more difficult to agglomerate .

° 47. 0 ° 55. 7 ° characterizing the fluorite structure , and ,
with a larger lattice parameter (0 . 551 4 nm) . As shown

from Ce ( NO3 ) 4 precursors after drying at 40 ℃ and cal2 cining at 450 ℃ and 800 ℃ The peaks of the dried . sample were detected at 22 . 1 ° 27 . 9 ° 32 . 5 ° 44 . 4 , , ,

4 nm , as shown in Fig. 1 ( a ) . The particle is of a spher2
of particle size is in agreement with the calculated one of
Fig. 1  TEM photographs of CeO2 particles prepared from Ce ( NO3 ) 4

θ in Fig. 2 , the 2 value increases with the increasing of
creases . calcination temperature , while the lattice parameter de2
Fig. 2   XRD spectra of CeO2 powders prepared from Ce ( NO 3 ) 4
a — 2prepared powders ; b — As Powders calcined at 450 ℃; c— Powders calcined at 800 ℃
[ 18 ]

Many factors , such as surface stress and other . In the
3+ 4+

atomic forces , affect the lattice expansion case of using Ce acid condition , it is hard to substitute Ce
4+

materials as the precursors and in with Ce in

the fluorite lattice . It could be suggested that the surface stress affects the lattice expansion , which derives from nough as the single crystallite size and comparing with the crystallite size , the existence of hydrogen atoms

tice expansion.

2 . 3  Res ults of The r m al A nal ysis

theoretical ones for plausible decomposition reactions ,

2 . 2  Cr ys t al S t r uct u r e a n d Size

Fig. 2 shows the XRD spectra of samples prepared

? 1994-2011 China Academic Journal Electronic Publishing House. All rights reserved.

the chemical composition of the precipitates can be de2 ment . This chemical composition refers to CeO2? 2O , nH which is hydrated or partially hydrated with the crystalline drated oxide , i . e. CeO2?H2O , has a theoretical weight 2 loss of 17 . 29 %. The obtained precipitate shows a total weight loss within the n value range from 0 to 2 . The completely hy2 of 16 . 84 % , as shown in Fig. 3 . The calculated value of n is about 1 . 94 . This total weight loss corresponds well
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duced from the thermo2gravimetric weight loss measure2

would change the surface stress , thus leading to the lat2 By comparing the measured weight losses to the

hydrogen atoms . Assuming the particle size is small e2 bonded to the lattice oxygen through hydrogen bond

    4 No.

with that expected for Ce ( OH ) 4 / CeO 2 ? H2O . Three        2

main temperature regions are distinguished , one is at

tween about 100 ℃ to 270 ℃, followed by a terminat2 ing step covering a temperature range of about 300 ~ at 70 ℃ in the DSC curve , which corres2ponds to the Ce ( OH) 4 , which appears at 220 ℃ reported by Rossignol
[ 19 ]

450 ℃ The first region consists of an endothermic peak .
loss of adsorbed water. Two more endothermic peaks at

313 ℃ and 436 ℃ are shown in the DSC curve . The
the fluorite2type structure from the amorphous et al
) Ce ( Ⅳ precursor

former peak most possibly attributes to the formation of

2 . 4  CeO2 S ol Pr ep a r a ti o n

ders into distilled water. The powders were carefully

ing to 70 ℃ until a clear milky sol was obtained. The stability of the samples are shown in Table 2 . The sols are of a p H range of 1 . 0 ~ 4 . 0 and the highest mass

tration and are stable for a shorter time .

peptized with the addition of HNO3 by stirring and heat2 concentration up to 170 g/ L stable for more than a month without any precipitation. The sols derived from mass concentration and are stable for a longer time , the particles calcined at 450 ℃ and 600 ℃ are of higher while those calcined at the temperature lower than

450 ℃ or more than 600 ℃ are of lower mass concen2

about 70 ℃, another is within a temperature range be2 . The latter attributes to the surface stress change when the water loss occurs by breaking the hydrogen atoms bonded to the lattice oxy2gen via hydrogen bond.
Fig. 3   DSC/ TGA curves of the powders prepared from

CeO 2 sols were obtained by dissolving CeO2 pow2

  Yuan Wen2hui et al : Structure Characterization of Nanosized Cerium Oxide Particles   Prepared by Homogeneous Precipitation
calcined at different temperatures
The highest mass concentration / (g? L
-1

55

Table 2   Stability of the sols derived from the precursors

3   ncl usi o ns Co

homogeneous method under reflux condition by using Ce ( NO3 ) 4 as the starting material . This method is of a great deal of advantages . For example , the obtained

cerium oxide particles are very fine ( with a diameter of about 4 nm after drying and 7 ~ 8 nm after calcined at with the molecular formula of CeO2 ?H2O . The sols de2 2 Ref e r e nces :
[1]   Michizuki X. Infrared optical properties of cerium dio2xide [J ] . Phys Status Solidi B , 1982 , 114 : 189 - 195 . [2]   Fornasiero P ,Balducci G ,Monte Di R ,et al . Modification of with ZrO2 [J ] . J Catal , 1996 , 164 : 173 - 183 . Soc , 1988 , 135 ( 8) : 2 077 - 2 086 . storage properties [J ] . App Catal B , 1998 , 15 : 107 - 114 . tragonal ZrO2 powder under hydrothermal conditions [J ] . J Mater Sci Letter , 1982 , 1 ( 11) : 461 - 466 . [7]   Hirano M , Kato E. The hydrothermal synthesis of ultrafine cell with ceria2yttria solid Electrolyte [ J ] . J Electrochem materials [J ]. Catal Rev Sci Eng ,1996 ,38 :439 - 520. ( 14) : 1 249 - 1 250 . the redox behaviour of CeO2 induced by structural coping [ 3 ]  Yahiro H , Baba Y , Eguchi K , et al . High temperature fuel [ 4 ]  T rovarelli A. Catalytic properties of ceria and CeO22containing [5]   Bunluesin T ,J gorte R. Studies of the water2gas2shift reaction [ 6 ]  Tani E , Yoshimura M , Somiya S. Formation of ultrafine te2 ) cerium ( Ⅳ oxide powders [J ] . J Mater Sci Letter , 1996 , 15

est CeO2 mass concentration more than 170 g/ L .

? 1994-2011 China Academic Journal Electronic Publishing House. All rights reserved.

rived from the obtained particles are stable with the high2
on ceria2supported Pt , Pd , and Rd : Implications for oxygen2

) 450 ℃ and spherical , which are weakly agglome2rated
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Calcination temperature of sol pre2 cursors / ℃

pH range

Stability

)

150 250 350 450 600 700 800

1 . 5~3 . 5 1 . 5~3 . 5 1 . 5~4 . 0 1 . 0~4 . 0 1 . 0~4 . 0 1 . 0~4 . 0 1 . 0~4 . 0

20 50

Stable (more than two weeks) Stable (more than two weeks) Stable (three weeks) Stable (more than four weeks) Stable (more than four weeks) Stable (more than three weeks) Stable (more than three weeks)

110 170 170 120 110

) Nanosized Ce ( Ⅳ oxide powder was prepared by the

56

J ournal of South China University of Technology ( Natural Science Edition)

Vol . 32

[ 8 ]   H , Gu L , Guo J , et al . Synthesis of solid spherical CeO2 Xu particles prepared by the spray hydrolysis reaction method [J ] . J Am Ceram Soc , 2002 , 85 ( 1) : 139 - 144. [9]   Vallet2T M , Conde G , Nicolopoulos S , et al. Synthesis and egi characterization of CeO2 obtained by spray pyrolysis method [J ]. Mater Sci Forum Vols , 1997 ,235 :291 - 295. [ 10 ]  Kirk T J , Winnick J . A hydrogen sulfide solid2oxide fuel

[ 14 ]   Matijevic E , Hsu W P. Preparation and properties of monodispersed colloidal particles of lanthanide compounds [J ]. J Colloid Interface Sci , 1987 ,118 :506 - 523. [ 15 ]   Chu X , Chung W , Schmidt L D . Sintering of sol2gel pre2 [ 16 ]  Terribile D , Trovarelli A ,Llorca J , et al . The synthesis and [ 17 ]   Lin Y S , Chang C H , Gopalan R. Improvement of thermal stability of porous nanostructured ceramic membranes [J ] . Ind Eng Chem Res , 1994 , 33 : 860 - 870 . [ 18 ]   Perry R H , Chilton C H. Chemical Engineering Handbook [ M ] . 5th ed. New York :McGraw2Hill , 1995 . pared submicrometer particles studied by transmission elec2 tron microscopy [J ] . J Am Ceram Soc , 1993 , 76 ( 8) : 2 115

- 2 118 .

1993 , 12 : 3 494 - 3 496 .

摘  要 : 采用均相沉淀法 , 以 Ce ( NO3 ) 4 为起始原料制得了一种具萤石立方相结构 、 ET 比表面积为 B
101 m2 / g的 CeO2 超细颗粒 . 同时采用 XRD 、 DSC/ TGA 、 TEM 和 B ET 表面测定法对样品性能进行了表征 .

失重为 16 . 84 % , 由此可推断 CeO2 化合物的分子式为 CeO2 ?H2O ; 从 TEM 测试结果来看 , 均相沉淀法制备的 2 CeO2颗粒平均直径为 10 nm , 颗粒为球状 . 将所制得的 CeO2 颗粒用来制备溶胶 , 其最大质量浓度可达 170 g/
L , 稳定期可达 4 周以上且无任何沉淀 .

关键词 : 纳米颗粒 ; 氧化铈 ; 结构表征 ; 均相沉淀 中图分类号 : O 643 . 32      文献标识码 : A 文章编号 : 1000- 565 X ( 2004) 04- 0052- 05

[ 11 ]   Herle J V , Horita T , Kawada T , et al . Fabrication and sin2 [ 12 ]   Hsu W P , Ronnquist L , Matijevic E. Preparation and prop 2 erties of monodispersed colloidal particles of lanthanide ) compounds (2) : Cerium ( Ⅳ [J ] . Langmuir , 1988 , 4 : 31 [ 13 ]  Zhow Y , Philips R J ,Switzer J A . Eloctrochemical synthesis and sintering of nanocrystalline cerium oxide powders [J ] . J

XRD 结果表明 , 所制得的颗粒具有较大的晶格参数 , 说明颗粒较小 ; DSC/ TGA 测试结果表明 , 所制备的颗粒

  收稿日期 : 2003 - 05 - 09

3 基金项目 : 国家自然科学基金资助项目 ( 50278036 , 20277010)

  作者简介 : 袁文辉 ( 1969 - ) , 男 , 副研究员 , 博士 , 主要从事化工吸附和环境工程研究 . E2mail : cewhyuan @scut . edu. cn ? 1994-2011 China Academic Journal Electronic Publishing House. All rights reserved. http://www.cnki.net

tering of fine yttria2doped ceria powder [J ] . J Am Ceram Soc , 1997 , 80 ( 4) : 933 - 940 .

34 .

Am Ceram Soc , 1995 , 78 (4) :981 - 985.

cell using ceria2based electrolytes [J ] . J Electrochem Soc ,

pared using hybrid organic/ iorganic route [ J ] . J Catal ,

1998 , 178 : 299 - 309 .

均相沉淀法制备的纳米 CeO2 颗粒的结构表征 3
袁文辉   毕怀庆   韦朝海
( 华南理工大学 化学工程研究所 , 广东 广州 510640)

[ 19 ]   Rossignol S , Madier Y , Duprez D . Preparation of zirconia2 ceria materials by soft chemistry [J ] . Catal Today , 1999 ,

50 : 261 - 270 .

characterization of mesoporous high2surface area ceria pre2

责任编辑 : 傅晓琴


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