第 38 卷第 3 期 中南民族大学学报( 自然科学版) Vol．38 No．32019 年 9 月 Journal of South-Central University for Nationalities( Natural Science Edition) Sep．2019

收稿日期 2018-09-30作者简介 朱君江( 1977-) ，男，教授，博士，研究方向: 多相催化，E-mail: ciaczjj@ 163．com基金项目 国家自然科学基金资助项目( 21203254) ; 湖北省自然科学基金重点资助项目( 2015 CFA138) ; 辽宁省自然科

学基金资助项目( 201602681) ; 沈阳市科技计划基金资助项目( 17-76-1-00)

Sol-gel preparation of La1－x Cex CoO3

for CO oxidation: effect of Ce dopingZHU Junjiang 1，2，3，WANG Shan 1，XU Xuelian 1，ZHAO Yanxi 3，YANG Haijian 3

( 1 Institute of Catalysis for Energy and Environment，College of Chemistry and Chemical Engineering，Shenyang Normal University，

Shenyang 110034，China; 2 Hubei Key Laboratory of Biomass Fibers and Eco-dyeing ＆ Finishing，College of Chemistry and

Chemical Engineering，Wuhan Textile University，Wuhan 430200，China; 3 Key Laboratory of Catalysis and Materials

Science of the State Ethnic Affairs ＆ Commission Ministry of Education，College of Chemistry and Materials Science，

South-Central University for Nationalities，Wuhan 430074，China )

Abstract La1－xCexCoO3 perovskite catalysts were prepared by sol-gel method and characterized by XＲD，N2 physisorption

and H2-TPＲ measurements． The effects of Ce doping on the physicochemical properties and catalytic performances of

La1－xCexCoO3 for CO oxidation were investigated．The results indicated that the doping of Ce into the perovskite framework

not only increased the BET surface area，but also enhanced the redox performance and improved the CO oxidation activity．

However，when the Ce doping percentage was more than 10%，CeO2 phase appeared in the sample，which covered the active

site and resulted in the destruction of perovskite structure，decreasing the CO oxidation activity．

Keywords perovskite oxides; LaCoO3 ; Ce doping; CO oxidation

中图分类号 O643．36 文献标识码 A 文章编号 1672-4321( 2019) 03-0350-07

DOI 10．12130 /znmdzk．20190306

引用格式 朱君江，王珊，许雪莲，等．溶胶-凝胶法制备 La1－xCexCoO3催化 CO 氧化性能: Ce 掺杂的影响 ［J］．中南民

族大学学报( 自然科学版) ，2019，38( 3) : 350-356．

ZHU Junjiang，WANG Shan，XU Xuelian，et al．Sol-gel preparation of La1－xCexCoO3 for CO oxidation: effect of Ce doping

［J］．Journal of South-Central University for Nationalities ( Natural Science Edition) ，2019，38( 3) : 350-356．

溶胶 - 凝胶法制备 La1-x Cex CoO3 催化 CO 氧化性能: Ce 掺杂的影响朱君江1，2，3，王珊1，许雪莲1，赵燕熹3，杨海健3

( 1 沈阳师范大学 化学化工学院 能源与环境催化研究所，沈阳 110034;

2 武汉纺织大学 化学与化工学院 生物质纤维与生态染整湖北省重点实验室，武汉 430200;

3 中南民族大学 化学与材料科学学院 催化材料科学国家民委-教育部共建重点实验室，武汉 430074)

摘 要 以溶胶-凝胶法制备了 La1－xCexCoO3钙钛矿催化剂，并用 X-射线衍射、N2物理吸附和 H2程序升温还原等对其进行了

表征．考察了 Ce 掺杂对 La1－xCexCoO3物化性能及其催化 CO 氧化性能的影响．结果表明: Ce 的掺杂不仅增加了样品的比表面

积，还增强了其氧化还原性能，提高了样品对 CO 的氧化活性．但当 Ce 掺杂量( 即 Ce /La+Ce 原子比) 大于 10%时，样品中出现

CeO2物相，覆盖了活性位，破坏了钙钛矿结构，使 CO 氧化活性下降．

关键词 钙钛矿氧化物; LaCoO3 ; Ce 掺杂; CO 氧化

Perovskite oxides with ABO3 structure are a typeof ideal model catalyst for investigation inheterogeneous catalysis，in that the metal cations atboth A-and B-site can be substituted by foreign metalcations without destroying the matrix structure，as longas the tolerance factor is in the range of 0．7 ～ 1．1［1］．Therefore，the physicochemical properties of perovskiteoxides can be tailored as desired，and its relation to thestructure properties can be feasibly correlated．

The application of perovskite oxides in catalysiscame into view since the report of Voorhoeve et al． in1972［2］，who found that these materials were active forhydrocarbons oxidation． Thereafter，a large number ofworks regarding the catalytic applications of perovskiteoxides have been explored［3］ and great achievementshave been obtained． It is generally believed that oxygenvacancy and redox ability are two important propertiesof the material［1，4］． The former is used to absorb andactivate the oxidant，e． g．，molecular oxygen，and thelatter is to catalyze the electron-transfer reactionbetween the reactant and the catalyst． Whereas，therelation between them is hard to separate，as thegeneration of oxygen vacancy would change inevitablythe oxidation states of the B-site cations，and thus altersthe redox ability．

The regeneration of oxygen vacancy is crucial tobe considered when preparing perovskite catalysts foroxidation reactions，as the oxygen vacancy would berepaired when oxygen is present，leading to deactivationof the catalyst． To regenerate the oxygen vacancy andenable the reaction to be proceeded smoothly，twostrategies can be adopted: by raising the reactiontemperature or adding a material that can promote themobility of atomic oxygen to the structure．

From the viewpoint of energy savings，it ispreferable to improve the ability of catalyst for oxygenmobility． In this respect，cerium is a promising materialand receives special interest both in academic studiesand in practical use，because of its unique ability foroxygen storage and release． Zhu et al［5］ reported that

the doping of Ce to La1－x Cex CoO3 increasedsignificantly the activity for aerobic oxidation of benzylalcohol to benzaldehyde due to the stronger affinity ofCe to O atoms ( relative to that of La ) ，and theoptimum Ce content ［atomic ratio of Ce / ( La +Ce) ］

was 10%． Gao et al［6］ found that the Ce doping couldincrease the specific surface area and reduce thecrystallite size of La1－x Cex CoO3，thus improve theactivity for plasma-catalytic oxidation of lowconcentration ethyl acetate ( 100 ) ． Xiang et al［7］

reported that the presence of Ce4+ in La1－x Cex FeO3

could strengthen the interactions with adsorbed O2 andfacilitate the activation of O—O bond， andconsequently accelerate the reaction rate of catalyticmethane combustion，with the optimum Ce content of30%． All these results suggested that the Ce dopingwas effective to improve the catalytic performances ofperovskite oxides，by increasing the surface area，

strengthening the interaction with adsorbed oxygen，

improving the reducibility，and so on．In this work，a series of Ce-doped La1－xCexCoO3

perovskites were prepared，and the effect of Ce dopingon the physicochemical properties and catalyticperformances of LaCoO3 were investigated． XＲD，N2-physisorption，O2-TPD and H2-TPＲ measurements wereused to demonstrate the change of properties caused byCe doping． Catalytic CO oxidation，which is an efficientroute to eliminate CO from the exhausts and is a widelyused model reaction［8］，was selected to evaluate thecatalytic performances of catalysts． First，the activitiesof perovskite oxides with different transition metals forCO oxidation were screened to optimize the transitionmetal． Thereafter，LaCoO3 was selected and the effect ofCe doping on CO oxidation activity was investigated，tooptimize the Ce content． The results indicated that theoptimum Ce content was 10%，i． e．，La0．9 Ce0．1 CoO3，at

which most of the Ce3+ ions entered the perovskiteframework，leading to enhanced surface area and redoxability，and enhance the activity for CO oxidation，withon-set temperature of 75 ℃ ．

153第 3 期 朱君江，等: 溶胶-凝胶法制备 La1-xCe xCoO3催化 CO 氧化性能: Ce 掺杂的影响

1 Experimental

1．1 PreparationThe procedure is similar as reported elsewhere［5］．

Stoichiometric amount of La ( NO3 ) 3，Ce ( NO3 ) 3 andCo( NO3 ) 2 were dissolved in distilled water，to whichcitric acid，in 1． 2 times of the total metal ions ( i． e．La3+，Ce3+ and Co2+ ) ，was added． The mixture wasstirred for 2 h，and then dried at 100 ℃ overnight． Theresulting solid was grinded and calcined in a static airoven at 600 ℃ for 5 h，with heating rate of 1℃·min－1． Depending on the amount of Ce added，thesample was defined as La1－x Cex CoO3，where x rangesfrom 0 to 0．9．1．2 Characterizations

X-ray diffraction ( XＲD ) patterns were recordedon a powder X-ray diffractometer ( Ultima IV，Ｒigaku)

using Cu-Kα radiation with a Ni-ltered operating． Thesamples were scanned in 2θ range 20-80° with ascanning speed of 5°·min－1．

N2 physisorption isotherms were obtained from aMicromeritics TriStar II 3020 analyzer． The air werepreviously evacuated from the samples，which were thentreated at 300 ℃ for 3 h in helium atmosphere．

Temperature-programmed desorption of oxygen( O2-TPD ) was performed on a TP-5076 adsorptioninstrument ( Tianjin，China) ，with the same procedureas described in previous work［9］．

Temperature programmed reduction of hydrogen( H2-TPＲ) was performed on the same apparatus． The100-mg sample was put in the reactor and treated byN2 at 400 ℃ for 1 h． After cooling to roomtemperature，the gas was switched to H2 /N2 ( volume

ratio of 110) at a flow rate of 50 mL·min－1，andafter a stable baseline was reached，the temperature wasraised to 800 ℃ at a heating rate of 10 ℃·min－1． Theconsumption of hydrogen was recorded by TCD．1．3 Catalytic tests

CO oxidation reaction was performed in a fixed-bed tubular micro-reactor，with an internal diameter of

6 mm，a wall thickness of 1 mm and a length of 400mm． The reaction mixture ( volume ratio of Ar /CO /O2

= 93 /0． 5 /6． 5) with flow rate of 50 mL·min－1 waspassed through 0．1 g catalyst placed in the middle ofthe reactor，and the temperature was raised from 50 to150 ℃ ． At each stage，the temperature was kept for 30min before the activity tests to ensure that the reactionreaches equilibrium． The gas compositions，before andafter the reaction，were analyzed by an on-line gaschromatograph ( Agilent 7890B ) ． The activity wasevaluated by the equation: CO conversion ( %) = ［c( COin ) – c( COout) ］/c( COin ) ×100%，where c( COin )

and c ( COout ) represented the inlet and outlet COconcentrations．

2 Ｒesults and discussion

In the previous work［10］，we have shown thatLaCoO3 with perovskite structure can be yielded whenprepared by sol-gel method using citric acid ascomplexant and calcined at the temperature of 600 ℃，

while the formation of perovskite structure failed whenMn，Cu and Zn，instead of Co，was used as the B-sitemetal，due to their half-filled ( 3d54s2 for Mn) or full-filled electrons ( 3d10 4s1-2 for Cu and Zn ) in the 3dorbit． Hence，LaCoO3 was chosen for investigation inthis work and the calcination temperature was set at600 ℃ ．

Fig．1 XＲD patterns of the La1－xCexCoO3( 0．1≤x ≤1)

图 1 样品 La1－xCexCoO3( 0．1≤x ≤1) 的 X-射线衍射谱图

Fig．1 depicted the XＲD patterns of La1－xCexCoO3

( 0≤ x≤ 0． 9 ) ． As expected，LaCoO3，without Ceaddition，possessed the perovskite structure． However，the peak at 2θ = 33． 3° that assigned to the

253 中南民族大学学报( 自然科学版) 第 38 卷

characteristic peak of LaCoO3 weakened，and a newpeak at 2θ = 28° that assigned to CeO2 increased withthe Ce content，suggesting that the LaCoO3 perovskitestructure was destroyed and CeO2 was separated． TheCeO2 phase became the majority and the perovskitestructure almost disappeared at x≥0．6． This indicatedthat the incorporation of Ce into the perovskiteframework was not feasible at large amount． Previousresearches have shown that the maximum Ce contentincorporated into the ABO3-type perovskite oxides was

less than 10%［11］，supporting our results．N2 physisorption measurements showed that the

BET surface area of LaCoO3 was significantly increasedafter Ce doping，especially at Ce content of 10 % ( Fig．2a) ． The surface area and pore volume increased from9．3 m2·g－1 and 0．06 cm3·g－1 for LaCoO3 to 20. 3 m2

·g－1 and 0．11 cm3·g－1 for La0．9Ce0．1CoO3，indicatingthat the incorporation of Ce into the perovskiteframework facilitated the improvement of surface areaor the creation of pores． Indeed，a significant increasein the pore volume was observed from x= 0 to 0．1，andLa0．9Ce0．1CoO3 that accomodated the most amount of Cein the framework showed the largest pore volume．However，with the further increase of Ce content，thesurface area and pore volume decreasd due to theseparation of CeO2，which blocked the pores created inthe structure，and more seriously，destroyed theperovskite structure，as observed in the XＲD patterns．These results indicated that only the Ce thatincorporated into the perovskite structure could improvethe surface area． Fig． 2b showed the pore sizedistribution of the samples． An exception was observedat x = 0．6，which showed pore size centered at 33 nmand was possibly due to the holes made between theparticles．

Fig．3 presented the O2-TPD graph obtained fromthe Lax Ce1－x CoO3 samples． Normally，two desorptionpeaks appeared in the O2-TPD graph of perovskiteoxides，with the first one，locating at temperature below600 ℃，attributed to the oxygen chemically adsorbed onthe oxygen vacancy，and the second one，locating at

Fig．2 N2 physisorption isotherms( a) and the corresponding pore

size distribution( b) of La1－x CexCoO3 ( 0．1≤x≤1)

图 2 La1－x CexCoO3( 0．1≤x≤1) 的

氮气吸附-脱附平衡曲线( a) 和孔径分布图( b)

temperature above 600 ℃，attributed to the latticeoxygen［9，12］．

a) the graph of overview; b) the graph with magnified view at

temperature between 250 and 700 ℃

Fig．3 O2-TPD graphs of the La1-xCexCoO3( 0≤x ≤0．9)

a) 整体图; b) 250～700 ℃的放大图

图 3 样品 La1-xCexCoO3( 0≤x ≤0．9) 的 O2-TPD 曲线

Fig． 3a displays that only one obvious peak，attemperature above 700 ℃，appeared in the graph ofoverview，which could be that the first desorption peak

353第 3 期 朱君江，等: 溶胶-凝胶法制备 La1-xCe xCoO3催化 CO 氧化性能: Ce 掺杂的影响

was too weak to observe． Indeed，when magnifying thegraph at temperature of 300-700 ℃ ( see Fig． 3b ) ，adesorption peak at about 500 ℃ appeared．

For the first desorption peak，the peak areadecreased and the peak temperature increased with theincrease of Ce content． This could be that for samplesfrom x = 0 to 0．1，Ce3+ ions were incorporated into theperovskite framework and some of them weretransformed into Ce4+ ions． The presence of Ce4+ ionswould decrease the amount of oxygen vacancyaccording to the principle of electroneutrality，andstrengthen the interaction with oxygen atoms ( e． g．，Ce4+― O vs． La3+—O) because of its strong affinity，

thus leading to smaller peak area and higher peaktemperature． For samples x ≥ 0． 3，because theseparation of CeO2 phase and the destruction ofperovskite structure，the amount of oxygen vacancydecreased and no peak in the graph appeared at x≥0．6where the perovskite stucture was fully destroyed．

For the second desorption peak，the peak areaincreased all alone with the Ce contents，in accordanceto what had been reported in the previous work［13］． Theincrease from x = 0 to 0．1 was that the lattice oxygenwas drew and loosed by Ce3+ /4+，facilitating the releaseof lattice oxygen． The further increase at x ≥ 0．3 wasmostly attributed to the oxygen released from Co3 O4，

which was yielded accompanying the CeO2 separation，

as discussed by Alamdari et al［14］．

Fig．4 H2-TPＲ curve of the LaxCe1－xCoO3( 0≤x ≤0．9)

图 4 LaxCe1－xCoO3( 0≤x ≤0．9) 的 H2-TPＲ 曲线

Ｒedox abilities of La1－xCexCoO3 evaluated by H2-TPＲ measurements were shown in Fig． 4． In general，two reduction peaks appeared for the samples，with thefirst attributed to the reduction of Co3+ to Co2+，and the

second to the reduction of Co2+ to Co0［11，15］． The firstreduction temperature decreased greatly after Ceaddition，from 417 ℃ for LaCoO3 to 264 ℃ forLa0．9Ce0．1CoO3，indicating that the presence of Ce

promoted the reduction of Co3+ to Co2+ ． This could beattributed to the strong affinity of Ce4+ cation foroxygen，which caused the rupture of Co—O bond bythe way of Co3+—O + Ce3+ = Co2+ + Ce4+—O．Thereafter，the oxygen of Ce4+—O was rapidly removedby H2( e．g．，Ce

4+—O + H2 = Ce3+ + H2O—e– ) due to

its capability for oxygen releasing． That is，the Ce3+

cations acted as a bridge of the reaction between H2

and Co3+—O，facilitating the reduction of Co3+ to Co2+ ．As the Ce content increased，the temperature of

the first reduction peak moved toward the hightemperature region． At this time，the oxygen of Co3+—Ocouldn' t be abstracted efficiently as that ofLa0．9Ce0．1CoO3 due to the separation of CeO2 and thedestruction of perovskite structure ( Fig．1) ． Moreover，the CeO2 covered on the surface would restrain the

reduction of Co3+ ． As a result， the reductiontemperature was shifted to high regions．

As for the second reduction peak，a significantdecrease in the peak temperature is observed from x= 0to 0． 1 due to the Ce incorporation in the perovskitestructure． The co-existence of Ce3+ ions promoted therupture of Co ― O bond as discussed above，thus thereaction between H2 and Co—O could be easilyoccurred，showing reduction temperature of 509 ℃ ．Thereafter，CeO2 was separated and the perovskitestructure was destroyed，resulting in the formation ofCo2O3 and /or Co3O4． The reduction has less relation to

the Ce3+ ions，but could relate to the Ce doping，as theperovskite phase was degraded and more Co2O3 and /orCo3 O4 would be produced with the increase of Cedoping．

Fig．5 showed the CO oxidation acitivity measuredfrom LaBO3 and Lax Ce1－x CoO3． For LaBO3 withdifferent transition metals，Co was the best B-site metalfor CO oxidation，and the activity was in sequence ofLaCoO3 ＞ LaCuO3 ≈ LaNiO3 ＞ LaMnO3 ＞ LaFeO3 ＞

453 中南民族大学学报( 自然科学版) 第 38 卷

a) LaBO3( B=Mn，Fe，Co，Ni，Cu，Zn) ; b) LaxCe1－xCoO3( 0≤x≤0．9)

Fig．5 Dependence of CO conversion on the reaction

temperature obtained from LaBO3

( B=Mn，Fe，Co，Ni，Cu，Zn) and LaxCe1－xCoO3( 0≤x≤0．9)

图 5 LaBO3( B=Mn，Fe，Co，Ni，Cu，Zn) 和 LaxCe1－xCoO3

( 0≤x≤0．9) 上 CO 转化率随温度变化图

LaZnO3 ( Fig． 5a ) ，in accordance to what had been

reported in the previous work［16］． The lowest activity ofLaZnO3 could be that the perovskite structure was not

formed，and both La3+ and Zn2+ cations had stableoxidation states and were not suitable to catalyzeelectron-transfer reaction including CO oxidation．

Fig．5b presented the effect of Ce doping on theactivity of Lax Ce1－x CoO3 for CO oxidation． With theincrease of Ce doping，the activity first increased andthen decreased，with the best obtained at x= 0．1，whichshowed an on-set temperature of 75 ℃，and wassignificantly lower than that of LaCoO3 ( 90 ℃ ) ．Together with the BET surface area and the redoxability discussed in Fig．2 and Fig．3，it was inferred thatthe best CO oxidation activity of La0．9 Ce0．1 CoO3 wasattributed to the improved surface area and redoxability caused by Ce doping． However，the Ce dopingshould be controlled，otherwise it would deteriorate thereaction by separating CeO2 phase and destroying theperovskite structure．

3 Conclusion

Effect of Ce doping on the catalytic performancesof Lax Ce1－x CoO3 for CO oxidation was investigated．XＲD patterns indicated that the content of Ce doping tothe perovskite framework was less than 10 %，otherwiseCeO2 phase would be separated and the perovskitestructure would be destroyed． Therefore，the samplewith 10% Ce doping showed the largest BET surfacearea，the best redox ability and the highest COoxidation activity． It could be explained that at high Cedoping，the pores were blocked，the structure wasdestroyed，and the active sites were covered by theseparated CeO2 phase，thus leading to decreasedactivity．

Ｒeferences

［1］ PENA M A，FIEＲＲO J L． Chemical structures and

performance of perovskite oxides ［J］． Chem Ｒev，2001，

101( 7) : 1981-2017．

［2］ VOOＲHOEVE Ｒ J H，JOHNSON D W，ＲEMEIKA J P，et

al．Perovskite oxides: materials science in catalysis ［J］．

Science，1977，195( 4281) : 827-833．

［3］ 朱君江，钟林赟，黄栾清，等．不同形貌 LaBO3型钙钛矿

的制备及其催化 H2O2分解反应性能［J］．中南民族大

学学报( 自然科学版) ，2014，33( 4) : 6-11．

［4］ ZHU J，LI H，ZHONG L，et al． Perovskite oxides:

preparation， characterizations， and applications in

heterogeneous catalysis ［J］． ACS Catal，2014，4 ( 9 ) :

2719-2940．

［5］ ZHU J，ZHAO Y，TANG D，et al． Aerobic selective

oxidation of alcohols using La1－x Cex CoO3 perovskite

catalysts［J］．J Catal，2016，340: 41-48．

［6］ ZHU X，ZHANG S，YANG Y，et al．Enhanced performance

for plasma-catalytic oxidation of ethyl acetate over

La1-xCexCoO3+δcatalysts［J］．Appl Catal B-Environ，2017，

213: 97-105．

［7］ XIANG X P，ZHAO L H，TENG B T，et al． Catalytic

combustion of methane on La1－xCexFeO3 oxides［J］．Appl

Surf Sci，2013，276( 276) : 328-332．

［8］ SEYFI B，BAGHALHA M，KAZEMIAN H． Modified

553第 3 期 朱君江，等: 溶胶-凝胶法制备 La1-xCe xCoO3催化 CO 氧化性能: Ce 掺杂的影响

LaCoO3 nano-perovskite catalysts for the environmental

application of automotive CO oxidation［J］．Chem Eng J，

2009，148( 2) : 306-311．

［9］ YU K，DIAO T， ZHU J， et al． Perovskite oxides

La0．8Sr0．2Co1－xFexO3 for CO oxidation and CO + NO

reduction: Effect of redox property and surface

morphology ［J］． Chem Ｒes Chinese U，2018，34 ( 1 ) :

119-126．

［10］ WANG S，ZHANG Y B，ZHU J，et al．Sol-Gel preparation

of perovskite oxides using ethylene glycol and alcohol

mixture as complexant and its catalytic performances for

CO oxidation ［J］． Chemistry Select，2018，3 ( 43 ) :

12250-12257．

［11］ BULGAN G，TENG F，YAO W Q，et al． Effect of Ce

doping on the structure and catalytic activity of

La1－xCexCoO3 catalysts［J］．Acta Phys Chim Sin，2008，

24( 2) : 205-210．

［12］ DUAN X，SU C，MIAO J，et al． Insights into perovskite-

catalyzed peroxymonosulfate activation: Maneuverable

cobalt sites for promoted evolution of sulfate radicals

［J］．Appl Catal B-Environ，2018，220: 626-634．

［13］ GEBAＲA P，MAＲCIN J，KOＲVNEK I． Effect of

partial substitution of La by Ce on the nature of phase

transition in magnetocaloric La1－xCexFe11．2Co0．7Si1．1alloys［J］．J Electron Mater，2017，46( 11) : 6518-6522．

［14］ GHASDI M，ALAMDAＲI H，ＲOYEＲ S，et al． Electrical

and CO gas sensing properties of nanostructured

La1－xCexCoO3 perovskite prepared by activated reactive

synthesis ［J］． Sensor Actuat B-Chem，2011，156 ( 1 ) :

147-155．

［15］ XIAO P，ZHU J，LI H，et al． Effect of textural structure

on the catalytic performance of LaCoO3 for CO oxidation

［J］．ChemCatChem，2014，6( 6) : 1774-1781．

［16］ WANG H，ZHAO Z，XU，C M，et al． Simultaneous

removal of soot particles and NO from diesel engines

over LaBO3 perovskite-type oxides ［J］． J Phys Chem，

2008，29( 7) : 649-654．

( 责任编辑 刘钊)

653 中南民族大学学报( 自然科学版) 第 38 卷