Preparation and Methanol Decomposition Activity of Ruthenium Supported Ce-Doped Mesoporous TiO2 Oxid

JOURNAL OF RARE EARTHSVol. 23 ,No.3 , Jun. 2005 ,p. 340Preparation and Methanol Decomposition Activity of RutheniumSupported Ce- Doped Mesoporous TiO2 OxideZhang Xuehong(张雪红)2 ,Luo Laitao(罗来涛)* , Duan Zhanhui(段战辉y( I. Institute of Applied Chemistry , Nanchang University , Nanchang 330047 , China ; 2. Nanchang Instiute of ^Aero-nautical Technology , Nanchang 330034 , China )Abstract : Mesoporous TiO2-CeO2 mixed oxidd( m-TiO2-CeO2 ) were synthesized using n-cetylpyridinium chloride( Ci6PyCl )as astructure -directing agent under the neutral conditions and room temperature. The synthesized mesoporous samples were character-ized by FT-IR , XRD ,and N2 adsorption BET methods. The incorporation of Ce + ions into the channel wall improves the stabili-ty of the mesoporous structure obviously. After ruthenium being loaded by the impregnating method , the Ru particle strongly in-teracts with the mesoporous mixed supports. Although a part of the particles are possible to block the support pores，the catalyticactivity of ruthenium supported on the m-TiO2-CeO2 for methanol decomposition to carbon monoxide and hydrogen is significantlyhigher than that of ruthenium supported on m-TiO2. A synergitic efct between CeO2 and TiO2 was observed for promoting thecatalytic properties of Ru.Key words : mesoporous titanium oxide ; cerium ; ruthenium ; catalyst support ; methanol decomposition ; doped ; rare earthsCLC number :0643 .36 ;TQ134.1 Document code : AArticle ID : 1002 - 0721( 2005 )3 - 0340-05Mesoporous materials , for example silicic MCM-41 ,are required51. Various metals like nickel ，copper ,have been often employed as a catalyst support andplatinum and palladium supported over Al2O3 , SiO2 ,showed significant catalytic activity ，because the activeTiO2 ,ZO2 , CeO2 and synthetic clays are reported to bemetals can be highly dispersed in the characteristic poreeffective for the methanol decomposition to CO andstructure with high surface aret 11. Titania seems to beH[6].an active support , but the dispersion of Pd on its surfaceHere we report that mesoporous TiO2-CeO2 mixedis not highf 2]. For many applications , porous titania withoxide is an effective support of Ru which can be highlya large surface area is profitable. The successful synthe-dispersed in the pore structure by impregnating method.sis of stable mesoporous TiO2 involved the application ofExperimental .tetradecylphosphate surfactant as a template and removingit by caleination5 3]1.1 Preparation of TiO2/ CeO2 supportsHowever , the structure is probably destroyed afterMesoporous TiO2-CeO2 mixed oxide were synthe-the removal of the surfactant by thermal treat-ment. Sincesized as follows : 4 g of surfactant( n-cetylpyridiniumthermal stability is usually required as a catalyst support ,chloride , Ci6PyCl ) was dissolved in 20 ml ethyl alcoholit is necessary to obtain the thermally stable mesoporousabsolute( C2HsOH ), then 1. 94 g tetra-n-butyl titanateTiO2 powder. Earlier studies indicated that CeO2 oxides(TTIP ) and cerium nitrate( Ce( NO3 ): 6H2O ) werepossess better oxygen storage properties , improved ther-added at the same time. The mixture was stirred for 30mal resistance and catalytic activity at lower tempera-min at room temperature and then added 196 g de-ionizedtures , is a better additive4J. So far ,it has not been re-water slowly. This led to a precipitate.Mesityleneported that mesoporous CeO2-TiO2 mixed oxides can be( MES , 1.96 g ) was added to the solution. The resultantsynthesized by using n-cetylpyridinium chloride( C16Py-solid product in the solution was allowed to stand for 3 dCl)) as a template. For the probe reaction of methanolat 2中国煤化工were additionally treateddecomposition to carbon monoxide and hydrogen ，newineImoldm-3)foraboutHHCNMHGcatalysts being active at low temperatures below 473 K2 h w ennanve-te uieruid staunlity of the solid products .Received date :2004- 11- 15 ; revised date :2005 - 03 - 21Foundatign n; Zhang Xuehong( 1973- ), Female , Doctor candidate , LecturerCorrespondtg流thor( E-mail : luolaitao@ yahoo. com. cn)Zhang X H et al. Preparation and Methanol Decomposition Activity of m- TiO-CeO2341The products were dried at 373 K for 3 h. The meso-cm-1 is assigned as vibration spectrum of 0- H of wa-porous mixed oxide with different TiO2/CeO2 ratio wereter ,and the band of 2800 ~ 2900 cm-1 is correspondingsynthesized.to the vibration spectrum of C- H in alkyl chain. It1.2 Preparation of ruthenium catalystsshows that the surfactants are intercalated into hydrous ti-1% ruthenium was supported on commercial TiO2 ,tanium oxide. The band of 960 cm-1 belongs to the vi-mesoporous TiO2 or TiO2-CeO2 using 0.01 mol dm - 3 solu-bration spectrumof Ti-O. In the range of 1500~ 1200tion of ruthenium chloride by the impregration method.cm- 1 there are three new bands corresponding to the vi-After impregrating for 24 h , the samples were dried atbration of Ce - 0 after Ce doping. The intensity of these393 K ovemight and calcined in air at 673 K for 2 h.bands increases with the increase in Ce content of meso-The resulted samples were noted as 1% Ru/c-TiO2 ,1%porous TiO2-CeO2. These results indicate that all the Ce :Ru/m- Ti02 and 1% Ru/m-Ti02-CeO2 , respectively .in the mesoporous TiO2-CeO2 may be incorporated intc1.3 Catalytic activity measurementthe channel wall. From XRD pattems( Fig. 2 ), no char-Gas phase methanol decomposition was performed inacteristic peak of Ce2O3 or CeO2 at high angle appear af-a fixed-bed reactor under atmospheric pressure. The cat-ter Ce-doping. It is apparent that the d-spacing oalysts(0. 03 g) mixed with 1.0 g of quartz sand weremesostructure TiO2-CeO2 and the intensity of the peaksandwiched in a steel tube reactor of 6 mm i.d under the(2θ< 10°) are all varied , that is , with increasing Cereaction conditions. The samples were reduced in a flowcontent of mesoporous TiO2-CeO2 , they increase initiallyof 10% hydrogen diluted with nitrogen( flow rate , 10and then decrease. This result shows that doping of thecm' min-1 )for2 h at 673 K. After reduction , the cata-lysts were kept at the temperature of 453 , 473 , 493 ,proper amount Ce does not lead to the collapse of the513 , 533 and 553 K respectively under a nitrogen carriermesostructure , however the order arrangement will be de-( flow rate ,40 cm3 min - 1 ) and then methanol was pulsestroyed because of changing Ti - 0 framework with in-injected. The outlet gas was analyzed with an on line gaschromatograph ( GC102 ) equipped with a Porapark-Qcolumn ( 2 m ) and a thermal conductivity detector( TCD ), connected with a computer integrator system.The temperature of the column is 333 K. The catalyticactivity is assigned as conversion( % ) of methanol.1.4 Characterization|、<2)3Powder X- ray diffraction ( XRD ) patterns of the4)samples were recorded with D8 ADVNCE( Germany )28202diffractometer using nickel-filtered Cu Ka( 40 kV , 30Wavenumbers/102 cm"1mA ). The mesopore size distribution was determinedfrom the desorption isotherm of nitrogen obtained with ST-Fig.1 FT-IR spectrum of Ce-doped m-TiO22000( Bejing ). The BET surface areas and the total pore(1)TiwCeo ;( 2)TigCem ;( 3)TinCexo ;( 4)TigCexovolume of the samples were also determined( Table 1 ).The IR spectra of the samples were investigated on aTi..Ce。WQF-200 Fourier transform instrument ( Beijing ) withTi.CKBr wafer technique. Thermogravimetry analysis ( TG )were recorded by ZRY-2P ( Shanghai ) instrument in airTi,Ce,atmosphere with 10 K min - 1.中国煤化工TiCe2 Results and DiscussionfYHCNM H G,Ti.Ceg04060802.1 Structure characteristics of mesoporous TiO2-CeO2201(°)Fig. 1 shows the FT-IR spectra of Ce-doped m-Fig.2 XRD pttems of Ce-doped m-TiO2TiO2. The市熱据at about 3300 ~ 3500 cm-1 and 160042JOURNAL OF RARE EARTHS , Vol. 23 , No.3 , Jun .2005creasing Ce content sequentially. In addition , when theThe isotherm of sample TiooCeo shows a slow increase asCe content ≤30%，excluding low angle diffractionthe relative pressure pn,/ps 0.30~ 0.85 , that indicatespeak, XRD patterms shows a new peak at about 2θ =this sample has a broader pore-size distribution. The re-19° , which due to the formation of CeTi2( 0 ,0H》sults calculated( Fig.4 ) from the desorption isotherm al-( moloclinic crystal ) because of the strong interaction be-so prove this conclusion. The pore radius of TiooCeo is .tween Ti and Ce species. With increasing Ce content ,widely distributed from 4.95 to 10. 00 nm with a porethis peak weakens gradually. It is concluded that the in-volume of 0. 80 cm3. g-1. However , the isotherm oteraction of Ti - 0 band weaken gradually because of thesample TigoCe20 shows a ascent at a relative pressure PNincrease of Ce incorporating into TiO2 lttice. The rest ofp,0. 40~ 0.80 rapidly , the pore-size distibution alsoCe are likely to destroy the host material or block thechanges drastically after doping cerium. The pore size ofpore entrances , then make the intensity of the main smallthe mesoporous mixed oxide is sharply ditributed at 2.4angle diffraction peak weaken , and the order arrangementand 4.5 nm respectively and the pore volume is up to 1.of mesostructure decrease. When the content of Ce' +05 cm3 g-1. The BET surface area also increases fromreaches to 80%，the mesostructure is destroyed com-310.3 to 354.1 m2 g-1 , which is higher than that of thepletely.literature value( 200 m2 g-' )7].2.2 Surface textural properties of mesoporous TiO2-2.3 Methanol decompositionCeO2Methanol can be selectively decomposed to carbonA series of mesoporous TiO2-CeO2 mixed oxidesmonoxide and hydrogen on the whole series of rutheniumtemplated by C16PyCl are prepared under the neutral con-catalysts. For comparison ，methnol decomposition onditions and their textural properties are summarized inRu/c-TiO2 was studied too. No product suchTable 1.300↑The results of BET surface area show that surfaceareas and pore volume increase with the increase of thecontent of Ce'+ initially and then decrease. This indi-200|cates that doping of 20% cerium increase the surfacearea of TiO2 and inhibits the agglomeration process.100When the content of Ce3+ is above 20% , the surface11.C。area and pore volume decrease with increasing the contentofCe+. It might be due to a partial destruction of the).00.20.1.0ordering of the m-TiO2 or due to block of the pore en-trances .Px/P,Fig. 3 shows the N2 desorption isotherms of the TiooFig.3 Nitrogen desorption isotherm of mesoporous mixed oxideCeo and TigoCe2o samples . The isotherm of TigoCe2o showsa fast increase as the relative pressure pn,/ Ps higher than0.20-0.4. Such isotherm exhibits a profile between type IandtypeIV，thetypicalmesoporous百0.1S-material MCM - 4 1 profile with pore size of 2.5 nm.0.10Table 1 Synthesis conditions and textural properties of mesoporousTiO2-CeO2亏0.05-TigCe2Ce' + content/BET surfacePore volume/Samplesarea(m2 g1) (cm2 g~1)0.00-●TignCeTiz2Ceso8C193.80.46中国煤化工15 20 25 30TisoCero0218.00.52TisoCeso261.20.61MHCNMHG'mFig.4 Pore size distributions of samplesTinoCeso306.21.00as methane was detected under the reaction conditions.TigoCezo354.11.05The concession( % ) of methanol were plotted against theTiuoCen310.30.80reaction temperature from 453 to 553 K( Fig.5). WithZhang X H et al. Preparation and Methanol Decompoition Activity of m- TiO-CeO2343increasing the reaction temperature , the catalytic activityThen activation energy of catalysts for methanol decompo-of all catalysts is found to increase. The activity of Ru/sition can be obtained from the slope in the line of lnm-Ti02 at 453~ 553 K is higher than that for Ru/c-[ p°lr(1-x)-1]1~ T-1. The apparent activation en-TiO2 , that is , the methanol conversion at 453 K areergies calculated fron the data in Fig.6 are 13.57 ,17.55.78% and 52.05% , the methanol conversion at 55327 and 20.31 kJ} mol- 1 for Ru/m-TiO2-CeO2 , Ru/m-TiO2 and Ru/c-TiO2 catalysts respectively. The highestK are 92.26% and 80. 46% , respectively , which due torates as well as lowest activation energies are observedthe Ru particles with better distribution on the high sur-over Ru/m-TiO2-CeO2.face area m-TiOf( The BET surface area of m-TiO2 and c-Hydrogen adsorption on the ruthenium catalysts wasTiO2 uncalcined is 310.3 and 1.1 m? g-' respectively ).performed at room temperature on catalysts reduced withHowever , the difference of the BET surface area are hun-hydrogen at 673 K. The surface area of Ru was calculat-dredfold ,but not of the activity , the surface area is noted from the amount of H2 irreversibly adsorbed , assumingthe only reason for catalytic activity.the site density of Ru as 0.06 nm2 atom-1 and the stoi-Compared to the mesoporous Ru/ m-TiO2 , the meso-chiometry of one hydrogen atom per Ru atom exposed onporous Ru/m-Ti0O2-CeOL the Ce content is 20% ) mixedthe surface 12]. The results are given in Table 2. The Ruoxides are found to be efficient catalysts for methanol de-surface area for Ru/m-TiO2-CeO2is 1.41 m2 g-' cat-composition. The activity of the catalysts decreases in thewhich is higher than that for Ru/m-Ti02 0.12 m2 g-lfollowing order : Ru/ m-TiO2-CeO2 > Ru/m-Ti02> Ru/c-cat - I ) significantly , so the catalytic activity increases.TiO2. It is concluded that Ce-doping facilitate the forma--58.5tion of very small ruthenium particles and their better dis--59.0{Ru/m-TiO2-CeO2tributions on the surface of the mesoporous mixed oxidesupports. According to the model of the first-order reac-芒-s9.5.Ru/c-TiO,tion kinetics proposed previously89] :是'-60.04hK=[ r0(273RW )]xlr(1-x)-1 r°=( T)Ru/m-TiO,hi : rate constant ; K : adsorption equilibrium constant ;-60.5-F0 :flow rate of carrier at stantard state ; W : catalyst-61.0weight ; x : conversion1.6 . 1.7 .1.8 1.920212.2 2.3associated with Arrhenius formuld 10J]:r/103 K:'Ink= -( E。/RT )+ lnAFig.6 Arrhenius plot of rate of methanol decomposition overh :rate constant ; E。: activation energy ; A : frequencyruthenium supported catalystsTable 2 Properties of catalystsfactor.So the follow equation is deduced :CatalystBET suface area/ H acdobed/Ru suface area/(m2 g')(molg-' cat-')(m2 g' citr')100Ru/c-TiO20.950.0100.0990Ru/m-TiO20.0140.12Ru/m-Ti02-CeO2 221.20.181.418070References :十1% Eu/c-TiO,60+1% Ru/m-TiO,[1 ] Mahendra K P, Yuichi I, Koji K, et al.Catalytic十1% Ru/m-TiO2-CcO2methanol decomposition over palladium deposited on ther-460 480 500520 540 560中国煤化工im oxide[J]. 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Deternination of sufaceordering lengths and semicrsalline framework[J] Chem.of the Ni supported catalyst by pulsed chromatography[ J].Mater. ,1999 ,11 :2813.Chemistry , 1981 ,1 :31.Effect Factors on Synthesis of CeO2 Nanoparticle by Precipitation MethodQiu Guanzhou, Song Xiaolan* , Qu Peng , Yang Zhenhua, Wu Xuelan, Wang Haibo ( School ofResources Processing and Bioengineering , Central South University , Changsha 410083 , China )Abstract : High pure activing CeO2 nanoparticle werewashing , dehydrating and drying ,at 300 C for 1 h ob-successfully synthesized by chemical preciptationtained from reaction of 0.1 mot L-'( NH4 )2C0; H20method. The effect factors such as reaction temperature ，solution as precipitator and 0.1 mol L-1 Ce( NO3 ); .reaction time ，mechanical stirring velocity , surfactant ,6H2O according to chemical measure ratio with 0. 4%calcinations temperature and calcinations time on grainPEG4000 as surfactant. The optimizing conditions of resize or relative density of CeO2 nanoparticle are investi-action are 40 C reaction temperature , 10 min reactiongated, and optimizing conditions were obtained. Thetime, 800 r min~ mechanical stirring velocity. Theproperties of CeO2 nanoparticle were characterized byproperties of CeO2 nanoparticle are of cubic crystal systemXRD ,DTA/TG , TEM , BET surface area , N2 isothermand space group ,about 5 nm average grain size , about 20adsorption and desorption , BJH desorption pore size dis-nm particle size , 140.61 m2 g-1 BET surface area ,5~tribution and impurity content analysis. The results show15 nm pore size distribution and 9.3 nm maximum porethat CeO2 nanoparticle are formed entirely by heating thesize , not lower than 99.97% purity.precursor Cef CO3 ); H2O , after water washing , ethanolKey words : CeO2 nanoparticle ; precipitation method ; efect factors ; rare earths(SeeJ. Chin. RE. Soe. ( in Chin. ),2005 ,23(3):321 for full text)中国煤化工MHCNMHG.