Chem.Res.Chin.Univ.,2016,32(6),1005--1009 doi:10.1007/s40242—016—6130.6 Effect of Zr Addition on Catalytic Performance of Cu..Zn..AI Oxides for CO2 Hydr0genatiOn to Methanol BEN Shunge,YUAN Fulong and ZHU Yujun KeyLaboratory fFunctoionalInorganicMaterial Chemistry(tteilongfiang University),Ministy rofEducanon。 School ofChemistryandMaterials,Heilongfiang University,Harbin 150080. R.China Abstract A series of 50%CuO一25%Zno一25%Al(Zr、oxide catalysts was synthesized by a reverse co—precipiattion method and characterized by XRD,N2 adsorption-desorption,H2.TPRH2-TPD and C02-TPD,and used as catalyst ,for C02 hydrogenation to methanol under mild conditions(200--260。C and 1—3 MPa).Consequentl ̄H2.TPR ex. hibited that the dispersed CuO species increased、 th the zirconium contentwhile the H2-TPD showed that small .amount of zlrcoma can mcrease the H2 desorption amount.As a result,Cat-2 and Cat.3 exhibited an enhanced H2-spillover effect,the most H2 desorption mounta,which showed an optimum activity of about 7%methano1 yield. Keywords Carbon dioxide;Reverse co-precipitation;Methanol;Catalytic hydrogenation;Copper based catalyst 1 Introduction C02 is the most famous greenhouse gas,and its emission quantity has enlarged one time amongst last 60 years with the development of industry and economic scalet .tion property on Cu/Zn0 catalyst[8,24-27]In additiOn.Yesear- .chers found that the strength and amount of CO,and}工,ad. sorption on Cu-Zn oxides surface had a great influence on catalytic actiitvy[ 。一 。】 Obviously,synthetic method andthe property of catalysts exhibited signiicafnt influence on their reaction activity In order to gain more detailed information about meta1 additive nfiluence on catalyst surNce adsorption conditiona series of ,Now i,t s iextremely urgent for people to explore methods to utilize the excesNve CO2 Methanol synthesis through CO2 hydrogenation is a promising one,which could not only dimimsh greenhouse gas.but also has a wide range ofapplications as raw material to synthesis valuable chemicals[4,5JRecemly,researches have .50%CuO-25%ZnO-25%-Al(Zr)oxides catalysts was synthe.. sized through a convenient reverse co-precipitation method. Their catalytic activities toward CO.hydrogenation to metha- no1 havebeentested. ocused their atftention on the catalyst synthesis and modifica- tion for C0,hydrogenation to methanol[。一 …. Normally,noble metal catalysts and non-noble metal ca- talysts are mainly apphed in this reaction.For example,noble metal catalyst were mainly used as fndamentalu catalyst for 2 Experimental 2.1 Catalyst Preparation A series of 50%CuO.25%Zno-25%A1rZr1 oxides catalysts was prepared by the reverse co-precipitation methodand the ,mechanistic study in methanol synthesis reaction(MSR)t“, Nevertheless catalysts such as Pt and Pd exhibited a low em. ciency for methanol production because their active sites were easily poisoned during reactiont .Currently,Cu and Zn were metal oxide compositions of CuO and ZnO of 50%and 25% have been used according to the literature[21,31,32]hl brief,7.91 .recognized as the most effective activity component because they cai/generate H,一spillover effect by metal-oxide intemc— tion[ , 一 ]Howeverthe eficifency of copper-based catlysta ,g ofCu(NO3)2’3H2O,4.76 g ofZn(NO3)2。6H2O,andAl O3)3- 9H20(9.58,7.19,4.79,2.40 g),Zr(NO3)4。5H2o(1 13,2.27, 3.40 4.54 g1 as raw materials were dissolved in 1OO mL of distilled water and the mass fractions of Cu0.still remains a question in MSRt 一 In order to improve the activity of Cu-Zn oxides,diferent additives like Zr,Ga and modified synthesis method were used.Wang et a1.L22J prepared Zn0 and Cu/ZnO/A1203 catalysts by adding CO2 during the [(1 )A1203+xZrO2(x=0,0.25,O.5,0.75,1)】were kept at 50%, 25%and 25%.respectively nle precursor solution was added dropwisely to 0.1 mol/L Na,CO solution under stirring111e .co-precipiattion aging step to give a higher activity for MSR(200--260。C、.Ladera et al t 1 prepared Ga-doped Cu/ZnO/ZrO々catalysts.which increased the abundance of surfaceCuandtheamount ofmetallicCu withGa,O11oading. pH value of the solution was maintained at about 10.After precipitation the catalyst precursor was sti仃ed for another 1 lL henftiltered.washedwithdistilledwaterfor severaltimes 11le moreover,phase transformation of zirconia from tetragoual to monoclinic showed relative impact on catalyst surface adsorp. precipiatte was dried at 80。C ovemight nd faitrther calcined t a400。C for 2 h.nIe synthesized catalysts were denoted aS Corresponding authors.E—mail:yujunzhu@hlju.edu.cn;fluongyuan2000@yahoo.corn ReceivedApril 5,2016;accepted August 25,2016. Supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars,Ministry of Education of China(No.2013-1792)andtheMinistry ofHumanResourcesand Social Security,China(No.2013—277). ◎Jilin University,The Editorial Department of Chemical Research in Chinese Universities and Springer-Verlag GmbH Chem.Res.Chin.Univ 、,ol-32 Cat-n(n=1—5、according to x from 0 to 1 2.2 Characterization Techniques 10。C/min 2.3 Catalytic Activity Evaluation Activity measurements for CO,hydrogenation were car. X-ray difraction(XRD)patterns were recorded using CuKa adiration on a D AX.3B X.ray Difireatome. ried out n ia ifxed.bed reacton 0.5 g of catalyst(40--60 mesh) was placed in a staimess steel tube reactor.First.the catalyst was reducedin pureH,at aflow-rate of 30 mL/min underat. mosphere pressure.The reduction temperatre was iuncreased rom 20。C to 300。C atf a rate of 10。C/min.Then.the sample was cooledto roomtemperatureunderN2flow at aflow-rate of 20 mL/min.Aftr reducteion C0,hydrogenation process was performed under reaction condiitons of 200—260。C.3Ⅳ 乱 ter(Rigaku Co.).BET speciifc surface area wfls obtlned by aN2-adsorption.desor0tion with a Micrometritics TriStar 3020 instnunent. Temperature—programmed reduction with H2(H2一TPR) were carried outwithflfu11 automaticinstrttrnent(XQTP.5080. China).Briefly,20 mg of catalyst was calclued at 100。C for 1 h under oxygen stream(30 mL/min).After being cooled to roomtemperature.the samplewasheatedfrom 50。Cto 500。C tarateof1O。C/mian. Temperature-programmed desorption experiments of H2/CO2 molr aratio of 3:1 and GHSV(gas hourly space velocity) of 6000 mL’g ‘h- .Products were quantitatively analyzed onlinewith a gas chromatograph(GC)equippedwith athermal conductivity detector(TDX.0 1 column)and a ̄llle ionization detector(Propark.O column). CO2(CO2一TPD)or H2(}I2一TPD)were preformed almost the same as H2.TPR measurement.100 mg of catalyst was mountedina quartztube and reducedunder 1O%H々.N々flow at 300。C.then cooled downto roomtemperature.Afterthat.pure C0,OrH,wasintroduced at a rate of20mL/minfor 1 h.Then 3 Results and Discussion he compositiTons ofthe catalysts are shown in Table 1, which arc close to the theoretical ones in the mother the catalyst was flushed itwh He flow(30 mL/min)to remove physisorbed CO2 or H2 at room temperature.Finally,the sam- ple was heated from 50。C to 800 or 300。C at fl ramp of solutions. Table 1 Composition and physical parameters of calcined Cat-n catalysts 24。,35。were assigned to he tcrysalt face 9f(003),(006),(009) 3.1 XRD Measurement itwh layer structure ofhydrotalcite-tvpet 1.Wih the tncreaise of zirconium content,the peak intensiites decayed gradually among Cat =2—5 ,while no Deak at 60。was observed for The XRD patterns of he tprecrsorus of Cat-n(n=1—5、are shown in Fig.1(A).For Cat-1,the diracftion peaks at 20 12。, Cat一5[Fig.1(A)】,which demonsrtated that the layer structure had been destroyed by the excess doping ofzirconiunl and all morphous structure was faormedt”JThe)(RD paRerns ofthe .calcined smplaes are shown in Fig.1(B).For Cat— =1—4), the difraction peaks of CuO at 20 35.6。and 38.7。were ob. served.and the peak at 31.7。with a weak intnsity was as.e signedtoZnO.However,theintensities ofthediffractionpeaks ofCat.5weremuchweaker.ForalltheCat.n(n=l一5、catalysts. no diffractionpeaks ofzirconiumwas observed whichm'lphed he existetnce of amorphous or microcrystal zirconium oxidet。, , Zirconium content showed a negligible impact on BET surface area(120—126 m /g1 of Cat-n(n=l—41.while Cat.5 exhibited a mininluln surface area of 99 m /g due to the complete substitution ofAl bv Zr【34,35J. 3.2 H2一TPR Results TPR measurement were carried out to understand the reducibility and copper oxides of the Cat 20/(。) =1—5、and the results are shown in Fig.2.The reduction profiles were the Fig.1 XRD patterns of precursors(A)and calcined result of a complex overlapping of several reduction processes. For ZnO and ZrO2 no reduction pedk was observed under catalysts(B) .Cat-l;b.Cat-2;c.Cat-3; Cat-4;e.Cat-5. experimental condition(50--500。C、.so all he tpeaks should e bNo.6 BENShunge etal 1007 contributed to the reduction of copper oxide species.Generally, hte reduction Deak of bulk CuO appears at nearly 350。C and will shifttolowtemperaturewiththeincreaseinthedispersion of copper species.In order to obtain detailed information of active copper species,the peaks were deconvoluted and fitted to the highly dispersed Cu0.dispersed CuO cluster on catalyst surface and bulk CuO species according to the increase of reduction temperature[8,36,37】,which were denoted as , and y peaks.respectively.111e resuRs are displayed in le S1(see hte Electronic Supplementary Materila of this paper).Cat.1 showed a small peakatabout190。C.whichwastooweakto be discemed.nle a peak of Cat-2 and Cat.3 appeared at 209 nad 21 7。C.respectively.HE consumption of a peak increased gradually from Cat-1 to Cat-3(1.5,12.7,and 34.8 ̄unol/g for Cat-1,Cat-2 and Cat-3,respectively). peak posiiton of reduciton peak of Cat-n(n=1—3、demonstratde a negligible change(240--243。C1.and hte H2 consumption decreased from 55.8 ̄trnol/g to 37.0 Ixmol/g with the increase in zirconium content.For Cat_4 and Cat-5 two peaks assigned to a and were observed at 210 and 235。C,wihtout reduction of bulk CuO speciest 】.Furthermore.the H,consumption of a peak nicreasedto 46.7 and 66.4 lmaol/g for Cat-4 and Cat.5,respec. tively.Generally,H2 consumption of a peak increased greatly from 1.5/nnoYg(Cat一1)to 66.4/nnol/g(Cat-5)with the nicrease of zirconium content.This result indicates that the amount of hte highly dispersed CuO species shows a pronounced increased with the increase in zirconium content.It is noticed htat the totla amount ofthe highly dispersed CuO(a)and ids- eprsed Cu ̄f1)species nicrease wiht hte zirconium contnet for Cat. =1—5),whichindicatethattheadditionofZrfavorsthe dispersion ofthe reducible CuO species and the improvement of reduction ability[39J.The v reduction peak ascribed to bulk CuO disappeared completely for Cat-4 and Cat-5,which is consistent iwth the result fromⅪ .and illustrates the reduci- ble copper specieshavealteredwiththe addition ofZr. Temperature/ ̄C Fig.2 II2-TPR proflies of the calcined catalysts a.Cat-l;b.Cat-2:c.Cat-3; Cat-4;8.Cat-5. 3.3 II2・TPD Analysis Fig.3 shows the H2.TPD profiles of Cat-n =1—5),which demonstrate the H2 adsorption behavior on reduced catalyst. hTe desorption peaks were analyzed with the deconvolution obtained by iftnig Gaussina epaks(Fig.3 nad Table s2.see hte Electronic Supplementary Material of this paper).Three de- sorptionDe kSwere attributedto differenthydrogen adsorption states on the surface of lal Cat =1—5)smaples.The 1ow temperature(141--251。C)peak(a)represent hte desorption of atomic hydrogen on surface Cu sites.thereafter the de Deak at 424—469。c peak)and 482—611。c(r peak)were as- cfibed to the diferent sort of strongly absorbed hydrogen on hte Zn0 surfacel , J.Among al1 the Cat =1—51 catalysts, Cat-2 exhibits hte largest a desorption peak area(633), peak area(3688)and total peak area(5039),which mea/1s that a stronger spillover effect caused by the Cu.Zn oxides interaction could be generated on the surface ofCat.2 compared with the other samples[40,41】. Tempcrature/ ̄C Fig.3 H2-TPD profiles of the reduced catalysts 口.Cat-1;b.Cat-2;G.Cat-3; Cat一4;8.Cat-5. 3.4 C02-TPD Results The CO2-1PD profiles of Cat. =1—51 ale shown in Fig.4.nle :ka located in the range of 25—25O。C and gra- dually became widen.Al1 the profiles were deconvoluted into three Gaussina peaks,the a peak(64—75。c), peak f83一l10。C1 and 7 peak(112—161。C1 for diferent basic sitest42J.n amounts ofthe basic sites ofdiferent types were calculated and shown in T{ le S3(see the Electronic Supple. mentaryMaterila ofthispaper).Wihttheadddionofzirconium, hte position of three CO,desorption peaks exhibited a扛end towards hi temperature.Peak a shiftedto highertemperature rfom 64。C to 75。C with the increase in zirconium content, meanwhile,Cat-3 exhibited the maximum number of weak basic sites(47.7 pmol/g). and peak posiiton displayed a similarvariaitontnedency(from 83。Cto 110。C and 112。C to 161。C1,while the number of basic sites of Cat.3(41.7 prnol/g)appeared to be superiority among Cat-n(n=1—5).Ap- parenfly,theZr contnetexhibietdagreatinfluence onbasic site distribution.Cat.3 showed hte largest total basic amount(120.1  ̄moYg). Temperature/ ̄C Fig.4 CO2-TPD profiles of the reduced catalysts 口.Cat-l;b.Cat-2;0.Cat-3; Cat-4:8.Cat-5. 1008 Chem.Res.Chin.Ulliv 、,01.32 ofCat.2 was maintained within 48 Fig.S1 see the Electronic 3.5 Activity Evaluation The MSR reaction is arl exothermic reaction which favors at low temperature.However,activation of CO2 needs elevated Supplementary Material ofthis paper) H2.TPR measurement exhibited that the Cat-n(n=1—51 contained different types ofactive copper species,and the total amount of dispersed CuO species was increased with increa— 一 一宣0IsJa言00 u 一 v}王0n墨u 9 IA 0 _【0∞ sing zirconium content.On the other hand.H2-邢result ex. thermal condition In Fig.5(A),it was obviously found that C02 conversion increased with the reaction temperature.For exam. pie.CO,conversion increased from 6.3%to 18.8%for Cat.2. hinted that doping of small amount zirconia enhanced the 加 8 4 O ∞ ∞ ∞ 加 0 when the temperatrue increased from 200。C to 260。C.The increment of CO,conversion gradually got approach to the reaction balance when temperature increased to 240。C.Con. trast to the influence of temperature on CO,conversion.a completely opposite influence of temperature on methanol selectivity was observed,which exhibited a lower methanol selectivity at high temperatrue and a higher methanol selectivi. tv at low temperature.for example.from 79 6%to 34 6%for Cat-2[Fig.5(B)】.In the range of200--240。C,、Ⅳim hte increase of reaction temperatttre,the yield of methanol increased gradu. ally[Fig.5(C)1.At 240。C,Cat-2 achieved hte best yield(7_2%), which decreased by the fruther increase oftemperature(6.5%at 260。C、.Generally,Cat-2 showed the best methanol yield at 240。C and Cat.5 displayed the weakest activity among all the Cat-n catalvsts.The stability results exhibited that hte activity 200 220 240 260 Temperature/ ̄C Temperature/'C 0 士 U 0 里 . Temperature/ ̄C Fig.5 Influence of temperature on C02 conver- sion(A),CH3OH selectivity(B),and CHsOH yield(C) 一Cat-l;口Cat-2 ●Cat-3;圈Cat-4;豳Cat-5. H2.spillover effect exceedingly,in which Cat-2 showed the 1argest H々desorption amount However,CO2-TPD exhibited htatthe contniuous adding ofzirconia elevatedthe strengthand amount of surfacebasic sites in Cat. r =3—51.In shortwords, the adsorption ability of H2 is more important to catalyst acti. vi Both Cat.2 and Cat-3 exhibited high yield of methanol in hte temperatrue seope of 2O0—26O。C.which were attributed to the comprehensive actions of dispersed CuO species,high H2 desorption amount and large amount of surface basic sites derivedfromZraddition. 4 Conclusions Cu.Zn-Al(Zr)oxide catlaysts were synthesized through reverse co.precipitation method.Cat-2 and Cat-3 showed better catalytic perfornlance for methanol synthesis.and 7.2%and 6.5%yield were obtained under 3 MPa.240。C condition.re— spectively. is is mainly because Cat-2 showed the 1argest amount of H,adsorption while Cat 3 showed a high content of basic sites to adsorb CO,.Consequently,the better activity should be attributed to hte comprehensive actions. 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