Research Article Effect of Copper Nanoparticles Dispersion ...

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2013 Article ID 629375 6 pageshttpdxdoiorg1011552013629375

Research ArticleEffect of Copper Nanoparticles Dispersion on CatalyticPerformance of CuSiO2 Catalyst for Hydrogenation ofDimethyl Oxalate to Ethylene Glycol

Yajing Zhang Na Zheng Kangjun Wang Sujuan Zhang and Jing Wu

College of Chemical Engineering Shenyang University of Chemical Technology Shenyang 110142 China

Correspondence should be addressed to Jing Wu wujing7275163com

Received 14 January 2013 Accepted 10 February 2013

Academic Editor Guo Gao

Copyright copy 2013 Yajing Zhang et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

CuSiO2catalysts for the synthesis of ethylene glycol (EG) from hydrogenation of dimethyl oxalate (DMO) were prepared by

ammonia-evaporation and sol-gel methods respectively The structure size of copper nanoparticles copper dispersion and thesurface chemical states were investigated by X-ray diffraction (XRD) transmission electron microscopy (TEM) temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) and N

2adsorption It is found the structures and

catalytic performances of the catalysts were highly affected by the preparation method The catalyst prepared by sol-gel methodhad smaller average size of copper nanoparticles (about 3-4 nm) better copper dispersion higher Cu+C0 ratio and larger BETsurface area and higher DMO conversion and EG selectivity under the optimized reaction conditions

1 Introduction

Ethylene glycol (EG) is widely used as solvent antifreezerpolyester fibers and precursors in lubricant and polyestermanufacture [1] At present a universal industrial approachto EG is the direct hydrate from ethylene oxide obtained byoxidation of ethylene with air or oxygen while the ethylenecomes from the petroleum cracking process However aspetroleum resources shrink and the demand for EG con-stantly increases the synthesis of EG from syngas attractsconsiderable attention because it provided an alternative non-petroleum route to produce EG [2] Two steps are includedin this route first the coupling of CO with methanol tooxalates second hydrogenation of oxalates to EG [3 4]Considerable efforts have been focused on the second stepThe hydrogenation process can be completed by both homo-geneous and heterogeneous catalysis reactions Comparedwith homogeneous hydrogenation heterogeneous processhas advantages of easy to separate product and low costTherefore much attention has been focused investigationon the heterogeneous catalysts [5ndash7] It is known thathydrogenolysis of monoalkyl ester to alcohol has been in

successful industrial operation and the copper-based cata-lysts are suitable for the process [8] However compared withhydrogenolysis of monoalkyl ester to alcohol hydrogenolysisof dialkyl ester is more difficult considering that this selectivehydrogenation has to be sufficient to reduce the dialkyl esterand avoid overhydrogenolysis of glycol to ethanol and otherby-products [9 10]

Previous studies have shown that the copper loading Nispecies doping preparation temperature and support acidityhave an influence on texture structure and catalytic perfor-mance of the catalyst [11 12] To achieve high catalytic activityit is important to disperse fine metal particles on the surfaceof a support even at higher metal loading [13] Althoughvarious preparation methods have been reported includ-ing sol-gel ammonia-evaporation deposition-precipitationimpregnation and coprecipitation [14ndash16] few reports focuson the influence of the copper nanoparticles dispersion on theCuSiO

2catalysts for hydrogenation of DMO to EG

In the present study for comparison purpose we adoptedthe sol-gel and ammonia-evaporation methods to prepareCuSiO

2catalysts with same Cu loadings and evaluate their

catalytic properties for the hydrogenolysis of DMO to EG

2 Journal of Nanomaterials

respectively In an attempt to understand the effect of Cunanoparticles dispersion andpreparationmethods on the cat-alyst structure and catalytic performance we characterizedthese catalysts by means of the techniques such as nitrogenphysisorption X-ray diffraction (XRD) X-ray photoelec-tron spectroscopy (XPS) temperature-programmed reduc-tion (TPR) and transmission electron microscopy (TEM)This work not only can provide a research foundation for thedevelopment of industrial catalysts for the synthesis of EG viaa nonpetroleum route but also can provide some deep insightfor the design of high active copper-based catalysts for otherreactions

2 Experimental Section

21 Catalyst Preparation All the reagents used are analyt-ically pure CuSiO

2catalysts were prepared by ammonia-

evaporation and sol-gelmethods with the samenominal cop-per loading of 30wt (CuO(CuO + SiO

2)) respectivelyThe

ammonia-evaporation method was carried out as followsAt room temperature 136 g Cu(NO

3)2sdot3H2O (Sinopharm

Chemical Reagent Ltd) was dissolved in 150mL of deionizedwater 42mL of 28 ammonia aqueous solution (SinopharmChemical Reagent Ltd) was added and stirred for 30minThen 420 g of silica sol (JA-25 Qingdao Haiyang ChemicalLtd) was added to the copper ammonia complex solutionand the initial pH of the suspension was 11-12The suspensionwas stirred for another 3 h Then the suspension was heatedto 363K and kept at this temperature for the evaporationof ammonia The evaporation process was not terminateduntil the pH decreased gradually to 6-7 Then the productwas filtered washed by deionized water for several times anddried at 393K for 12 h Then the product was calcined in amuffle oven at 723K for 4 h After calcination the catalyst waspelletized crushed and sieved to 20ndash40 mesh The catalystwas referred to as CuSiO

2-AE

The sol-gel method was carried out as follows Tet-raethoxysilane (TEOS Sinopharm Chemical Reagent LtdChina) and copper nitrate trihydrate were used as the silicaand copper sources respectively The mixture of ethanol(C2H5OH) and water (H

2O) was used as solvent the mass

ratio of TEOSC2H5OHH

2O was 111 The mixture was

stirred homogeneously and kept at room temperature for20 h for gelation Then the product was filtered washed bydeionized water for several times and dried at 393K for 12 hThen the product was calcined in a muffle oven at 723K for4 h After calcination the catalyst was pelletized crushedsieved to 20ndash40 mesh The catalyst is referred to as CuSiO

2-

SG

22 Catalyst Characterization XRDmeasurementswere per-formed on a Bruker D8 X-ray diffractometer with Cu-K120572radiation (120582 = 154156 A) at a scan rate of 4∘minminus1 at 45 kVand 40mA

BET surface areas were measured by N2adsorption at

77K using a Micromeritics SSA-4000 instrument Beforemeasurements samples were degassed under vacuum at298K for 3 h

The XPS measurements were performed on a Perkin-Elmer PHI 5000 ESCA photoelectron spectrometer using anAl K120572 (h120584 = 1 4866 eV) source The binding energies of theelements on the surfaces of the catalysts were corrected byusing the carbon C1s value 285 eV as an internal standard

TEM images were obtained on a JEOL JEM 2010 trans-mission electron microscope with accelerating voltage of200 kV

H2-TPR was also conducted to examine the catalyst

reducibility 50mg of the catalyst was heated in He at 673Kfor 60min followed by cooling to room temperature Thetemperature was then raised in 50mLmin of 10 H

2Ar

using a ramp rate of 10 Kmin to 823K H2consumption was

detected using TCD

23 Catalyst Testing Activity and selectivity measurementsfor DMO hydrogenation to EG were carried out in acontinuous-flow fixed-bed reactor made of stainless steel(id = 7mm) 12 g catalyst was placed into the reactor Thereaction pressure was 20MPa and the reaction temperatureis 453K Prior to the catalytic measurements the catalyst wasreduced in a streamof 10H

2N2at 553K for 4 h under atmo-

spheric pressure After cooling to the reaction temperaturethe catalyst bed was fed with 10 DMO in methanol and H

2

and H2DMO is 80 (molmol) The DMO in methanol was

supplied by a syringe pump (SSI) vaporized and mixed withthe H

2feed in an electrical heated stainless steel preheater

at 443K The hydrogen feed was controlled by the massflow controllers The exit gases were cooled down to roomtemperature in a water-cooled condenser The liquid productwas collected and analyzed by gas chromatograph (BeijingBenfenruili Ltd 3420) equipped with an FID detector

3 Results and Discussion

31 Performance of Different CuSiO2Catalysts The catalytic

properties for DMO hydrogenation to EG over the CuSiO2-

AE and CuSiO2-SG catalysts were tested For the synthesis

process of EG from hydrogenation of DMO it can beexpressed by the following reactions [17]

(COOCH3)

2+H2997888rarr CH

2OHCOOCH

3+ CH

3OH (1)

CH2OHCOOCH

3+H2997888rarr (CH

2OH)2+ CH

3OH (2)

(CH2OH)2+H2997888rarr C

2H5OH +H

2O (3)

(CH2OH)2+ C2H5OH 997888rarr HOCH

2(OH)C

2H5+H2O(4)

During reaction process first methyl glycolate (MG) isproduced by hydrogenation of DMO then further hydro-genation of MG to EG while EG can dehydrate to ethanol(ET) At certain conditions EG and ET can dehydrate to12-butanol (BDO) MG is known as a partial hydrogenationproduct while ET and BDO are called the excess hydro-genation products The EG is a major product and theother products are side products in our experiments Theconversion of DMO the selectivity of EG and the yieldof EG on CuSiO

2are shown in Table 1 Compared with

Journal of Nanomaterials 3

Table 1The catalytic activities of the CuSiO2 catalysts prepared bydifferent methods

Catalyst 119883DMO 119878EG 119884EGCuSiO2-AE 98 96 941CuSiO2-SG 96 93 893Reaction conditions T = 353K P = 20MPa H2DMO = 80 (molmol)LHSV = 06 hminus1

CuSiO2-AE catalyst the CuSiO

2-SG catalyst exhibits higher

activity Conversion of DMO and selectivity of 98 and96 are obtained on CuSiO

2-SG catalyst at optimal reaction

conditions It is well known that the catalytic performance ofthe CuSiO

2catalysts is highly dependent on structure size

and dispersion of copper species and surface chemical statesof the catalysts The different catalytic performance of thetwo CuSiO

2catalysts could be resulted from their different

structures And further discussion will be carried out in thefollowing parts In addition compared with other copper-based catalysts prepared various methods the CuSiO

2-SG

catalyst here also exhibits equal or higher activity [2 10 11]Under the reaction temperature of 453K reaction pres-

sure of 2 and Mpa and H2DMO molar ratio of 80 the

effect of different liquid hourly space velocity (LHSV) onthe performance of the CuSiO

2catalysts is investigated and

the results are shown in Figure 1 It can be clearly seen thatconversion of DMO decreases gradually while the selectivityof EG first increases and then decreases with increasingLHSV over both CuSiO

2catalystsThe EG selectivity of each

catalyst reaches themaximumwhen the LHSV is 06 hminus1Thischanging trend of the selectivity can be understood from thepoint of view of residence time When the LHSV is lowera longer residence time for reactants is obtained resultingin overhydrogenation of EG and the production of ET andBDO and the EG selectivity is consequently lower Whileunder higher LHSV the residence time is shorter leading topartial hydrogenation of DMO and the production of MGbut not EG and therefore the selectivity is also lower Bycomparison it is found that both of the conversion of DMOand the selectivity for EG over the CuSiO

2-SG catalyst are

greater than those of the CuSiO2-AE catalysts

32 The Characterization of the CuSiO2Catalysts

321 Textural Properties andMorphology Figure 2 shows theXRD patterns of the reduced CuSiO

2catalysts prepared with

different methods The strong and sharp peaks observed (seeFigure 2) confirm that the catalysts are all well crystallizedFor CuSiO

2-AE the diffraction peaks appearing at 433∘

504∘ and 741∘ can be indexed to Cu phase (JCPDS 85-1326)and the broad and diffuse diffraction peak at around 217∘can be attributed to amorphous silica phase (JCPDS 88-1535)as shown in Figure 2 It is also found the diffraction peaksintensities of the CuSiO

2-SG catalyst are much weaker than

those of CuSiO2-AE which implies the copper dispersion of

the CuSiO2-SG catalyst is higher than that of CuSiO

2-AE

The physicochemical properties of the calcined catalystsare summarized in Table 2 It is clearly shown in Table 2 that

100

90

80

70

60

50

40

3004 06 08 1 12 14 16

Con

vers

ion

sele

ctiv

ity (

)

LHSV (hminus1)

DMO conversion over CuSiO2-AE

EG selectivity over CuSiO2-SGEG selectivity over CuSiO2-AE

DMO conversion over CuSiO2-SG

Figure 1 Effects of DMO LHSV on catalytic performances ofCuSiO

2catalysts Reaction conditions 119875 = 20MPa 119879 = 453K

H2DMO = 80 (molmol)

CuSiO2-SG

SiO2

Cu

CuSiO2-AE

2120579 (deg)20 40 60 80

Inte

nsity

(au

)

Figure 2 XRD patterns of the reduced CuSiO2catalysts prepared

with different methods

Table 2 The physiochemical properties of the CuSiO2 catalystsprepared by different methods

Catalyst BET surface area(m2g)

Pore volume(cm3g)

Average pore size(nm)

CuSiO2-AE 1440 051 14CuSiO2-SG 2168 031 56

the BET surface area of the CuSiO2-SG catalyst is much

larger than that of CuSiO2-AE catalyst However the average

diameter of CuSiO2-SG catalyst is much smaller than that of


(a) (b)

Figure 3 TEM images of reduced CuSiO2catalysts (a) CuSiO

2-AE and (b) CuSiO

2-SG

CuSiO2-AE catalyst and the average pore diameters are 14

and 56 nm indicating that the two catalysts havemesoporousstructures

The copper dispersion can also be observed from theTEM images Figure 3 shows the images of the reducedCuSiO

2catalysts prepared by ammonia-evaporationmethod

(Figure 3(a)) and sol-gelmethod (Figure 3(b)) respectively Itis observed that the copper species are distributed uniformlyover the CuSiO

2-SG catalyst the average particle size is

about 3-4 nm On the contrary the average Cu particle sizein the CuSiO

2-AE catalyst is about 10 nm in addition some

Cu particles obviously aggregate together implying poor Cudispersion of the catalyst The copper particles are highlydistributed on the surrounding silica supports which mightincrease the interaction between the copper species and thesupport and consequently improve the activity of the catalyst[18]

322 The Reducibility TPR measurements were carried outto investigate the reducibility of the copper species in theCuSiO

2catalysts prepared by different methods Figure 4

presents the reduction profiles of the catalysts As shown inFigure 4 there are two reduction peaks in the TPR profilesof the catalysts one occurs in the range of 495ndash515 K and theother occurs in the range of 530ndash540K which are denoted as120572 peak (the low-temperature reduction peak) and 120573 peak (thehigh-temperature reduction peak) respectively implying thepresence of different CuO species with slight differencesin ease of reducibility The 120572 peak can be assigned to thereduction of well-dispersed CuO species and 120573 peaks canbe attributed to the reduction of bulk CuO The similarassignments have also been reported for other copper basedcatalysts [19] For CuSiO

2-AE catalyst the area of 120572 peak

is much smaller than that of 120573 peak demonstrating thatthe quantity of larger CuO particles is much more thanthe smaller ones In contrast for CuSiO

2-AE catalyst the

trend changes conversely suggesting the fractions of highlydispersed CuO species is much higher than those of bulk

Inte

nsity

Temperature (K)450 500 550 600

CuSiO2-SG

CuSiO2-AE

539 K

500 K509 K

535 K

Figure 4 TPR profiles of different CuSiO2catalysts

ones The observed shift in reduction temperature maybe ascribed to the different copper particle sizes differentinteractions between copper oxide and silica and differentcopper oxide dispersions The TPR results further elucidatethat the CuSiO

2catalyst prepared by the sol-gel method can

result in a better-dispersion of copper species on the SiO2

support In addition the TPR results are consistent with TEMresults

323 The Surface Chemical States of the Catalysts The XPSspectra as well as X-ray-induced Auger spectra (XAES) ofthe reduced catalysts are illustrated in Figures 5 and 6respectively As it can be seen from Figure 5 the bindingenergy values of Cu2p

32core levels are 9324 and 9327 eV

of CuSiO2-AE and CuSiO

2-SG implying that copper has

been reduced to Cu+ andor Cu0 [20 21] Because the bindingenergy values of Cu+ and Cu0 are almost identical thedistinction between these two species present on the catalystsurface is impossible on the basis of the Cu2p level In


Table 3 Surface Cu component of the reduced catalysts based on Cu LMM deconvolution

Catalysts KE (eV)a 120572

1015840 (eV)b Cu 2p32 BE (eV) XCu+Cu0c (molmol)Cu+ Cu0 Cu+ Cu0

CuSiO2-AE 9163 9183 18487 18507 9324 179CuSiO2-SG 9165 9191 18492 18518 9327 196aKinetic energy bModified Auger parameter cCu+(Cu0) lowast 100

Cu2p

Binding energy (eV)

9327

970 960 950 940 930 920 910

Inte

nsity

(au

)

CuSiO2-SG

CuSiO2-AE

Figure 5 Cu2p photoelectron spectra of the reduced CuSiO2

catalysts

Binding energy (eV)

9165 9191

910 915 920 925

CuSiO2-SG

CuSiO2-AE

Inte

nsiti

es (a

u)

Figure 6 Cu LMMXAES spectra of the reduced CuSiO2catalysts

general Cu+ and Cu0 species can be distinguished throughtheir kinetic energies in the XAES Cu LMM line positionor the modified Auger parameters (1205721015840) [22] It is reportedthat 1205721015840 is ca 18510 eV for Cu0 and 18490 eV for Cu+ [23]As it can be seen from Figure 6 the Cu LMM spectra ofcatalysts show a broad and asymmetrical peak implying thecoexistence of Cu+ and Cu0 in the surface of the catalyst Twosymmetrical peaks centered at near 916 and 919 eV can beobtained by deconvolution of the original Cu LMM peakswhich are corresponding to Cu+ and Cu0 species [24] The

deconvolution results are summarized in Table 3 As shownin Table 3 the 1205721015840 value at ca 1849 eV is ascribed to Cu+ and1851 eV to Cu0 Comparedwith bulk Cu+ the1205721015840 values of Cu+in the catalysts are 2-3 eV lower indicating strong interactionbetween Cu+ and silica supports [25] The Cu+Cu0 arearatios derived from fitting the Cu LMM peaks are listed inTable 3 It is noted that the Cu+Cu0 area ratio on the surfaceof reduced CuSiO

2-SG is 94 more than that of reduced

CuSiO2-AEwhichmight be one reason for the enhancement

in catalytic activity for the catalyst It is reported that higheractivity can be obtained on the CuSiO

2catalyst with proper

ratio of Cu+Cu0 due to their synergetic effect The XPS andXAES results are in good agreements with TPR results It canbe concluded that the surface chemical states of the catalystsare highly effected by the preparation methods

4 Conclusions

In summary the CuSiO2catalysts for the synthesis of EG

from hydrogenation of DMOwere prepared by twomethodsone was prepared by ammonia method and the other wasprepared by sol-gel method It is found that the structurethe reducibility of CuO the particle size of Cu and thesurface chemical state are highly affected by the preparationmethod By comparison the catalyst prepared by sol-gelmethod exhibited higher activity and EG selectivity and 98DMO conversion and 96 EG selectivity can be obtainedunder the optimized hydrogenation conditions due to itssmaller Cu particles size larger BET surface area and higherdispersion in silica

Acknowledgments

The authors thank Liaoning Science and Technology Depart-ment Foundation (Grant no 2007223016) Liaoning Edu-cational Department Foundation (Grant no l2011065) andShenyang Science and Technology Department Foundation(Grant no F11-264-1-76) for financial support

References

[1] G H Xu Y C Li Z H Li and H J Wang ldquoKinetics of thehydrogenation of diethyl oxalate to ethylene glycolrdquo Industrialand Engineering Chemistry Research vol 34 no 7 pp 2371ndash2378 1995

[2] L F Chen P J Guo M H Qiao et al ldquoCuSiO2catalysts pre-

pared by the ammonia-evaporation method texture structureand catalytic performance in hydrogenation of dimethyl oxalateto ethylene glycolrdquo Journal of Catalysis vol 257 no 1 pp 172ndash180 2008


[3] G Zhenghong L Zhongchen H Fei and X Genhui ldquoCom-bined XPS and in situ DRIRS study of mechanism of Pd-Fe120572-Al

2O3catalyzed CO coupling reaction to diethyl oxalaterdquo

Journal of Molecular Catalysis A vol 235 no 1-2 pp 143ndash1492005

[4] A Yin X Guo W L Dai and K Fan ldquoThe nature of activecopper species in cu-hms catalyst for hydrogenation of dimethyloxalate to ethylene glycol Nw insights on the synergetic effectbetween Cu0 and Cu+ rdquo Journal of Physical Chemistry C vol 113no 25 pp 11003ndash11013 2009

[5] U Matteoli M Blanchi G Menchi P Prediani and F PiacentildquoHomogeneous catalytic hydrogenation of dicarboxylic acidestersrdquo Journal ofMolecular Catalysis vol 22 no 3 pp 353ndash3621984

[6] U Matteoli G Menchi M Bianchi and F Piacenti ldquoSelectivereduction of dimethyl oxalate by ruthenium carbonyl carboxy-lates in homogeneous phase Part IVrdquo Journal of MolecularCatalysis vol 64 no 3 pp 257ndash267 1991

[7] A Yin X GuoWDai andK Fan ldquoHigh activity and selectivityof AgSiO

2catalyst for hydrogenation of dimethyl oxalaterdquo

Chemical Communications vol 46 no 24 pp 4348ndash4350 2010[8] M A Karakassides A Bourlinos D Petridis L Coche-

Guerente and P Labbe ldquoSynthesis and characterization ofcopper containing mesoporous silicasrdquo Journal of MaterialsChemistry vol 10 no 2 pp 403ndash408 2000

[9] D JThomas J TWehrliM SWainwrightD L Trimm andNW Cant ldquoHydrogenolysis of diethyl oxalate over copper-basedcatalystsrdquo Applied Catalysis A vol 86 no 2 pp 101ndash114 1992

[10] L He X Chen J Ma H He and W Wang ldquoCharacterizationand catalytic performance of sol-gel derived CuSiO

2catalysts

for hydrogenolysis of diethyl oxalate to ethylene glycolrdquo Journalof Sol-Gel Science and Technology vol 55 no 3 pp 285ndash2922010

[11] A Yin C Wen X Guo W L Dai and K Fan ldquoInfluence of Nispecies on the structural evolution of CuSiO

2catalyst for the

chemoselective hydrogenation of dimethyl oxalaterdquo Journal ofCatalysis vol 280 no 1 pp 77ndash88 2011

[12] B Zhang S G Hui S H Zhang Y Ji W Li and D Y FangldquoEffect of copper loading on texture structure and catalyticperformance of CuSiO

2catalyst for hydrogenation of dimethyl

oxalate to ethylene glycolrdquo Journal of Natural Gas Chemistryvol 21 pp 563ndash570 2012

[13] Y Y Zhu S R Wang L J Zhu X L Ge X B Li and Z YLuo ldquoThe influence of copper particle dispersion in CuSiO

2

catalysts on the hydrogenation synthesis of ethylene glycolrdquoCatalysis Letters vol 135 no 3-4 pp 275ndash281 2010

[14] L Lin P B Pan Z F Zhou et al ldquoCuSiO2catalysts prepared

by the Sol-Gel method for hydrogenation of dimethyl oxalateto ethylene glycolrdquo Chinese Journal of Catalysis vol 32 pp 957ndash968 2011

[15] M Zheng T Zhao W Xu F Li and Y Wang ldquoPreparation andcharacterization of CuSiO

2catalyst by co-gelation processrdquo

Journal of Materials Science vol 42 no 19 pp 8320ndash8325 2007[16] A Yin X Guo W L Dai and K Fan ldquoEffect of initial

precipitation temperature on the structural evolution and cat-alytic behavior of CuSiO

2catalyst in the hydrogenation of

dimethyloxalaterdquo Catalysis Communications vol 12 no 6 pp412ndash416 2011

[17] C Carlini M Di Girolamo A Macinai et al ldquoSelective synthe-sis of isobutanol by means of the Guerbet reaction part 2 Reac-tion of methanolethanol and methanolethanoln-propanol

mixtures over copper basedMeOna catalytic systemsrdquo Journalof Molecular Catalysis A vol 200 no 1-2 pp 137ndash146 2003

[18] A Yin C Wen W L Dai and K Fan ldquoSurface modification ofHMS material with silica sol leading to a remarkable enhancedcatalytic performance of CuSiO

2rdquoApplied Surface Science vol

257 no 13 pp 5844ndash5849 2011[19] X M Guo D S Mao S Wang G S Wu and G Z Lu

ldquoCombustion synthesis of CuO-ZnO-ZrO2catalysts for the

hydrogenation of carbon dioxide to methanolrdquo Catalysis Com-munications vol 10 pp 1661ndash1664 2009

[20] J Toyir P Ramırez De La Piscina J L G Fierro and NHoms ldquoHighly effective conversion of CO

2to methanol over

supported and promoted copper-based catalysts influence ofsupport and promoterrdquo Applied Catalysis B vol 29 no 3 pp207ndash215 2001

[21] J Toyir P Ramırez de la Piscina J L G Fierro and N HomsldquoCatalytic performance for CO

2conversion to methanol of

gallium-promoted copper-based catalysts influence of metallicprecursorsrdquoAppliedCatalysis B vol 34 no 4 pp 255ndash266 2001

[22] F Marquez A E Palomares F Rey and A Corma ldquoCharac-terisation of the active copper species for the NOx removal onCuMgAl mixed oxides derived from hydrotalcites an in situXPSXAES studyrdquo Journal of Materials Chemistry vol 11 no 6pp 1675ndash1680 2001

[23] K Sun W Lu F Qiu S Liu and X Xu ldquoDirect synthesis ofDME over bifunctional catalyst surface properties and catalyticperformancerdquo Applied Catalysis A vol 252 no 2 pp 243ndash2492003

[24] N S McIntyre T E Rummery M G Cook and D Owen ldquoX-ray photoelectron spectroscopic study of the aqueous oxidationof monel-400rdquo Journal of the Electrochemical Society vol 123no 8 pp 1164ndash1170 1976

[25] M A Kohler H E Curry-Hyde A E Hughes B A Sextonand NW Cant ldquoThe structure of Cu SiO

2catalysts prepared by

the ion-exchange techniquerdquo Journal of Catalysis vol 108 no 2pp 323ndash333 1987

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materials


Journal ofNanomaterials


respectively In an attempt to understand the effect of Cunanoparticles dispersion andpreparationmethods on the cat-alyst structure and catalytic performance we characterizedthese catalysts by means of the techniques such as nitrogenphysisorption X-ray diffraction (XRD) X-ray photoelec-tron spectroscopy (XPS) temperature-programmed reduc-tion (TPR) and transmission electron microscopy (TEM)This work not only can provide a research foundation for thedevelopment of industrial catalysts for the synthesis of EG viaa nonpetroleum route but also can provide some deep insightfor the design of high active copper-based catalysts for otherreactions

2 Experimental Section

21 Catalyst Preparation All the reagents used are analyt-ically pure CuSiO

2catalysts were prepared by ammonia-

evaporation and sol-gelmethods with the samenominal cop-per loading of 30wt (CuO(CuO + SiO

2)) respectivelyThe

ammonia-evaporation method was carried out as followsAt room temperature 136 g Cu(NO

3)2sdot3H2O (Sinopharm

Chemical Reagent Ltd) was dissolved in 150mL of deionizedwater 42mL of 28 ammonia aqueous solution (SinopharmChemical Reagent Ltd) was added and stirred for 30minThen 420 g of silica sol (JA-25 Qingdao Haiyang ChemicalLtd) was added to the copper ammonia complex solutionand the initial pH of the suspension was 11-12The suspensionwas stirred for another 3 h Then the suspension was heatedto 363K and kept at this temperature for the evaporationof ammonia The evaporation process was not terminateduntil the pH decreased gradually to 6-7 Then the productwas filtered washed by deionized water for several times anddried at 393K for 12 h Then the product was calcined in amuffle oven at 723K for 4 h After calcination the catalyst waspelletized crushed and sieved to 20ndash40 mesh The catalystwas referred to as CuSiO

2-AE

The sol-gel method was carried out as follows Tet-raethoxysilane (TEOS Sinopharm Chemical Reagent LtdChina) and copper nitrate trihydrate were used as the silicaand copper sources respectively The mixture of ethanol(C2H5OH) and water (H

2O) was used as solvent the mass

ratio of TEOSC2H5OHH

2O was 111 The mixture was

stirred homogeneously and kept at room temperature for20 h for gelation Then the product was filtered washed bydeionized water for several times and dried at 393K for 12 hThen the product was calcined in a muffle oven at 723K for4 h After calcination the catalyst was pelletized crushedsieved to 20ndash40 mesh The catalyst is referred to as CuSiO

2-

SG

22 Catalyst Characterization XRDmeasurementswere per-formed on a Bruker D8 X-ray diffractometer with Cu-K120572radiation (120582 = 154156 A) at a scan rate of 4∘minminus1 at 45 kVand 40mA

BET surface areas were measured by N2adsorption at

77K using a Micromeritics SSA-4000 instrument Beforemeasurements samples were degassed under vacuum at298K for 3 h

The XPS measurements were performed on a Perkin-Elmer PHI 5000 ESCA photoelectron spectrometer using anAl K120572 (h120584 = 1 4866 eV) source The binding energies of theelements on the surfaces of the catalysts were corrected byusing the carbon C1s value 285 eV as an internal standard

TEM images were obtained on a JEOL JEM 2010 trans-mission electron microscope with accelerating voltage of200 kV

H2-TPR was also conducted to examine the catalyst

reducibility 50mg of the catalyst was heated in He at 673Kfor 60min followed by cooling to room temperature Thetemperature was then raised in 50mLmin of 10 H

2Ar

using a ramp rate of 10 Kmin to 823K H2consumption was

detected using TCD

23 Catalyst Testing Activity and selectivity measurementsfor DMO hydrogenation to EG were carried out in acontinuous-flow fixed-bed reactor made of stainless steel(id = 7mm) 12 g catalyst was placed into the reactor Thereaction pressure was 20MPa and the reaction temperatureis 453K Prior to the catalytic measurements the catalyst wasreduced in a streamof 10H

2N2at 553K for 4 h under atmo-

spheric pressure After cooling to the reaction temperaturethe catalyst bed was fed with 10 DMO in methanol and H

2

and H2DMO is 80 (molmol) The DMO in methanol was

supplied by a syringe pump (SSI) vaporized and mixed withthe H

2feed in an electrical heated stainless steel preheater

at 443K The hydrogen feed was controlled by the massflow controllers The exit gases were cooled down to roomtemperature in a water-cooled condenser The liquid productwas collected and analyzed by gas chromatograph (BeijingBenfenruili Ltd 3420) equipped with an FID detector

3 Results and Discussion

31 Performance of Different CuSiO2Catalysts The catalytic

properties for DMO hydrogenation to EG over the CuSiO2-

AE and CuSiO2-SG catalysts were tested For the synthesis

process of EG from hydrogenation of DMO it can beexpressed by the following reactions [17]

(COOCH3)

2+H2997888rarr CH

2OHCOOCH

3+ CH

3OH (1)

CH2OHCOOCH

3+H2997888rarr (CH

2OH)2+ CH

3OH (2)

(CH2OH)2+H2997888rarr C

2H5OH +H

2O (3)

(CH2OH)2+ C2H5OH 997888rarr HOCH

2(OH)C

2H5+H2O(4)

During reaction process first methyl glycolate (MG) isproduced by hydrogenation of DMO then further hydro-genation of MG to EG while EG can dehydrate to ethanol(ET) At certain conditions EG and ET can dehydrate to12-butanol (BDO) MG is known as a partial hydrogenationproduct while ET and BDO are called the excess hydro-genation products The EG is a major product and theother products are side products in our experiments Theconversion of DMO the selectivity of EG and the yieldof EG on CuSiO

2are shown in Table 1 Compared with













2-SG








2-SG catalyst are











2-AE


100

90

80

70

60

50

40

3004 06 08 1 12 14 16

Con

vers

ion

sele

ctiv

ity (

)

LHSV (hminus1)






H2DMO = 80 (molmol)

CuSiO2-SG

SiO2

Cu

CuSiO2-AE

2120579 (deg)20 40 60 80

Inte

nsity

(au

)





Pore volume(cm3g)


CuSiO2-AE 1440 051 14CuSiO2-SG 2168 031 56





(a) (b)


2-AE and (b) CuSiO

2-SG















2-AE catalyst the


Inte

nsity


CuSiO2-SG

CuSiO2-AE

539 K

500 K509 K

535 K
















Cu2p

Binding energy (eV)

9327

970 960 950 940 930 920 910

Inte

nsity

(au

)

CuSiO2-SG

CuSiO2-AE


catalysts

Binding energy (eV)

9165 9191

910 915 920 925

CuSiO2-SG

CuSiO2-AE

Inte

nsiti

es (a

u)









4 Conclusions



Acknowledgments


References

















2catalysts



2catalyst for the






2


















2to methanol over


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials















2-SG








2-SG catalyst are











2-AE


100

90

80

70

60

50

40

3004 06 08 1 12 14 16

Con

vers

ion

sele

ctiv

ity (

)

LHSV (hminus1)






H2DMO = 80 (molmol)

CuSiO2-SG

SiO2

Cu

CuSiO2-AE

2120579 (deg)20 40 60 80

Inte

nsity

(au

)





Pore volume(cm3g)


CuSiO2-AE 1440 051 14CuSiO2-SG 2168 031 56





(a) (b)


2-AE and (b) CuSiO

2-SG















2-AE catalyst the


Inte

nsity


CuSiO2-SG

CuSiO2-AE

539 K

500 K509 K

535 K
















Cu2p

Binding energy (eV)

9327

970 960 950 940 930 920 910

Inte

nsity

(au

)

CuSiO2-SG

CuSiO2-AE


catalysts

Binding energy (eV)

9165 9191

910 915 920 925

CuSiO2-SG

CuSiO2-AE

Inte

nsiti

es (a

u)









4 Conclusions



Acknowledgments


References

















2catalysts



2catalyst for the






2


















2to methanol over


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)


2-AE and (b) CuSiO

2-SG















2-AE catalyst the


Inte

nsity


CuSiO2-SG

CuSiO2-AE

539 K

500 K509 K

535 K
















Cu2p

Binding energy (eV)

9327

970 960 950 940 930 920 910

Inte

nsity

(au

)

CuSiO2-SG

CuSiO2-AE


catalysts

Binding energy (eV)

9165 9191

910 915 920 925

CuSiO2-SG

CuSiO2-AE

Inte

nsiti

es (a

u)









4 Conclusions



Acknowledgments


References

















2catalysts



2catalyst for the






2


















2to methanol over


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials








Cu2p

Binding energy (eV)

9327

970 960 950 940 930 920 910

Inte

nsity

(au

)

CuSiO2-SG

CuSiO2-AE


catalysts

Binding energy (eV)

9165 9191

910 915 920 925

CuSiO2-SG

CuSiO2-AE

Inte

nsiti

es (a

u)









4 Conclusions



Acknowledgments


References

















2catalysts



2catalyst for the






2


















2to methanol over


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
















2catalysts



2catalyst for the






2


















2to methanol over


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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