Conversion of syngas to higher alcohols over Cu-Fe-Zr catalysts induced by ethanol

Availableonlineatwww.sciencedirect.com°" ScienceDirectNATURAL GASCHEMISTRYELSEVIERJournal of Natural Gas Chemistry 18(2009)337-340Conversion of syngas to higher alcohols over Cu- Fe-Zrcatalysts induced by ethanolHongtao Zhang!, Xiaomei Yang, Lipeng Zhou, Yunlai Su 2*, Zhongmin Liu22. Laboratory of Natural Gas Utilization and Applied Catalysis, Dalian Institute of Chemical PhysicsChinese Academy of Sciences, Dalian 116023, Liaoning, ChinaReceived February 23, 2009: Revised April 21, 2009; Available online July 16, 2009 1AbstractEthanol induced method was applied to prepare Cu-Fe- Zr catalysts for conversion of syngas to higher alcohols. The catalytic performance of theatalysts induced by ethanol was superior to that of the catalyst prepared by the conventional precipitation method. among various procedor ethanol induced method, it was found that incorporation eth]nol in the pr titation process was the better. After incorporation of ethanol,the crystal size of Cuo decreased and the reduction of copbetter activity of Cu-Fe-Zr catalysts prepared byethanol induced procedures was probably caused by the higsKey wordsFe-Cu-Zr catalyst; CO hydrogenation; higher alcohols; ind1. Introductionpretreated by various gases for o-xylene isomerization [131which improves their catalytic performance. It was reportedThe production of liquid fuels and high-value addedthat the selectivity of methanol was significantly improvednemicals from coal has received significantly increasing inusing the catalyst prepared in the solvent of methanol [14]terest due to the limited petroleum reserves [1, 2]. Synthesis ofXu et al. has also reported that the Cu-Co-Fe catalysts obalcohols from syngas is an important pathway to realize this tained in ethanol medium or pretreated by ethanol showedprocess because syngas can be produced from relatively abun- higher activity and selectivity for synthesis of higher alcoholsdant coal resource. In recent years, various catalyst systemsfrom syngas [15, 16In the present work, we investigated in detail the prepariwere developed to synthesize alcohols from syngas, such as tion of Cu-Fe- zr based catalysts by ethanol induced metheCu-Co, Cu-Fe and MoS2 based catalysts [3-9]and their catalytic performance in the conversion of syngasHigher alcohols( C2+ OH)have potential applications as higher alcohols. The nature of the catalyst was characterizefuels, additives to increase the octane number of gasolineand materials for synthesis of fine chemicals [10]. Althorby X-ray diffraction(XRD)and temperature-programmed reduction(TPR)by Hhe conversion of syngas to higher alcohols has beenproved to some extent, the space-time yield of alcohols and/orthe selectivity of C2+ alcohols is still unsatisfactory. There-ore, it is highly desirable to seek catalysts with high actinity and selectivity for synthesis of higher alcohols from syn- 2.1. Catalyst preparationas. The pretreatment of solid catalysts can change theirhe oxidative esterification of ethanol [12], and HY zeolite for preparation of Cu-Fe-Zr catalys e usedC12-8H20 andstructure, such as Au/Al2O3 pretreated by H2 for oxida-Cu(NO3)2. 3H2O, Fe(NO3).9H2O, ZrOtion of Co [ll, Sb-Mo-O catalyst pretreated by ethanol for K2 CO3 were of A R grade and was the materialsCorrespondingauthor.Tel:0371-67766076:Fax:0371-67766076:E-mail:yunlaisu@zzu.edu.cnFoundation items: Natural Science Foundation of State Key Laboratory of Coal Conversion(No09H中国煤化工CNMHGCopyright@2009, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. All rights reservedoi:10.1016/S1003-9953(08601127338Hongtao Zhang et al Journal of Natural Gas Chemistry VoL. 18 No. 3 20092.1.1. Cu-Fe-Zr catalyst prepared by conventional method3. Results and discussionCu-Fe-Zr sample prepared by conventional method was 3.1. Crystal phase analysis of Cu-Fe-Zr based catalystsnamed as sl. First, Cu(NO3)2 3H20, Fe(NO3 )3 9H2O andZrOCl. 8H,O were dissolved in water to form a solution TheFigure I shows the XRD patterns of Cu-Fe-Zr based cat-molar ratio of Cu: Fe: Zr was 2: 1: 0.04. Then this solu- alysts before reduction. The phase of Cuo (JCPDS card Notion and the aqueous solution of K2 CO3 were simultaneously 48-1548) was detected in SI and S2 samples, but no ZrO2 andadded drop-wise into a beaker containing water. The mix- ferric oxide was detected. The result suggested that the exper-ture was stirred at 343 K and its pH value was kept at 7.5. imental methods had no significant effect on the phase formaThe precipitate was aged at 343 K for I h, then it was filtered tion of the Cu-Fe- Zr catalysts. But the peak intensity of Cuoand washed thoroughly with distilled water. After drying at in S2 was lower than that in S1. It indicated that the addition693K for 12 h, the sample was calcined at 623K in air of ethanol probably decreased the crystal size of Cuofor 5 h2. 2. Cu-Fe-Zr catalyst prepared by different ethanol induced methodsFour catalysts(S2-S5) were prepared by ethanol inducedmethod. Among them, catalyst S2 was prepared by addin入ethanol into water in a beaker, catalyst S3 was prepared bywashing the precipitate with ethanol-water solution, catalysts4 was prepared by drying in the presence of ethanol vapor,and catalyst S5 was prepared by calcination in the ethanol va-por. All the other experimental conditions for S2-S5 were theM%小wsame with catalyst sI2. 2. Catalyst characterizationFigure 1. XRD patterns of the as-synthesized SI and $2D patterns were recorded on a Philips Pdiffractometer fitted with Cu Ko radiation(=1.5404 A). 3.2. H2-TPR measurementsH2-TPR experiments were carried out with a homemade ap-paratus. All samples(20 mg)were first pretreated at 373 K inThe H2-TPR results of the Cu-Fe-Zr catalysts are pre-Ar(50 ml/min) for I h. For TPR measurements, the samples sented in Figure 2. Every sample exhibited two reductionwere heated from 373 K to 973 K at a rate of 10 K/min in an peaks in the range of 500-700 K and 700-900 K. The first8 vol% H2/Ar flow (50 ml/min)peak was attributed to the reduction of copper species, and thesecond peak was related to the reduction of ferric species. The2.3. Catalytic testsfirst reduction peak of Sl, S2, S3, S4 and $5 samples centeredat 630, 583, 610, 614 and 609K, respectively. The reductionak of copper species in S2-S5 samples shifted to lowerThe catalytic performance was evaluated in a fixed-bedstainless-steel micro-reactor with 6 mm inner diameter. Priorto reaction, the catalysts were reduced in-situ by the reactant gas(n(H2)/n(Co)=2.0)at atmospheric pressure, whichcontained 8.0 mol%COz and 0.4 mol%CHa. The followingtemperature-programmed procedure was employed(1)room temperature -523 K for I h and keeping thetemperature at 523 K for 0.5 h2)523 K-573 K for I h and keeping at 573 K for 0.5 h(3)573K-623 K for I h and keeping at 623 K for 2 hAfter pretreatment, the temperature was decreased slowly to593 K and the catalytic reaction was performed under the conditions of 6.0 MPa and GHSV of 20000 h. The steady-staterV凵中国煤化工activity was measured using an on-line gas chromatograph373CNMHG373with a 4 mmx224073n stainless-steel B73 column and an 673Q36/fId detectorFigure 2. Hcurves of the as-synthesized S1-S5TenDer at ure( kJournal of Natural Gas Chemistry VoL. 18 No. 3 2009temperature compared with that of Sl, indicating that the re- by ethanol induced method were higher than those of catalystluction of copper species became easier because of its smaller prepared by the conventional co-precipitation method. Adcrystal size. Additionally, the reduction of copper specieditionally, the ethanol-incorporated method also affected theS2 sample was the easiestactivity and selectivity of the catalysts. Among all the cata-lysts, the S2 and s3 samples exhibited higher time-space yield3.3. Effect of ethanol-incorporated method on the catalytic of alcohol(ROH) and selectivity of C2+ OH than other cataperformance of Cu-Fe-Zr catalystslysts. Over S2 catalyst, the time-space yield and selectivity ofROH were 1. 25 gml.h and 57.9 wt%, respectively. TheThe catalytic performance of Cu-Fe- Zr catalysts prepared percentage of C2+ OH in products of alcohols was 69.7by the conventional co-precipitation and ethanol induced co- which was higher than that over Cu-Fe-Co catalyst inducedprecipitation method in the conversion of syngas to alcohols is by ethanol [16], Cu-Co [5], or Cu-Co-Zn-zr [17] catalyst deshown in Table 1. The main products were alcohol, dimethyl scribed in literature. The better catalytic performance probather methane and ethene. It was obvious that the activity bly benefited from the small crystal size of copper species inand selectivity of alcohol over Cu-Fe- Zr catalysts prepared S2 catalyst [I7]Table 1. Results of Co hydrogenation over Cu-Fe-Zr based catalysts prepared by the conventionalo-precipitation and ethanol induced co-precipitation methodConversionCatalystSelectivity(wt%)Yield of rohDistribution of alcohols(wt%)ROH(g-mI-l-h-) of Co(wt%) MeOH EtOH PrOHBuoh C2+OH12.869.723.055.030.469929.211.1Reaction conditions: T=593 K, P=6.0 MPa, GHSV=20000 h, n(H2)/n(CO)=2.3: ROH represents alcohol3.4. Catalytic performance of Cu-Fe-Zr catalysts prepared by tor K2 CO3 solution, the highest space-time yield of ROHthe incorporation of ethanol in the course of precipitationreached 1.76g ml -h with 73.7 wt%C2+OH selectivitywhen 20 ml ethanol was added as shown in table 3. when weAs discussed above, the catalyst prepared by the incorpo- added ethanol (8 mI)into the precipitation medium, the selecration of ethanol in the course of precipitation showed better tivity of C2+ OH was 71.6 wt% at the highest space-time yieldcatalytic performance, so we further investigated this prepara- of ROH (1. 45 g. ml.h )as shown in Table 4. When maktion method. The addition of ethanol into metal nitrate solu- ing comparisons with all the preparation methods, this methodtion, precipitator K2 CO3 solution and precipitation medium, was superior to the formers. It consumed the least amountand the adding amount of ethanol were investigated. Theof ethanol to obtain the higher space-time yield of roh andsults of Co hydrogenation to alcohols over these catalysts are selectivity for C2+OH. In order to study why the amount oflisted in Table 2, Table 3 and Table 4, respectively. Over ethanol influenced the catalytic performance, we performedall the catalysts, the main products of alcohol are MeOH, the H2-TPR of the catalysts prepared by adding ethanol intEtOH, PrOH and BuOH. But the space-time yield of roh the precipitation medium(Figure 3). It was found that theand the selectivity of C2+OH are influenced by the amount of reduction temperature of Cu species decreased with increasethanol added during the catalyst preparation. Over the cat- ing the amount of ethanol from 0 to 24 ml. But when thealysts prepared by adding ethanol into metal nitrate solution, amount of ethanol was further increased, the reduction tem-the optimum amount of ethanol was 10 ml, where the high- perature increased. So it can be speculated that the amount ofest space-time yield of ROH (1.36 g.ml -I-h-)with C2+OH ethanol affected the state of the active copper species,whichselectivity for 74.2 wt% was obtained as shown in Table 2. in turn influenced the catalytic performance of the Cu-Fe-ZrFor the catalysts prepared by adding ethanol into precipita- catalystsTable 2. Results of Co hydrogenation over Cu-Fe-Zr based catalysts prepared by adding different amountof ethanol into metal nitrate solutionAdding amount of ethanolSpace-time yield of ROHDistribution of alcohols(wt%)Meoh1.3631.274.271.126.9Reaction conditions: T=593 K, P=6.0MPa, GHSV=20000h-I n(H2)/n(CO)=2.3: ROHH中国煤化工731CNMHG340Hongtao Zhang et al Journal of Natural Gas Chemistry VoL. 18 No. 3 2009Table 3. Results of Co hydrogenation over Cu-Fe-Zr based catalysts prepared by adding different amountof ethanol into precipitator K2 CO3 solutionield of rohag-ml-.h-l)1.04B一26.334.756Reaction conditions: T=593K, P=6.OMPa, GHSV=20000h, n(H2)n(CO)=2,3: ROH represents alcoholTable 4. Results of CO hydrogenation over Cu-Fe-Zr based catalysts prepared by adding different amount of ethanol into precipitation mediumAdding amount of ethanolpace-time yield of rohDistribution of alcohols(wt%)(ml)(gml.h)MeohEtOHPrOHC,OH39927.323.060287381.0832.8Reaction conditions: T=593 K, P=6.0MPa, GHSV= 20000h, n(H2)n(CO)=2.3: ROH represents alcoholReferences入80 ml EtOH[1 Khodakov A Y, Chu W, Fongarland P. Chem Rev, 2007, 1040 ml EtoH[2] Lohitharn N, Goodwin Jr. J G. 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