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Catalysis Today 232(2014)53–62

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Catalysis

Today

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c a t t o

Dehydrogenation of alkane to light ole?n over PtSn/?-Al 2O 3catalyst:Effects of Sn loading

Mi-Hyun Lee a ,b ,Bhari Mallanna Nagaraja a ,Kwan Young Lee b ,Kwang-Deog Jung a ,?

a Clean Energy Research Centre,Korea Institute of Science and Technology,P.O.Box 131,Cheongryang,Seoul 136-791,Republic of Korea b

Department of Chemical &Biological Engineering,Korea University,Anam-dong,Seongbuk-gu,Seoul 136-701,Republic of Korea

a r t i c l e

i n f o

Article history:

Received 12July 2013Received in revised form 24September 2013

Accepted 2October 2013

Available online 29October 2013

Keywords:Light ole?n

Dehydrogenation of linear alkane PtSn alloy Effects of Sn

a b s t r a c t

Pt 0.5Sn x .x /?-Al 2O 3catalysts with different amount of tin (0.5,0.75,1.0and 1.5wt%)were prepared by a co-impregnation method.Propane dehydrogenation was performed at 873K and a GHSV of 53,000mL/(g cat h).The Pt 0.5/?-Al 2O 3catalyst showed severe deactivation in alkane dehydrogenation reaction.The Sn addition decreased the cracking products of C 1–C 2and the Pt 0.5Sn 0.75catalyst with the highest Pt dispersion showed the highest C 3yield and C 3selectivity.n-Butane dehydrogenation was performed at 823K and a GHSV of 18,000mL/(g cat h).Similarly to propane dehydrogenation,the Sn addition to the Pt 0.5/?-Al 2O 3catalyst decreased the cracking products of C 1–C 3.However,the Pt 0.5Sn 1.0showed the highest n-C 4yield and the catalyst was steadily deactivated even at 823K differently from propane dehydrogenation at 873K.

The small amount of Sn addition improved the C 3and n-C 4selectivity by blocking the cracking sites of Pt catalyst.The PtSn alloy formed after the reduction at 500?C.The PtSn formation can enhance the C 3and n-C 4selectivity.The Pt dispersion on the Pt 0.5/?-Al 2O 3catalyst increased with the Sn addition up to 0.75wt%.The highest Pt metal dispersion was observed on the Pt 0.5Sn 0.75catalyst.The conclusion was given to the Sn effects on the increase of Pt dispersion to enhance the activity as well as on the electronic and geometric effect of PtSn alloy to increase the stability and ole?n selectivity.

1.Introduction

The catalytic dehydrogenation of light alkanes such as propane and butane is of great interest due to the growing demand of light ole?ns.The catalytic dehydrogenation propane has received much attention as an alternative way for the production of propylene because of an uncertainty of oil price and the growing demand of light ole?n in the past ten years.Recently,there is an increased demand for the production of propylene [1,2].Propylene was used in re?nery for alkylation and oligomerization reactions to produce high-octane clean fuel.The catalytic dehydrogenation of butanes became more attractive for the production of C 4ole?ns.The increased demand for C 4ole?ns has caused the prices to soar.The C 4ole?ns were used for the industrial application such as plastics,synthetic rubbers,automotive fuel components,and petro-chemical products [3–5].In particular,n-butenes can be considered as a feedstock for the production of 1,4-butadiene.Monometallic Pt catalysts are active for alkane dehydrogenation reaction,but they are severely deactivated with time on stream,and their selectiv-ity toward propylene and n-butenes are very low.The main cause

?Corresponding author.Tel.:+8229585218;fax:+8229585219.

E-mail addresses:jkdcat@kist.re.kr ,jkdyym@https://www.wendangku.net/doc/e718098043.html, (K.-D.Jung).

of the deactivation of the monometallic Pt catalysts is coke forma-tion.The low selectivity results from cracking and isomerization reactions [3,6–13].The addition of Sn to Pt supported catalyst has been widely studied in the dehydrogenation of light alkanes to light ole?ns.The roles of Sn were proposed to modify the electronic and geometric properties of Pt.The sizes of platinum ensem-bles were decreased by the geometric effect of Sn,which reduced hydrogenolysis and coking reactions [14–16].Sn could also modify the electronic density of Pt,either by the positive charge transfer from Sn n +species or by the different electronic structures of PtSn alloys.The modi?cation of electronic nature or geometric environ-ment of the platinum atoms induced a decrease in the adsorption energy of precursors for coke formation [17–23].

Many authors reported the PtSn catalytic systems with differ-ent supports [24–28],zeolites [29,30],mesoporous materials [31],alkali metals (Na,K)and rare earth metal (La,Ce,Y)[9,32–36,7]for propane dehydrogenation reaction.Tahriri et al.studied the in?uence of solvent in the preparation of PtSn/?-Al 2O 3catalyst for propane dehydrogenation reaction.The PtSn/?-Al 2O 3cata-lyst prepared with ethanol showed the better activity among the other solvents such as water and acetone [37].Many authors reported on the PtSn catalysts with various supports [4,5,12,13,16,19–21,32,38–41]and alkali promoted (Mg,Li,K and Na)[14,21,42,43]PtSn catalysts for isobutane dehydrogenation

54M.-H.Lee et al./Catalysis Today232(2014)53–62

reaction.The catalytic activity depended mainly on the com-position of Sn and Pt,which exhibit low electronic interaction in probable alloys formation[44,45].Recently,we reported the selective and stable bimetallic Pt1.5Sn x.x/?-Al2O3catalyst for dehy-drogenation of n-butane to n-butenes[46].It was suggested that the PtSn alloy increased the n-C4selectivity by blocking the crack-ing and hydrogenolysis sites of the Pt catalyst.It was con?rmed by HAADF STEM-EDS,HRTEM and XRD studies that most of Pt and Sn components on the PtSn catalysts were in PtSn alloy after the reduction at500?C.

Based on this information,we studied on propane and butane dehydrogenation over the Pt0.5Sn x.x catalyst with low Pt content, which are important for the practical application in this study.The Pt,Sn and PtSn catalysts with different Sn contents on?-Al2O3 were studied for selective dehydrogenation of alkane(propane to propylene and n-butane to butene)under industrially rele-vant conditions.The catalytic behaviors of Pt0.5Sn x.x/?-Al2O3were compared for the dehydrogenation of propane and n-butane.XRD patterns and TPR pro?les con?rmed the presence of PtSn alloy on the prepared bimetallic PtSn catalysts.TPR analysis indicated that the reduction behaviors of Pt and Sn oxides differed considerably, depending on the Sn contents.The propane dehydrogenation was conducted at873–923K and n-butane reaction was conducted at 773–873K,and the characters of the catalysts in CO chemisorption, XRD and TPR analysis explained the activity of the catalysts.

2.Experimental

2.1.Preparation of the catalyst

The0.5weight percentage of Pt with the different amount of Sn(0.5,0.75,1.0and1.5wt%)on?-Al2O3catalyst was prepared by a co-impregnation method,using hydrogen hexachloroplatinate (IV)hydrate(Kojima Chemical Co.,Ltd.,South Korea,purity=99%) and tin chloride(Sigma–Aldrich,St.Louis,USA,purity=98%)salt as precursors.The weighed amount of PtSn salt was placed in a50mL beaker and dissolved in a required quantity of ethanol. The sphere-shaped?-Al2O3support(～3mm)was prepared by cal-cining the spherical?-Al2O3at1273K for6h.The?-Al2O3support was added into the beaker with Pt and Sn solution.Ethanol was removed by evaporation on a hot plate,and the residue was dried at393K overnight and calcined at773K for4h in air.The prepared 0.5wt%Pt–x.x wt%Sn/?-Al2O3catalysts with different Sn contents was designated as(PtSn)0.5,Pt0.5Sn0.75,Pt0.5Sn1.0,and Pt0.5Sn1.5, and monometallic catalysts was designated as Sn0.75and Pt0.5. 2.2.Characterizations of catalysts

The XRD patterns of the prepared catalysts were recorded on a diffractometer(M/S,Shimadzu Instruments,Japan)with Ni-?ltered Cu K?( =1.5418?A)as a radiation source.The oper-ating voltage and current were40kV and30mA,respectively.

A scanning rate of2?was2?min?1.The BET surface areas and N2adsorption–desorption measurements were performed at77K using an automated gas sorption system(Belsorp II mini,BEL Japan, Inc.,).The Barrett–Joyner–Halanda(BJH)method was used for the pore size distribution.The TPR experiments were carried out using a temperature program analyzer(BELCAT,BEL Japan,Inc.).For TPR studies,0.1g of a calcined sample was placed between quartz wool in a U-type quartz reactor.The sample was thermally treated under an Ar stream at673K for2h to remove physically adsorbed water and other impurities.The catalysts were cooled down to the room temperature under Ar gas.After the pre-treatment,the cat-alysts were heated at10K min?1from room temperature up to 1073K in5%H2/Ar stream with a?ow rate of30mL min?1.The CO chemisorptions were performed with a pulse chemisorption mode (BELCAT,BEL Japan,Inc.).Prior to measurements,0.050g of a sam-ple was thermally treated under a He stream at773K for50min to remove physically adsorbed water and other impurities.The sam-ple was cooled down to room temperature and heated to823K with a heating rate of10K min?1using pure H2at a?ow rate of 50mL min?1.The sample was then reduced in a pure H2?ow at 823K for2h.After the reduction at823K,the sample was purged with a He gas at the same temperature for1h.After cooling to323K, the10%CO/He gas was introduced for the CO chemisorption.CO loop gas was used for each pulse,and the pulse injections were repeated until saturation.The amount of CO was measured using a thermal conductivity detector.The metal dispersion of each cat-alyst was then calculated from the amount of CO adsorbed,taking the stoichiometry factor(SF)as one for CO/Pt atm.

High-resolution TEM images of the Pt and Sn particles were characterized by using FEI(Technai F20G2,The Netherlands) microscopy(Accelerating voltage:50–200kV,Image resolu-tion:<0.23nm,Electro probe size:<0.3nm,Magni?cation: 25–1,030,000×,Specimen double tilting:±40?/±20?).The reduced catalyst samples were dispersed in ethanol solution using ultra-sonic bath for30min.The resulting solution was deposited on copper grid coated with a carbon?lm,and alcohol was evaporated. Finally,the sample on the copper grid was used for the HRTEM anal-ysis.The metal Pt and Sn compositions on the prepared catalysts were determined by Atomic Absorption Spectroscopy(AAS)and Inductively Coupled Plasma-Atomic Emission Spectrometer(ICP-AES).

2.3.Activity measurement

The prepared catalysts were?rst crushed and sieved using test-ing sieve(wire material,S/STEEL,CHUNG GYE SANG GONG SA). The?nal particle size was in the ranges of180–435?m before the activity test.The propane dehydrogenation was carried out at873K at an atmospheric pressure using0.080g of the catalyst after the H2reduction.The internal diameter of?xed bed tubular quartz reactor was10mm,and the catalyst bed length between the quartz wool layers in the reactor was approximately3–4mm. Before each experiment,the sample was reduced in a pure hydro-gen(99.99%)?ow(30mL min?1).The reduction temperature was increased slowly from room temperature to883K(10K min?1)and maintained at883K for2h.After the reduction,C3H8:H2feed gases with a molar ratio of3:2were introduced into the catalytic reac-tor for the reaction,and the total gas?ow rate was kept constant at30mL min?1.The n-butane dehydrogenation reaction was car-ried out at823K at atmospheric pressure using0.1g of the catalyst after the H2reduction.The reactor length and diameter was almost similar to the propane reactor.The sample was reduced in a pure hydrogen(99.99%)?ow(30mL min?1).The temperature during the reduction was increased slowly from room temperature to823K (10K min?1)and maintained at823K for2h.After the reduction, H2:N2:n-C4H10feed gases with a molar ratio of1.0:1.0:1.0were introduced into the catalytic reactor for the reaction,and the total gas?ow rate was kept constant at30mL min?1.The products and reactants were analyzed with an on-line GC(FID detector,Series M 600D,Younglin Co.)equipped with a capillary column(GS-Alumina, Agilent Technologies,USA,i.d.:0.53mm,length:50m).

3.Results and discussion

3.1.Catalyst characterization

3.1.1.Physical properties of the catalysts

Fig.1shows the XRD patterns of the calcined bimetallic cata-lyst samples containing different amounts of Sn.All the calcined

M.-H.Lee et al./Catalysis Today 232(2014)53–62

Fig.1.X-ray diffractograms of the calcined Pt 0.5Sn x .x /?-Al 2O 3catalysts with dif-ferent Sn contents:(a)?-Al 2O 3,(b)Sn 0.75,(c)Pt 0.5,(d)(PtSn)0.5,(e)Pt 0.5Sn 0.75,(f)Pt 0.5Sn 1.0,and (g)Pt 0.5Sn 1.5.

catalysts showed ?-Al 2O 3phases only (ICDD ?le no.:47-1771).The reduced catalysts (Fig.2)showed PtSn alloy phases (ICDD ?le no.:25-0614)as well as ?-Al 2O 3.The XRD patterns of the reduced (PtSn)0.5and Pt 0.5Sn 1.5samples showed the PtSn alloy phase clearly,while those of the reduced Pt 0.5Sn 0.75and Pt 0.5Sn 1.0samples did not.The absence of PtSn alloy phase of the reduced Pt 0.5Sn 0.75and Pt 0.5Sn 1.0samples can be due to the small PtSn alloy particles.The HRTEM and CO chemisorption studies in Table 3showed that the metal particle sizes were in the order of (PtSn)0.5>Pt 0.5Sn 1.5>Pt 0.5Sn 0.75～=Pt 0.5Sn 1.0.The PtSn phases in XRD patterns are closely related to the particle size measurements by the HRTEM and CO chemisorption.It was con?rmed that most of Pt components were in PtSn alloy phases on the catalysts with Pt and Sn components after the reduction at 500?C,which was resulted from the high Sn mobility in the reduction condition [46].Table 1shows the BET surface area and pore size distribu-tion of the calcined and reduced Pt 0.5Sn x .x /?-Al 2O 3catalysts with different Sn contents.The loading amounts of the prepared cat-alysts were analyzed using AAS/ICP analysis.The BET surface area,pore volume,and average pore diameter of ?-Al 2O 3were 98m 2g ?1,0.360cm 3g ?1,and 15nm,respectively.The BET sur-face area of the calcined monometallic Pt 0.5catalyst was similar to that of the reduced one,while that of the calcined Sn

0.75

Fig.2.X-ray diffractograms of the reduced Pt 0.5Sn x .x /?-Al 2O 3catalysts with differ-ent Sn contents:(a)Sn 0.75,(b)Pt 0.5,(c)(PtSn)0.5,(d)Pt 0.5Sn 0.75,(e)Pt 0.5Sn 1.0,and (f)Pt 0.5Sn 1.5

Fig.3.TPR pro?les of the calcined Pt 0.5Sn x .x /?-Al 2O 3catalysts with different Sn contents:(a)Sn 0.75,(b)Pt 0.5,(c)(PtSn)0.5,(d)Pt 0.5Sn 0.75,(e)Pt 0.5Sn 1.0and (f)Pt 0.5Sn 1.5.

sample decreased drastically after the reduction (from 94to 88m 2g ?1).The decrease of the BET surface areas of the calcined Sn 0.75sample after the reduction can be indicative of the strong interaction between Sn and alumina.In that point of view,the BET surface area of the calcined bimetallic catalysts decreased with an increase in Sn amount after the reduction.However,the pore volume (0.359–0.355cm 3g ?1)and the average pore diam-eter (14–15nm)of the calcined sample varied slightly after the reduction.

3.1.2.Temperature programmed reduction (TPR)studies

Fig.3shows the TPR pro?les and the hydrogen consumption of the monometallic Pt 0.5,Sn 0.75and bimetallic Pt 1.5Sn x .x catalysts with different Sn content on ?-Al 2O 3.Table 2shows the reduc-tion temperature,hydrogen consumption,and percentage of the reduction of mono-and bimetallic catalysts.All the TPR pro?les were de-convoluted using Lorentzian–Gaussian functions.In the TPR pro?les of the monometallic Pt 0.5catalyst (Fig.3a),the low-temperature reduction peak at 529K with a small shoulder at 421K was assigned as the reduction of the Pt species in the weak inter-action with the support.The other peak at 649K was assigned to the reduction of the Pt species in the strong interaction with the support [47].The reduction peaks at 777and 821K can be

56M.-H.Lee et al./Catalysis Today232(2014)53–62

Table1

BET surface area and pore size distribution of mono and bimetallic Pt0.5Sn x.x/?-Al2O3catalysts with different tin contents.

Catalysts(wt%)From ICP(wt%)BET surface area(m2g?1)Pore volume of

calcined catalysts

(cm3g?1)Average pore diameter of calcined catalysts (nm)

Pt Sn Calcined Reduced

(PtSn)0.50.450.597920.35715 Pt0.5Sn0.750.50.7698910.35915 Pt0.5Sn1.00.420.9198890.35715 Pt0.5Sn1.50.42 1.4497860.35515 Pt0.50.43–98970.35815 Sn0.75–0.7294880.35115?-Al2O3––98–0.36015

Table2

H2-TPR pro?les of mono and bimetallic Pt0.5Sn x.x/?-Al2O3catalysts with different Sn contents.

Catalysts

(wt%)

?peak?peak?peak?peak

Temp./K (Area%)H2consumption

(mmol H2g cat?1)

Temp./K

(Area%)

H2consumption

(mmol H2g cat?1)

Temp./K

(Area%)

H2consumption

(mmol H2g cat?1)

Temp./K

(Area%)

H2consumption

(mmol H2g cat?1)

(PtSn)0.5––590(18),

661(9)0.0193,0.0096771(60),

878(3)

0.0643,0.0032955(10)0.0107

Pt0.5Sn0.75478(1),

522(54)

0.0014,0.0736650(21)0.0286766(21)0.0286960(3)0.0041

Pt0.5Sn1.0468(13),

550(40)

0.0215,0.0661648(6)0.0099714(36)0.0595948(5)0.0082

Pt0.5Sn1.5537(60)0.1339648(3)0.0067709(33)0.0737936(4)0.0089 Pt0.5421(3),529

(2)

0.0015,0.0010639(22)0.0108777(64)0.0315821(9)0.0044

Sn0.75––619(8),

624(13),0.0069,0.0113687(21),

740(7),

769(26)

0.0182,0.0061

0.0226,

887(25)0.0217

attributed to oxychlorinated Pt species,which originated after the impregnation of the support with chloroplatinic acid and the prepa-ration method(drying and calcinations step)[48,49].If the calcined Pt0.5catalyst consists of PtO2and PtO phases,the hydrogen con-sumption should be0.034and0.068mmol(g cat?1),respectively. The hydrogen consumption of Pt1.5is0.049mmol(g cat?1)in the TPR experiment.Therefore,the calcined Pt0.5catalyst can be a mixed phase of PtO2and PtO.In the case of Sn1.5catalyst(Fig.3b), a small reduction peak for a?nely dispersed Sn species at619and 624K appeared.The broad reduction peaks at687,740and769K could be due to the reduction of Sn4+/Sn2+and/or Sn2+/Sn0species, respectively[12,50].The broad peak at887K can be assigned to the reduction of Sn2+to Sn0in a high interaction with the support [51].If the calcined Sn0.75is in the SnO or SnO2phases,the hydro-gen consumption of the calcined Sn0.75sample would be0.063or 0.126mmol(g cat?1),respectively.The hydrogen consumption of the Sn1.5is0.087mmol(g cat?1).Therefore,the calcined Sn0.75cat-alyst can be a mixed phase of SnO and SnO2.The TPR pro?les of the Pt0.5and Sn0.75sample are overlapped in the temperature range up to900K,indicating that the Pt and Sn species can be co-reduced in this range.

The TPR pattern of bimetallic(PtSn)0.5catalyst(Fig.3c)showed peaks at590,661,771,878,and955K.The reduction peaks of the (PtSn)0.5catalyst were not so much different from those of the Pt0.5catalyst,indicating that the presence of Sn oxides affected on the reduction of Pt species a little.The peaks at590and661K (?peaks)can be assigned to the co-reduction of the Pt species with Sn species[44,52],because Sn oxides can also be reduced in the temperature ranges.The reduction peak at771and878K (?peaks)can be assigned mainly to the reduction of Sn4+/Sn2+ and/or Sn2+/Sn0species.The reduction peak at955K(?peak)can be attributed to the reduction of Sn2+to Sn0,as described previously regarding the reduction of the Sn0.75sample.The average parti-cle size of the reduced the(PtSn)0.5catalyst is the largest among the bimetallic catalysts as shown in Table3.That indicates that the characters of the(PtSn)0.5can be close to those of the Pt0.5. The reduction peaks of the Pt0.5Sn0.75(Fig.3d)appeared at478, 522,650,766and960K.The reduction peak at478and522K (?)can be assigned to the reduction of the Pt species and the co-reduction of Pt and Sn,which is related to the Pt species in the weak interaction with the support.The weak interaction of Pt with the support on the bimetallic catalysts with high Sn content can be

Table3

The metal dispersion,metal surface area and average particle size of Pt0.5Sn x.x/?-Al2O3catalysts with different Sn contents was analyzed by CO chemisorption.

Catalysts(wt%)Amount of CO adsorbed

(cm3STP g cat?1)

Metal dispersion(%)Speci?c metal surface area(m2g cat?1)Average particle size(nm)

CO a HRTEM b (PtSn)0.50.05711.10.12310.29.3

Pt0.5Sn0.750.10518.30.226 6.2 6.2

Pt0.5Sn1.00.08317.20.179 6.5 5.9

Pt0.5Sn1.50.04910.20.10611.07.2

Pt0.50.024 5.00.05322.512.6

a Calculated from CO chemisorption.

b Mean particle size of the metal catalyst from HRTEM images using at least20visible particles.

M.-H.Lee et al./Catalysis Today232(2014)53–6257

due to the strong interaction of Sn and support as described in the effect of Sn on the decrease of the BET surface area after the reduc-tion.The peak at650K(?)can be assigned to the co-reduction of the Pt species with Sn species as described in the(PtSn)0.5.The peaks at766and960K can be assigned to the?peak and the?peak,respectively.The reduction peaks of the Pt0.5Sn1.0(Fig.3e) appeared at468,550,648,714,and948K.The peaks at468and 550K can also be assigned to the?peaks,and the peaks at648, 714and948K can be assigned to the?,?and?peak,respectively. The reduction peaks of the Pt0.5Sn1.5catalyst(Fig.3f)appeared at537,648,709,and936K.The peak at537can be determined as the?peak,the peaks at648,709,and936K can be assigned as the?,?and?peak,respectively.The hydrogen consumption of the?peak of the Pt0.5Sn0.75,Pt0.5Sn1.0and Pt0.5Sn1.5catalyst increased with an increase in Sn amount.Yu et al.reported that the low-temperature reduction peak in bimetallic PtSn/?-Al2O3cat-alysts was slightly shifted toward higher temperature than that of Pt/?-Al2O3,which can lead to the formation of PtSn alloy[53]. In our case,the hydrogen consumption at low reduction tempera-ture increased with an addition of Sn,which indicates that part of Sn oxides was also reduced in the presence of Pt at low temper-ature.A lot of hydrogen consumption at low temperature means that both Pt and Sn oxides were reduced.Therefore,PtSn alloy could also form at low reduction temperature.The PtSn alloy at low reduction temperature can retard the Pt migration or Pt sin-tering,resulting in the high Pt dispersion on the PtSn bimetallic catalysts.

3.1.3.CO chemisorption

Table3shows the metal surface areas(MSA),metal disper-sions(D),and particle sizes(PS)of the Pt metal particles for the samples prepared by CO chemisorption.The monometallic Pt0.5catalyst had a very low dispersion and MSA,and greater particle size(>22nm).Both CO chemisorption and HRTEM analy-sis of bimetallic Pt1.5Sn x.x catalysts with different amounts of Sn showed that the metal particle size decreased with an increase in Sn content up to0.75wt%.For the Pt0.5Sn1.5catalyst with a higher Sn load,the metal dispersion(10.2%)and metal surface area(0.106mmol(g cat?1))rather decreased,resulting in the par-ticle size of about11nm.Va′?zquez-Zaval et al.showed the Pt core and Sn shell structure of Pt0.2Sn0.8on SiO2support[28],indi-cating that Pt particles can be encapsulated with Sn in a PtSn bimetallic catalyst with high Sn content.Then,the PtSn particle size increased.The Sn particles encapsulated the Pt particles,when Sn was added to the Pt catalyst with a Sn/Pt weight ratio higher than3.0.Similarly to the results of PtSn/SiO2samples,the crit-ical weight ratio of Pt/Sn for encapsulation was estimated to be 3.0for the Pt0.5Sn1.5sample.In that point,the low metal sur-face area of the Pt0.5Sn1.5catalyst can be due to the encapsulation of Pt by Sn.The Pt particle size of the Pt0.5Sn0.75catalyst was the smallest among the prepared catalysts,while that of the Pt0.5 catalyst was the largest.The experimental results indicate that Pt metal sintering during the reduction can be prevented in the presence of Sn.XRD showed the PtSn alloy formation and TPR showed that the reduction temperature of metal oxides decreased so much in the presence of Sn.The co-reduction of Pt and Sn could result in PtSn alloy formation.Therefore,it can be sug-gested that PtSn alloy formation at low temperature retarded the Pt sintering during the reduction step.The sintering retardation by PtSn alloy resulted in high Pt dispersion on the bimetallic PtSn catalysts.The further Sn addition(Pt0.5Sn1.5)rather enhanced the sintering,resulting in the smallest Pt particle size on the Pt0.5Sn0.75catalyst.It is plausible that the Pt metal particle migra-tion can be retarded by the PtSn alloy formation during the reduction.3.1.4.High resolution transmission electron microscopy(HRTEM) studies

Fig.4shows HRTEM images and particle size distribution of the reduced Pt0.5Sn x.x catalysts.The HRTEM images show that the Pt particle sizes of the reduced Pt0.5,(PtSn)0.5,Pt0.5Sn0.75,Pt0.5Sn1.0 and Pt0.5Sn1.5catalysts were about12.6,9.3,6.2,5.9and7.2nm, respectively.It was con?rmed by the HRTEM analysis that the par-ticles size of the Pt0.5Sn0.75catalyst was the smallest among the prepared catalysts,which is corresponded with the CO chemisorp-tion results.The particle size decreased with an increase of Sn content on Pt0.5(Table4).The average Pt particles size by HRTEM analysis was approximately half of that from the chemisorption data(Table4),when a conventional CO/Pt atm of1.0was used for the Pt particle size calculation.In the supported Pt/Al2O3catalysts, the CO/H ratio for a Pt atom was estimated at0.83–0.96[50].In the well-dispersed catalysts,a CO/H ratio of0.7was reported for an H/Pt ratio of1.0,which was due to the CO bridged bonding of50% on Pt[51].Here,the metal particle sizes of the bimetallic catalysts by HRTEM analysis is equivalent to those by CO chemisorption,if the CO/Pt ratio is0.5.

3.2.Catalytic activity

The alkane dehydrogenation reaction has been carried out in vapor phase at atmospheric pressure.In order to understand the catalytic activity,the individual(propane and n-butane)alkane dehydrogenation reaction was studied on Pt0.5,Sn0.75,(PtSn)0.5, Pt0.5Sn0.75,Pt0.5Sn1.0and Pt0.5Sn1.5catalysts.The propane dehy-drogenation reaction was carried out at873–923K and n-butane dehydrogenation reaction was at823–873K for5h.

3.2.1.Propane dehydrogenation reaction

3.2.1.1.Effect of Sn content on0.5wt%Pt/?-Al2O3.Fig.5shows the propane conversion with respect to the reaction time on the calcined Pt0.5Sn x.x catalysts with different Sn content.The propane dehydrogenation reaction was carried out at873K for 5h.The monometallic Pt0.5and Sn0.75catalyst showed very low conversion with time on stream.In bimetallic catalyst,the conversion of propane increased with the Sn loading up to 0.75wt%of Sn.The conversion was drastically decreased on the Pt0.5Sn1.5catalyst.The initial conversions of Pt0.5,(PtSn)0.5, Pt0.5Sn0.75,Pt0.5Sn1.0,and Pt0.5Sn1.5catalyst were18.1,28.3,28.8, 22.6,and17.5%,respectively.The conversions of each catalyst after5h decreased to12.2,23.7,25.5,19.9and13.5%,respec-tively.The conversion of the Pt0.5Sn0.75catalyst was not only the highest among the prepared catalysts,but also the most stable.The catalyst listed in order of both the propane conver-sion and the C3yield of the catalysts at873K was as follows: Pt0.5Sn0.75>(PtSn)0.5>Pt0.5Sn1.0>Pt0.5Sn1.5>Pt0.5>Sn0.75.

Table4shows the propane conversion,C3selectivity and yields,and deactivation parameters.The initial and?nal conver-sion of the(PtSn)0.5catalyst were28.3and23.7%,respectively.The C3yield of the(PtSn)0.5catalyst was better than that of Pt0.5Sn1.0 sample,but the catalyst was severely deactivated with time on stream(deactivation parameter=16.2).The metal surface area of the(PtSn)0.5catalyst was lower than that of Pt0.5Sn1.0,but the ini-tial activity of the Pt0.5Sn0.5catalyst was higher than that of the Pt0.5Sn1.0.As rules,the Pt surface composition on the Pt0.5Sn1.0cat-alyst can be lower than that of the(PtSn)0.5catalyst.Therefore, it can be proposed that alkane dehydrogenation activity can be related to the Pt surface composition as well as the Pt surface area, which can be related to the geometric effects.The TPR pattern of the(PtSn)0.5catalyst was similar to that of the Pt0.5,resulting in large particle size.This was con?rmed by CO chemisorption and HRTEM analysis as shown in Table3.The highest Pt concentra-tion on the surface of the(PtSn)0.5catalysts among the bimetallic

M.-H.Lee et al./Catalysis Today 232(2014)

53–62

Fig.4.HRTEM images and particle size distribution of the reduced Pt 0.5Sn x .x /?-Al 2O 3catalysts with different Sn contents:(a and a1)Pt 0.5,(b and b1)(PtSn)0.5,(c and c1)Pt 0.5Sn 0.75,(d and d1)Pt 0.5Sn 1.0and (e and e1)Pt 0.5Sn 1.5.

catalysts resulted in the severe deactivation.The Pt 0.5Sn 0.75showed the highest yield and stability,because of the highest Pt dispersion and the proper Pt surface concentration on the PtSn alloy.Further increase in the Sn concentration (Pt 0.5Sn 1.5)caused a decrease in the activity of the catalysts.As discussed previously,the encapsu-lation of Pt by Sn can occur with Pt 0.5Sn 1.5,resulting in an increase of the PtSn particle size.Therefore,the Pt 0.5Sn 0.75catalyst had the smallest particle size among the prepared catalysts,showing

the highest activity as well as the highest stability for propane dehydrogenation.

3.2.1.2.Effect of reaction temperature and stability test on Pt 0.5Sn 0.75catalyst.Fig.6shows the propane conversion of Pt 0.5Sn 0.75cata-lyst with respect to the time on stream in the range of 873–923K,and Table 5shows the deactivation parameter,propane conversion,C 3selectivity,and C 3yield.The deactivation parameter increased

M.-H.Lee et al./Catalysis Today 232(2014)53–62

Table 4

Activity (conversion,selectivity and yield)and deactivation parameter of Pt 0.5Sn x .x /?-Al 2O 3catalysts with different Sn contents for propane dehydrogenation.

Catalysts (wt%)

Conversion (%)

Deactivation parameter a , X

Selectivity,S i /S f (%)

Yield of C 3,Y f (%)

Initial,X i

Final,X f

C 1–C 2

C 3

Others

(PtSn)0.528.323.716.2 4.2/4.989.4/90.5 6.4/4.621.4Pt 0.5Sn 0.7528.825.511.4 3.1/4.291.4/91.0 5.5/4.823.2Pt 0.5Sn 1.022.619.911.9 6.6/7.886.3/86.67.1/5.617.2Pt 0.5Sn 1.517.513.522.97.7/10.487.4/85.4 4.8/4.311.5Pt 0.518.112.232.68.2/10.086.7/86.0 5.1/4.010.5Sn 0.75

4.9

5.5

–

31.4/39.2

55.8/49.9

12.8/10.9

2.7

X =(X i ?X f )/X i ×100.

Table 5

Activity (conversion,selectivity and yield)and deactivation parameter of Pt 0.5Sn 0.75supported ?-Al 2O 3catalyst with different reaction temperatures for propane dehydrogenation.

Temperature (K)

Conversion (%)

Deactivation parameter, X

Selectivity,S i /S f (%)

Yield of C 3,Y f (%)

Initial,X i

Final,X f

C 1–C 2

C 3

Others

87328.825.511.5 3.1/4.291.4/91.0 5.5/4.823.289836.929.819.2 5.8/7.884.4/85.09.8/7.225.3923

37.4

25.4

32.1

7.5/16.7

84.4/73.9

8.2/9.4

18.8

Time on strea

m (min. )

C o n v e r s i o n (%)

Fig.5.Conversion vs.time on stream on Pt 0.5Sn x .x /?-Al 2O 3catalyst with different

Sn contents for the propane dehydrogenation (Reaction condition:catalyst weight –0.08g,reduction temperature –883K/2h,reaction temperature –873K/5h,C 3H 8:H 2–3:2,total ?ow rate –30mL min ?1).

C o n v e r s i o n (%)

Time on stream (min. )

Fig.6.Conversion vs.time on stream on Pt 0.5Sn 0.75catalyst with different temper-atures for the propane dehydrogenation;reaction conditions as in Fig.5.

with an increase in the reaction temperature.The cracking products of C 1–C 2and other bi-products also increased with an increase in the reaction temperature,resulting in the low C 3selectivity.The initial and ?nal conversion at 873K was 28.8and 25.5%,respectively and the C 3yield was 23.2%.The initial conversion of propane at 898and 923K was high,but the catalyst was signi?cantly deacti-vated after 5h.Therefore,it can be concluded that the temperature of about 873K was appropriate for propane dehydrogenation on the Pt 0.5Sn 0.75catalyst.

Fig.7shows the time-dependent catalytic activity of the Pt 0.5Sn 0.75catalyst in propane dehydrogenation.The reaction was carried out at 873K for 15h.This catalyst was slightly deactivated with time on stream.The initial and ?nal conversions were 28.8and 22.9%,respectively,and the deactivation parameter was 20.5over an operation period of 15h.The initial and ?nal selectivity of propylene was 91.4and 89.5%,respectively,and the C 3yield was 20.5%after 15h at 873K.

3.3.n-butane dehydrogenation reaction

3.3.1.1.Effect of Sn content on 0.5wt%Pt/?-Al 2O 3

Fig.8shows the conversion of n-butane with respect to the reaction time on the Pt 0.5,Sn 0.75,and bimetallic catalysts with different Pt 0.5Sn x .x with different Sn content supported on ?-Al 2O 3.

C o n v e r s i o n (%)

S e l e c t i v i t y (%)

Time on strea m (min .)

Fig.7.Stability test on Pt 0.5Sn 0.75catalyst at 873K for 15h for the propane dehy-drogenation;reaction conditions as in Fig.5.

M.-H.Lee et al./Catalysis Today 232(2014)53–62

Table 6

Activity (conversion,selectivity and yield)and deactivation parameter of Pt 0.5Sn x .x /?-Al 2O 3catalysts with different Sn contents for n-butane dehydrogenation.

Catalysts (wt%)

Conversion (%)

Deactivation parameter, X

Selectivity (S i /S f )(%)

Yield of n-C 4,Y f (%)

Initial,X i

Final,X f C 1–C 3n-C 4i-C 4

1,3-Butadiene

1-Butene

2-Butene

(PtSn)0.541.933.121.0 2.3/2.733.3/34.550.4/52.410.1/5.8 3.9/4.428.1Pt 0.5Sn 0.7544.537.515.7 1.7/1.733.5/35.151.7/53.99.1/4.8 4.0/4.533.2Pt 0.5Sn 1.043.337.214.0 1.3/1.634.9/36.052.2/54.07.7/4.3 3.8/4.233.5Pt 0.5Sn 1.540.031.321.8 1.9/2.335.0/35.352.6/53.5 6.4/4.5 4.1/4.527.8Pt 0.510.77.827.18.5/10.030.0/29.747.1/45.610.0/10.0 4.3/4.6 5.8Sn 0.75 1.6

1.7

–

40.9/38.3

10.4/11.7

15.8/17.0

32.9/31.8

0.0/1.2

0.8

The n-butane dehydrogenation was carried out at 823K for 5h.The monometallic Pt 0.5and Sn 0.75catalyst showed very low conver-sion with time on stream.The initial conversions of Pt 0.5,(PtSn)0.5,Pt 0.5Sn 0.75,Pt 0.5Sn 1.0,and Pt 0.5Sn 1.5catalyst were 27.1,41.9,44.5,43.3,and 40.0%,respectively.The conversions of each catalyst after 5h decreased to 7.8,33.1,37.5,37.2,and 31.3%,respec-tively.The Pt 0.5Sn 0.75catalyst showed the highest initial activity in both propane and n-butane dehydrogenation.On the other hand,the Pt 0.5Sn 1.0catalyst showed the most stability in n-butane dehydrogenation,while the Pt 0.5Sn 0.75catalyst in propane dehy-drogenation.

Table 6shows the initial and ?nal conversion (X i and X f ,mea-sured at 30to 300min,time on stream),n-C 4selectivity,and n-C 4yield of the Pt 0.5,Sn 0.75,and Pt 0.5Sn x .x catalysts.Similarly to propane dehydrogenation,the catalytic activity is closely related to the Pt metal dispersion.In that point,the Pt 0.5Sn 0.75catalyst also showed the highest initial activity in n-butane dehydrogenation,which is due to the high metal dispersion (18.3%)and metal surface area (0.226m 2(g cat ?1),and small particles of Pt (<6.2nm)(Table 3).Veldurthi et al.reported that the improvement of catalytic activity was mainly related to the metal dispersion,metal surface area,and particle size of the catalysts [54].

The selectivity to 1,3-butandiene was limited by the thermody-namic equilibrium in the reaction condition.The products of C 1–C 3included methane,ethane,propane,and propylene,which could be produced on the hydro cracking sites on Pt catalysts.However,the selectivity to C 1–C 3on the Pt 0.5Sn x .x bimetallic catalysts was much low as compared with that of the Pt 0.5catalyst,indicating that the hydro cracking sites were blocked by the Sn addition.On the other hand,the i-C 4selectivity gives the information on the

C o n v e r s i o n (%)

Time on str eam (min.)

Fig.8.Conversion vs.time on stream on Pt 0.5Sn x .x /?-Al 2O 3catalyst with different Sn

contents for the n-butane dehydrogenation (Reaction condition:catalyst weight –0.1g,reduction temperature –823K/2h,reaction temperature –823K/5h,H 2:N 2:n-C 4H 10–1:1:1,total ?ow rate –30mL min ?1).

isomerization sites.The experimental data showed that the Sn addi-tion slightly suppressed the isomerization sites.The high selectivity of the bimetallic catalysts could have been due to the electronic or geometric effects of PtSn alloy particles [50,55,38].The activity of the prepared catalysts were correlated with the Pt metal dis-persion and the PtSn alloy formation from XRD,TPR,HRTEM and CO chemisorption studies,assuming that the surface composition of Pt and Sn on the PtSn alloy were closely related to the cata-lyst composition.The alloy particles restrict the sites for cracking,hydrogenolysis,and isomerization,resulting in high n-C 4selec-tivity and resistance to the coke formation [56].

The deactivation parameters of mono-and bimetallic catalysts are also shown in Table 6( X =100×(X i ?X f )/X i ,where X i is the initial and X f is the ?nal conversion,respectively).The bimetallic Pt 0.5Sn 1.0catalyst was the most stable with time on stream at 823K for 5h (deactivation parameter =14.0)in n-butane dehydrogena-tion,while the Pt 0.5Sn 0.75catalyst was in propane dehydrogenation.The catalyst listed in order of propylene yield at 873K was as follows:Pt 0.5Sn 0.75>(PtSn)0.5>Pt 0.5Sn 1.0>Pt 0.5Sn 1.5,while that in order of n-butenes yield was as follows:Pt 0.5Sn 1.0>Pt 0.5Sn 0.75>(PtSn)0.5>Pt 0.5Sn 1.5.The results suggest that the optimized Pt and Sn

composition for alkane dehydrogena-tion can be dependent on the carbon number and the structure of the saturated hydrocarbon as well as the Pt metal surface areas.

3.3.1.2.Effect of reaction temperature and stability test on Pt 0.5Sn 0.75catalyst

For the comparison with propane dehydrogenation,Fig.9shows the n-butane conversion of Pt 0.5Sn 0.75catalyst with respect to the time on stream in the range of 773–873K,and Table 7shows the deactivation parameter,n-butane conversion,n-C 4selectivity,and n-C 4yield.The deactivation parameters at 773,823,and 873K

C o n v e r s i o n (%)

Time on stream (min.)

Fig.9.Conversion vs.time on stream on Pt 0.5Sn 0.75catalyst with different temper-atures for the n-butane dehydrogenation;reaction conditions as in Fig.8.

M.-H.Lee et al./Catalysis Today 232(2014)53–62

Table 7

Activity (conversion,selectivity and yield)and deactivation parameter of Pt 0.5Sn 0.75/?-Al 2O 3catalyst with different temperatures for n-butane dehydrogenation reaction.

Temperature (K)

Conversion (%)

Deactivation parameter, X

Selectivity (S i /S f )(%)

Yield of n-C 4,Y f (%)

Initial,X i

Final,X f C 1–C 3n-C 4i-C 4

1,3-butadiene

1-Butene

2-Butene

7739.27.221.7 5.7/7.133.5/31.950.5/49.6 4.7/5.7 5.6/5.7 5.982344.537.515.7 1.7/1.733.5/35.151.7/53.99.1/4.8 4.0/4.533.4873

53.4

32.5

39.1

6.2/10.0

27.2/28.2

43.8/46.2

8.6/10.7

14.2/4.9

24.2

S e l e c t i v i t y (%)

C o n v e r s i o n (%)

Time on str eam (min.)

Fig.10.Stability test on Pt 0.5Sn 0.75catalyst at 823K for 15h for the n-butane dehy-drogenation;reaction conditions as in Fig.8.

were 21.7,15.7and 32.5,respectively.The catalyst was rapidly

deactivated at 873K.The cracking products of C 1–C 3and i-C 4at 873K was very high among the other temperatures,resulting in the low n-C 4selectivity.The higher the reaction temperature,the higher the 1,3-butadiene yield in the thermodynamic point.The Pt 0.5Sn 0.75catalyst at 823K showed the highest n-C 4yield,n-C 4selectivity and low deactivation parameter in n-butane dehydro-genation reaction

Fig.10shows the time-dependent catalytic activity (conversion and selectivity)of the Pt 0.5Sn 0.75catalyst.The reaction was carried out at 823K for 15h.The Pt 0.5Sn 0.75catalyst was slightly deacti-vated at 823K for 15h in n-butane dehydrogenation reaction.The initial and ?nal conversion was 44.5and 26.8%,respectively and the deactivation rate was 39.8after 15h.The initial and ?nal selec-tivity of 1-butene and 2-butene were 33.5/36.1and 51.7/54.5%,respectively.The selectivity of cracking products was not so much changed with time on stream.The experimental results show that the stability of the PtSn catalyst in propane dehydrogenation is much higher than that in n-butane dehydrogenation.

4.Conclusions

The Pt 0.5Sn x .x /?-Al 2O 3catalysts with different Sn contents (x .x =0.5,0.75,1.0and 1.5)were studied for propane and n-butane dehydrogenation.XRD showed the PtSn alloy phases with the (PtSn)0.5and Pt 0.5Sn 1.5catalysts,clearly.However,the PtSn phases with the Pt 0.5Sn 0.75and Pt 0.5Sn 1.0catalysts were rarely observed,which was attributed to the small particle sizes.The particle sizes of the prepared catalysts were measured with the CO chemisorption and HRTEM.The metal particle sizes of the Pt 0.5Sn 0.75and Pt 0.5Sn 1.0catalysts were small as compared with those of the (PtSn)0.5and Pt 0.5Sn 1.5catalysts.In TPR analysis,the small particle sizes of the Pt 0.5Sn 0.75and Pt 0.5Sn 1.0cata-lysts were attributed to the co-reduction of Pt and Sn at low temperature.The propane dehydrogenation was carried out at 873K for 5h,while the n-butane dehydrogenation was car-ried out at 823K for 5h.The catalyst in propylene yield was

in the order of Pt 0.5Sn 0.75>(PtSn)0.5>Pt 0.5Sn 1.0>Pt 0.5Sn 1.5,while that in n-butenes yield was in the order of Pt 0.5Sn 1.0>Pt 0.5Sn 0.75>(PtSn)0.5>Pt 0.5Sn 1.5.The Pt 0.5Sn 1.5cat-alyst showed the lowest ole?n yields among the prepared bimetallic catalysts in both propane and n-butane dehydrogena-tion.The lowest activity of the Pt 0.5Sn 1.5catalyst was due to the encapsulation of Sn on Pt particles at the high Sn concentration.The encapsulation resulted in low Pt metal surface area.The metal surface area of the (PtSn)0.5catalyst was lower than that of Pt 0.5Sn 1.0,but the activity of the Pt 0.5Sn 0.5catalyst was higher than that of the Pt 0.5Sn 1.0catalyst in propane dehydrogenation.As rules,the Pt surface composition on the Pt 0.5Sn 1.0catalyst can be lower than that of the (PtSn)0.5catalyst.Therefore,it can be proposed that alkane dehydrogenation activity can be related to the Pt surface composition on the PtSn alloy as well as the Pt metal surface area,which can be related to the geometric effects.In n-butane dehydrogenation,the catalytic activity of the PtSn bimetallic catalysts was dependent on the Pt metal surface areas.The Pt 0.5Sn 0.75catalyst showed the highest initial activity in both propane and n-butane dehydrogenation.On the other hand,the Pt 0.5Sn 1.0catalyst showed the most stability in n-butane dehydrogenation,while the Pt 0.5Sn 0.75catalyst in propane dehy-drogenation.In alkane dehydrogenation,the addition of Sn to Pt catalyst did not only suppress the cracking sites of the Pt catalysts to increase the ole?n selectivity,but also increased the Pt metal surface areas to increase the catalytic activity at the Pt/Sn weight ratio lower than 3.0.

Acknowledgement

This work was supported by the basic research project of KIST and by Converging Research Center Program through the National Research Foundation of Korea (NRF)funded by the Ministry of Edu-cation,Science and Technology (2011K000660).

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牛人教你如何阅读外文文献 2015-04-16 22:40 来源：科学网点击次数：5085关键词：英文文献一、如何有针对地查找文献？现在各大学图书馆里的数据库都比较全，即使不全也可以通过网络上多种手段获取文献了。所以说文献的获取不是问题，问题在于查什么样的文献？ 1）本领域核心期刊的文献。不同的研究方向有不同的核心期刊，这里也不能一概唯IF论了。当然，首先你要了解所研究的核心期刊有哪些，这个就要靠学长、老板或者网上战友的互相帮助了。 2）本领域牛人或主要课题组的文献。每个领域内都有几个领军人物，他们所从事的方向往往代表目前的发展主流。因此，阅读这些组里的文献就可以把握目前的研究重点。怎么知道谁是“领军人物”呢？这里提供两个小方法：第一，在ISI里检索本领域的文献，利用refine 功能找出论文数量较多的作者或课题组；另一个方法，先要了解本领域有哪些比较规模大型的国际会议，登陆会议主办方的网站一般都能看到关于会议的invited speaker的名字，作为邀请报告的报告人一般就是了。 3）高引用次数的文章。一般来说高引用次数（如果不是靠自引堆上去的话）文章都是比较经典的文章。多读这样的文章，体会作者对文章结构的把握和图表分析的处理，相信可以从中领悟很多东西。知道了查什么样的文献后，那么具体怎么去查文献？ ?通过关键词、主题词检索：关键词、主题词一定要选好，这样，才能保证你所要的内容的全面。因为，换个主题词，可以有新的内容出现。 ?通过检索某个学者：查SCI，知道了某个在这个领域有建树的学者，找他近期发表的文章。 ?通过参考综述检索：如果有与自己课题相关或有切入点的综述，可以根据相应的参考文献找到那些原始的研究论文。

五、外文资料翻译 Stress and Strain 1.Introduction to Mechanics of Materials Mechanics of materials is a branch of applied mechanics that deals with the behavior of solid bodies subjected to various types of loading. It is a field of study that i s known by a variety of names, including “strength of materials” and “mechanics of deformable bodies”. The solid bodies considered in this book include axially-loaded bars, shafts, beams, and columns, as well as structures that are assemblies of these components. Usually the objective of our analysis will be the determination of the stresses, strains, and deformations produced by the loads; if these quantities can be found for all values of load up to the failure load, then we will have obtained a complete picture of the mechanics behavior of the body. Theoretical analyses and experimental results have equally important roles in the study of mechanics of materials . On many occasion we will make logical derivations to obtain formulas and equations for predicting mechanics behavior, but at the same time we must recognize that these formulas cannot be used in a realistic way unless certain properties of the been made in the laboratory. Also , many problems of importance in engineering cannot be handled efficiently by theoretical means, and experimental measurements become a practical necessity. The historical development of mechanics of materials is a fascinating blend of both theory and experiment, with experiments pointing the way to useful results in some instances and with theory doing so in others①. Such famous men as Leonardo da Vinci(1452-1519) and Galileo Galilei (1564-1642) made experiments to adequate to determine the strength of wires , bars , and beams , although they did not develop any adequate theo ries (by today’s standards ) to explain their test results . By contrast , the famous mathematician Leonhard Euler(1707-1783) developed the mathematical theory any of columns and calculated the critical load of a column in 1744 , long before any experimental evidence existed to show the significance of his results ②. Thus , Euler’s theoretical results remained unused for many years, although today they form the basis of column theory. The importance of combining theoretical derivations with experimentally determined properties of materials will be evident theoretical derivations with experimentally determined properties of materials will be evident as we proceed with

中文参考文献格式参考文献（即引文出处）的类型以单字母方式标识： M——专著，C——论文集，N——报纸文章，J——期刊文章，D——学位论文，R——报告，S——标准，P——专利；对于不属于上述的文献类型，采用字母“Z”标识。参考文献一律置于文末。其格式为：（一）专著示例 [1] 张志建.严复思想研究[M]. 桂林：广西师范大学出版社，1989. [2] 马克思恩格斯全集：第1卷[M]. 北京：人民出版社，1956. [3] [英]蔼理士.性心理学[M]. 潘光旦译注.北京：商务印书馆，1997. （二）论文集示例 [1] 伍蠡甫.西方文论选[C]. 上海：上海译文出版社，1979. [2] 别林斯基.论俄国中篇小说和果戈里君的中篇小说[A]. 伍蠡甫.西方文论选：下册[C]. 上海：上海译文出版社，1979. 凡引专著的页码，加圆括号置于文中序号之后。（三）报纸文章示例 [1] 李大伦.经济全球化的重要性[N]. 光明日报，1998-12-27，（3）（四）期刊文章示例 [1] 郭英德.元明文学史观散论[J]. 北京师范大学学报（社会科学版），1995（3）. （五）学位论文示例 [1] 刘伟.汉字不同视觉识别方式的理论和实证研究[D]. 北京：北京师范大学心理系，1998. （六）报告示例 [1] 白秀水，刘敢，任保平. 西安金融、人才、技术三大要素市场培育与发展研究[R]. 西安：陕西师范大学西北经济发展研究中心，1998. （七）、对论文正文中某一特定内容的进一步解释或补充说明性的注释，置于本页地脚，前面用圈码标识。参考文献的类型根据GB3469-83《文献类型与文献载体代码》规定，以单字母标识： M——专著（含古籍中的史、志论著） C——论文集 N——报纸文章 J——期刊文章 D——学位论文 R——研究报告 S——标准 P——专利 A——专著、论文集中的析出文献 Z——其他未说明的文献类型电子文献类型以双字母作为标识： DB——数据库 CP——计算机程序 EB——电子公告

(文档含英文原文和中文翻译) 中英文翻译平面设计任何时期平面设计可以参照一些艺术和专业学科侧重于视觉传达和介绍。采用多种方式相结合，创造和符号，图像和语句创建一个代表性的想法和信息。平面设计师可以使用印刷，视觉艺术和排版技术产生的最终结果。平面设计常常提到的进程，其中沟通是创造和产品设计。共同使用的平面设计包括杂志，广告，产品包装和网页设计。例如，可能包括产品包装的标志或其他艺术作品，举办文字和纯粹的设计元素，如形状和颜色统一件。组成的一个最重要的特点，尤其是平面设计在使用前现有材料或不同的元素。平面设计涵盖了人类历史上诸多领域，在此漫长的历史和在相对最近爆炸视觉传达中的第20和21世纪，人们有时是模糊的区别和重叠的广告艺术，平面设计和美术。毕竟，他们有着许多相同的内容，理论，原则，做法和语言，有时同样的客人或客户。广告艺术的最终目标是出售的商品和服务。在平面

设计，“其实质是使以信息，形成以思想，言论和感觉的经验”。在唐朝（ 618-906 ）之间的第4和第7世纪的木块被切断打印纺织品和后重现佛典。阿藏印在868是已知最早的印刷书籍。在19世纪后期欧洲，尤其是在英国，平面设计开始以独立的运动从美术中分离出来。蒙德里安称为父亲的图形设计。他是一个很好的艺术家，但是他在现代广告中利用现代电网系统在广告、印刷和网络布局网格。于1849年，在大不列颠亨利科尔成为的主要力量之一在设计教育界，该国政府通告设计在杂志设计和制造的重要性。他组织了大型的展览作为庆祝现代工业技术和维多利亚式的设计。从1892年至1896年威廉?莫里斯凯尔姆斯科特出版社出版的书籍的一些最重要的平面设计产品和工艺美术运动，并提出了一个非常赚钱的商机就是出版伟大文本论的图书并以高价出售给富人。莫里斯证明了市场的存在使平面设计在他们自己拥有的权利，并帮助开拓者从生产和美术分离设计。这历史相对论是，然而，重要的，因为它为第一次重大的反应对于十九世纪的陈旧的平面设计。莫里斯的工作，以及与其他私营新闻运动，直接影响新艺术风格和间接负责20世纪初非专业性平面设计的事态发展。谁创造了最初的“平面设计”似乎存在争议。这被归因于英国的设计师和大学教授Richard Guyatt，但另一消息来源于20世纪初美国图书设计师William Addison Dwiggins。伦敦地铁的标志设计是爱德华约翰斯顿于1916年设计的一个经典的现代而且使用了系统字体设计。在20世纪20年代，苏联的建构主义应用于“智能生产”在不同领域的生产。个性化的运动艺术在俄罗斯大革命是没有价值的，从而走向以创造物体的功利为目的。他们设计的建筑、剧院集、海报、面料、服装、家具、徽标、菜单等。 Jan Tschichold 在他的1928年书中编纂了新的现代印刷原则，他后来否认他在这本书的法西斯主义哲学主张，但它仍然是非常有影响力。 Tschichold ，包豪斯印刷专家如赫伯特拜耳和拉斯洛莫霍伊一纳吉，和El Lissitzky 是平面设计之父都被我们今天所知。他们首创的生产技术和文体设备，主要用于整个二十世纪。随后的几年看到平面设计在现代风格获得广泛的接受和应用。第二次世界大战结束后，美国经济的建立更需要平面设计，主要是广告和包装等。移居国外的德国包豪斯设计学院于1937年到芝加哥带来了“大规模生产”极简到美国;引发野火的“现代”建筑和设计。值得注意的名称世纪中叶现代设计包括阿德里安Frutiger ，设计师和Frutiger字体大学;保兰德，从20世纪30年代后期，直到他去世于1996年，采取的原则和适用包豪斯他们受欢迎的广告和标志设计，帮助创造一个独特的办法，美国的欧洲简约而成为一个主要的先驱。平面设计称为企业形象;约瑟夫米勒，罗克曼，设计的海报严重尚未获取1950年代和1960年代时代典型。从道路标志到技术图表，从备忘录到参考手册，增强了平面设计的知识转让。可读性增强了文字的视觉效果。设计还可以通过理念或有效的视觉传播帮助销售产品。将它应用到产品和公司识别系统的要素像标志、颜色和文字。连同这些被定义为品牌。品牌已日益成为重要的提供的服务范围，许多平面设计师，企业形象和条件往往是同时交替使用。

在广州甚至广东的住宅小区电气设计中,一般都会涉及到小区的高低压供配电系统的设计.如10kV高压配电系统图,低压配电系统图等等图纸一大堆.然而在真正实施过程中,供电部门(尤其是供电公司指定的所谓电力设计小公司)根本将这些图纸作为一回事,按其电脑里原有的电子档图纸将数据稍作改动以及断路器按其所好换个厂家名称便美其名曰设计(可笑不?),拿出来的图纸根本无法满足电气设计的设计意图,致使严重存在以下问题:(也不知道是职业道德问题还是根本一窍不通) 1.跟原设计的电气系统货不对板,存在与低压开关柜后出线回路严重冲突,对实际施工造成严重阻碍,经常要求设计单位改动原有电气系统图才能满足它的要求(垄断的没话说). 2.对消防负荷和非消防负荷的供电(主要在高层建筑里)应严格分回路(从母线段)都不清楚,将消防负荷和非消防负荷按一个回路出线(尤其是将电梯和消防电梯,地下室的动力合在一起等等,有的甚至将楼顶消防风机和梯间照明合在一个回路,以一个表计量). 3.系统接地保护接地型式由原设计的TN-S系统竟曲解成"TN-S-C-S"系统(室内的还需要做TN-C,好玩吧?),严格的按照所谓的"三相四线制"再做重复接地来实施,导致后续施工中存在重复浪费资源以及安全隐患等等问题.. ............................(违反建筑电气设计规范等等问题实在不好意思一一例举,给那帮人留点混饭吃的面子算了) 总之吧,在通过图纸审查后的电气设计图纸在这帮人的眼里根本不知何物,经常是完工后的高低压供配电系统已是面目全非了,能有百分之五十的保留已经是谢天谢地了. 所以.我觉得:住宅建筑电气设计,让供电部门走!大不了留点位置,让他供几个必需回路的电,爱怎么折腾让他自个怎么折腾去.. Guangzhou, Guangdong, even in the electrical design of residential quarters, generally involving high-low cell power supply system design. 10kV power distribution systems, such as maps, drawings, etc. low-voltage distribution system map a lot. But in the real implementation of the process, the power sector (especially the so-called power supply design company appointed a small company) did these drawings for one thing, according to computer drawings of the original electronic file data to make a little change, and circuit breakers by their the name of another manufacturer will be sounding good design (ridiculously?), drawing out the design simply can not meet the electrical design intent, resulting in a serious following problems: (do not know or not know nothing about ethical issues) 1. With the original design of the electrical system not meeting board, the existence and low voltage switchgear circuit after qualifying serious conflicts seriously hinder the actual construction, often require changes to the original design unit plans to meet its electrical system requirements (monopoly impress ). 2. On the fire load and fire load of non-supply (mainly in high-rise building in) should be strictly sub-loop (from the bus segment) are not clear, the fire load and fire load of non-qualifying press of a circuit (especially the elevator and fire elevator, basement, etc.

毕业设计说明书英文文献及中文翻译学院：专 2011年6月电子与计算机科学技术软件工程

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一.看国外文献的方法总结（从PhD到现在工作半年，发了12 篇paper，7 篇first author.）我现在每天还保持读至少2-3 篇的文献的习惯.读文献有不同的读法.但最重要的自己总结概括这篇文献到底说了什么,否则就是白读,读的时候好像什么都明白,一合上就什么都不知道,这是读文献的大忌,既浪费时间,最重要的是,没有养成良好的习惯,导致以后不愿意读文献. 1. 每次读完文献 (不管是细读还是粗读), 合上文献后,想想看,文章最重要的take home message 是什么, 如果不知道,就从abstract,conclusion 里找, 并且从discuss 里最好确认一下. 这样一来, 一篇文章就过关了. take home message 其实都不会很多, 基本上是一些concepts, 如果你发现你需要记得很多,那往往是没有读到重点. 2. 扩充知识面的读法, 重点读introduction, 看人家提出的问题,以及目前的进展类似的文章, 每天读一两篇,一个月就基本上对这个领域的某个方向有个大概的了解.读好的review 也行, 但这样人容易懒惰. 3. 为了写文章的读法, 读文章的时候, 尤其是看discussion 的时候,看到好的英文句型, 最好有意识的记一下,看一下作者是谁,哪篇文章,哪个期刊, 这样以后照猫画虎写的时候,效率高些.比自己在那里半天琢磨出一个句子强的多. 当然,读的多,写的多,你需要记得句型就越少.其实很简单,有意识的去总结和记亿, 就不容易忘记.

二．研究生怎么看文献，怎么写论文先读综述,可以更好地认识课题,知道已经做出什么，自己要做什么,,还有什么问题没有解决。对于国文献一般批评的声音很多.但它是你迅速了解你的研究领域的入口,在此之后,你再看外文文献会比一开始直接看外文文献理解的快得多。而国外的综述多为本学科的资深人士撰写，涉及围广，可以让人事半功倍。针对你自己的方向,找相近的论文来读,从中理解文章中回答什么问题,通过哪些技术手段来证明,有哪些结论?从这些文章中,了解研究思路,逻辑推论,学习技术方法. 1.关键词、主题词检索：关键词、主题词一定要选好，这样，才能保证你所要的容的全面。因为，换个主题词，可以有新的容出现。 2. 检索某个学者：查SCI,知道了某个在这个领域有建树的学者，找他近期发表的文章。3. 参考综述检索：如果有与自己课题相关或有切入点的综述，可以根据相应的参考文献找到那些原始的研究论文。 4. 注意文章的参考价值：刊物的影响因子、文章的被引次数能反映文章的参考价值。但要注意引用这篇文章的其它文章是如何评价这篇文章的

International Journal of Minerals, Metallurgy and Materials Volume 17, Number 4, August 2010, Page 500 DOI: 10.1007/s12613-010-0348-y Corresponding author: Zhuan Li E-mail: li_zhuan@https://www.wendangku.net/doc/e718098043.html, ? University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg 2010 Preparation and properties of C/C-SiC brake composites fabricated by warm compacted-in situ reaction Zhuan Li, Peng Xiao, and Xiang Xiong State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China (Received: 12 August 2009; revised: 28 August 2009; accepted: 2 September 2009) Abstract: Carbon fibre reinforced carbon and silicon carbide dual matrix composites (C/C-SiC) were fabricated by the warm compacted-in situ reaction. The microstructure, mechanical properties, tribological properties, and wear mechanism of C/C-SiC composites at different brake speeds were investigated. The results indicate that the composites are composed of 58wt% C, 37wt% SiC, and 5wt% Si. The density and open porosity are 2.0 g·cm–3 and 10%, respectively. The C/C-SiC brake composites exhibit good mechanical properties. The flexural strength can reach up to 160 MPa, and the impact strength can reach 2.5 kJ·m–2. The C/C-SiC brake composites show excellent tribological performances. The friction coefficient is between 0.57 and 0.67 at the brake speeds from 8 to 24 m·s?1. The brake is stable, and the wear rate is less than 2.02×10?6 cm3·J?1. These results show that the C/C-SiC brake composites are the promising candidates for advanced brake and clutch systems. Keywords: C/C-SiC; ceramic matrix composites; tribological properties; microstructure [This work was financially supported by the National High-Tech Research and Development Program of China (No.2006AA03Z560) and the Graduate Degree Thesis Innovation Foundation of Central South University (No.2008yb019).] 温压-原位反应法制备C / C-SiC刹车复合材料的工艺和性能李专，肖鹏，熊翔粉末冶金国家重点实验室，中南大学，湖南长沙410083，中国（收稿日期：2009年8月12日修订：2009年8月28日;接受日期：2009年9月2日）摘要：采用温压?原位反应法制备炭纤维增强炭和碳化硅双基体(C/C-SiC)复合材

关于毕业设计说明书（论文）英文文献及中文翻译撰写格式为提高我校毕业生毕业设计说明书（毕业论文）的撰写质量，做到毕业设计说明书（毕业论文）在内容和格式上的统一和规范，特规定如下: 一、装订顺序论文（设计说明书）英文文献及中文翻译内容一般应由3个部分组成，严格按以下顺序装订。 1、封面 2、中文翻译 3、英文文献（原文）二、书写格式要求 1、毕业设计（论文）英文文献及中文翻译分毕业设计说明书英文文献及中文翻译和毕业论文英文文献及中文翻译两种，所有出现相关字样之处请根据具体情况选择“毕业设计说明书” 或“毕业论文”字样。 2、毕业设计说明书（毕业论文）英文文献及中文翻译中的中文翻译用Word 软件编辑，英文文献用原文，一律打印在A4幅面白纸上，单面打印。 3、毕业设计说明书（毕业论文）英文文献及中文翻译的上边距:30mm；下边距:25mm；左边距:3Omm；右边距:2Omm；行间距1.5倍行距。 4、中文翻译页眉的文字为“中北大学2019届毕业设计说明书” 或“中北大学××××届毕业论文”，用小四号黑体字，页眉线的上边距为25mm；页脚的下边距为18mm。 5、中文翻译正文用小四号宋体，每章的大标题用小三号黑体，加粗，留出上下间距为：段前0.5行，段后0.5行；二级标题用小四号黑体，加粗；其余小标题用小四号黑体，不加粗。 6、文中的图、表、附注、公式一律采用阿拉伯数字分章编号。如图1.2，表2.3，附注3.2或式4.3。 7、图表应认真设计和绘制,不得徒手勾画。表格与插图中的文字一律用5号宋体。

每一插图和表格应有明确简短的图表名，图名置于图之下，表名置于表之上，图表号与图表名之间空一格。插图和表格应安排在正文中第一次提及该图表的文字的下方。当插图或表格不能安排在该页时，应安排在该页的下一页。图表居中放置，表尽量采用三线表。每个表应尽量放在一页内，如有困难，要加“续表X.X”字样，并有标题栏。图、表中若有附注时，附注各项的序号一律用阿拉伯数字加圆括号顺序排，如:注①。附注写在图、表的下方。文中公式的编号用圆括号括起写在右边行末顶格，其间不加虚线。 8、文中所用的物理量和单位及符号一律采用国家标准，可参见国家标准《量和单位》(GB3100~3102-93)。 9、文中章节编号可参照《中华人民共和国国家标准文献著录总则》。

英文专业文献导读》教学大纲课程编码：11272006 课程名称：英文专业文献导读英文名称：Introduction to Professional English Literature 开课学期：9 学时/学分：60/3 课程类型：专业课（选修）开课专业：信息管理与信息系统专业本科生选用教材：张强华等主编：《信息管理专业英语实用教程》，清华大学出版社，2005 年版。主要参考书： 1．祁延莉：《信息管理专业英语》，北京大学出版社，2005 年2 月第一版2．肖永英：《信息管理专业英语》，中国科技出版社，2001 年版。 3．李季方傅欣冯启华：《信息管理英语教程》，清华大学出版社，2004 年版执笔人：王丽伟一、课程性质、目的与任务专业英语是信息管理与信息系统专业为本科生开设的专业选修课程。在学生现有的英语语言技能和信息管理与信息系统专业知识的基础上，通过选用教材和有关课外材料的学习，使他们掌握信息管理与信息系统专业基本英语单词，掌握专业文献的内容特点和语言特色，在阅读实践中培养并提高他们理解和研究专业文献的能力，同时扩大和深化其语言和专业知识，增强语言运用能力和交流能力，并锻炼其逻辑思维能力。为将来的学术论文的阅读写作和交流打下坚实的基础。二、教学基本要求1．掌握信息管理专业英语的常用词汇、常用句型、风格和修辞手法； 2.准确理解这类文章中经常出现的信息管理概念和理论； 3.熟练阅读、正确理解信息管理专业英语，具备初步的独立分析能力； 4.通过有效的阅读训练，学会解读信息管理专业英语文献的段落大意和中心思想；在正确理解的基础上，撰写文章概要和与文章主题相关的小论文等； 5.进行信息管理专业英语文章的段落翻译（英译中），要求译文符合原义，行文顺畅；同时，进行一些中英句子翻译，主要目的是让学生学会信息管理专业英语文章中最常用的表达方法的实际运用。三、各章节内容及学时分配 Unit 1 （4 学时）教学目的与要求了解管理的作用和技巧，熟悉管理过程的四项基本职能：规划，组织，领导和控制。在语言文字方面，学生应当仔细阅读本单元文章，熟悉掌握管理专业英语的特点，包括相关的管理学词汇和用语，增强用准确流利的语言表达管理专业内容的能力。教学内容 1.管理背景知识介绍，进行与课文主题相关的问题讨论 2.课后所列专业术语(Special Terms) 3.课后所列短语的运用(Phrases) 4.分析课文难句，与学生讨论相关语法知识和难点，确保学生对文章内容的准确理解

Monolithic integrated circuit history The monolithic integrated circuit was born in the late-1970s, has experienced SCM, MCU, the SOC three big stages. SCM namely monolithic microcomputer (Single Chip Microcomputer) the stage, mainly seeks the best monolithic shape embedded system's best architecture. “the innovation pattern” obtains successfully, has established SCM and the general-purpose calculator completely different development path. In founds on the embedded system independent development path, Intel Corporation has lasting achievements. MCU namely micro controller (Micro Controller Unit) the stage, the main technological development direction is: Expands unceasingly when satisfies the embedded application, the object system request's each kind of peripheral circuit and the interface circuit, underline its object intellectualization control. It involves the domain is related with the object system, therefore, develops the MCU heavy responsibility to fall inevitably on electrical, the electronic technology factory. Looking from this angle, Intel fades out the MCU development also to have its objective factor gradually. Is developing the MCU aspect, the most famous factory family belongings count Philips Corporation. Philips Corporation by it in embedded application aspect huge superiority, MCS-51 from monolithic microcomputer rapidly expand to micro controller. Therefore, when we review the embedded system development path, do not forget Intel and the Philips historical merit. Monolithic integrated circuit is the embedded system's road of independent development, to the MCU stage development's important attribute, seeks application system's on chip maximized solution;

参考文献中英文人名的缩写规则参考文献是科技论文的重要组成部分，也是编辑加工和重要内容。温哥华格式要求，著录文后参考文献时，英文刊名和人名一律用缩写。这一规则也是众多检索系统在人名著录时的首选规则。下面我们先看一个例子：在文章发表时，由于西方人士名在前姓在后，一般也采用名+姓的格式书写，如下题名、作者及正文的书写： Bis-pyranoside Alkenes: Novel Templates for the Synthesis of Adjacently Linked Tetrahydrofurans Zheming Ruan, Phyllis Wilson and David R. Mootoo 而上述文章若作为参考文献为他人引用，则需写成 Bis-pyranoside Alkenes: Novel Templates for the Synthesis of Adjacently Linked Tetrahydrofurans Tetrahedron Letters Volume: 37, Issue: 21, May 2, 1996, pp. 3619-3622 Ruan, Zheming; Wilson, Phyllis; Mootoo, David R. 由于东西方姓与名排列的差异，有的国外杂志在人名后还给出作者学位或参加的学会，因此很多人不知道如何区别姓、名、学位单位，如何缩写。下面我们将著者姓名缩写规则的几个要点摘录如下： 1 姓名缩写只缩写名而不缩写姓； 2 无论东西方人，缩写名的书写形式都是姓在前、名在后； 3 杂志作者名中，全大写一定是姓； 4 省略所有缩写点如R. Brain Haynes缩写为Haynes RB, Edward J. Huth缩写为Huth EJ等。但有些特殊情况： (1)Maeve O'Conner, 正确缩写应为O'Conner M, 有人会按英文的构词习惯认为是印刷错误，认为Oconner M (2)国外也有复姓，如Julie C. Fanbury-Smith, Hartly Lorberboum-Galski等分别缩写为Fanbury-Smith JC, Lorbertoum-Galski HL (3)姓名中含前缀De,Des,Du,La,Dal,La,Von,Van,den,der等，将前缀和姓作为一个整体，按字顺排列，词间空格和大小写字母不影响排列，如Kinder Von Werder缩写为Von W erder K,不可写为Werder KV. (4)国外杂志要求作者署名后给出作者学位和加入的学会，学位与

看了大半年文献，没有什么经验，前几天去实验室和老板聊天，觉得自己看文献就像看历史书，呜呼！悲哉！无意间看到一篇文章觉得总结得不错，就与大家分享一下，觉得好就回复一个！ 1.牛人一（从phd到现在工作半年,发了12篇paper, 7篇first author.）我现在每天还保持读至少2-3篇的文献的习惯.读文献有不同的读法.但最重要的自己总结概括这篇文献到底说了什么,否则就是白读,读的时候好像什么都明白,一合上就什么都不知道,这是读文献的大忌,既浪费时间,最重要的是,没有养成良好的习惯,导致以后不愿意读文献. 1. 每次读完文献 (不管是细读还是粗读), 合上文献后,想想看,文章最重要的 take home message是什么, 如果不知道,就从abstract, conclusion里找, 并且从discuss里最好确认一下. 这样一来, 一篇文章就过关了. take home message其实都不会很多, 基本上是一些concepts, 如果你发现你需要记得很多,那往往是没有读到重点. 2. 扩充知识面的读法, 重点读introduction, 看人家提出的问题, 以及目前的进展类似的文章, 每天读一两篇,一个月内就基本上对这个领域的某个方向有个大概的了解.读好的review也行, 但这样人容易懒惰. 3. 为了写文章的读法, 读文章的时候, 尤其是看discussion的时候, 看到好的英文句型, 最好有意识的记一下,看一下作者是谁,哪篇文章,哪个期刊, 这样以后照猫画虎写的时候, 效率高些.比自己在那里半天琢磨出一个句子强的多. 当然,读的多,写的多,你需要记得句型就越少.其实很简单,有意识的去总结和记亿, 就不容易忘记. 2.牛人二科研牛人二告诉研究生怎么看文献，怎么写论文一、先看综述先读综述,可以更好地认识课题,知道已经做出什么，自己要做什么,,还有什么问题没有解决。对于国内文献一般批评的声音很多.但它是你迅速了解你的研究领域的入口,在此之后,你再看外文文献会比一开始直接看外文文献理解的快得多。而国外的综述多为本学科的资深人士撰写，涉及范围广，可以让人事半功倍。二、有针对地选择文献针对你自己的方向,找相近的论文来读,从中理解文章中回答什么问题,通过哪些技术手段来证明,有哪些结论?从这些文章中,了解研究思路,逻辑推论,学习技术方法. 1.关键词、主题词检索：关键词、主题词一定要选好，这样，才能保证你所要的内容的全面。因为，换个主题词，可以有新的内容出现。 2. 检索某个学者：查SCI,知道了某个在这个领域有建树的学者，找他近期发表的文章。 3. 参考综述检索：如果有与自己课题相关或有切入点的综述，可以根据相应的参考文献找到那些原始的研究论文。