XAFS應(yīng)用介紹

1、X射線吸收精細(xì)結(jié)構(gòu)譜XAFS（實驗方法和應(yīng)用）Web of Science Search: “EXAFS” or “XAFS”(but not “XAS” too many false hits) 1971-1975: 8 Publications Last year: 743 Publications Last 10 years: 7,199 Publications XAFS Beamline Design Parameter 位于第三代上海同步輻射裝置的BL14W1 是一個高性能的X射線吸收譜光束線站。在一期的七條光束線站中BL14W1設(shè)計為通用吸收譜線站。BL14W1 的光源是一個38

2、極Wiggler插入件，最大磁場為1.2T，磁場周期為80mm. XAFS光束線的主要光學(xué)部件包括一個準(zhǔn)直鏡，一個配有Si (111) 和 Si (311)的液氮冷卻雙晶單色器，一個聚焦鏡，一個高次諧波抑制鏡。光束線有聚焦和非聚焦兩種工作模式，其中，聚焦模式下能量范圍為422.5keV，非聚焦模式下的能量范圍為3.550keV。 同步裝置束線能量范圍keV分辨率E/E光通量10kevPhs/sAS（澳大利亞）XAFS4-40510-5210-410121013SPing-8（日本）BL01B13.8-113310-5310-41091011Diamond（英國）I-204-3410-4 10-

3、51012BSRF（北京）1W1B4-301310-421011SSRF（上海）BL14W1450510-5210-410121013國內(nèi)外同類線站性能比較國內(nèi)外同類線站性能比較010203040501011101210131014BSRF 1W1SSRF MPW Spectral flux (photons/s/0.1%bw)Photon energy (keV) New BSRF, 1W1: Ee=2.5GeV, Ie=250mA B0=1.28T, 14poles, 1.0 x 0.12mrad2 SSRF MPW: Ee=3.5GeV, Ie=300mA B0=1.2T, 38pole

4、s, 1.5 x 0.10mrad2Experimental StationPotential capabilityMinimum Detection Limit 1ppmIt is a general and high performance XAFS beamline, with high flux、high signal/noise ratio and fast data collection.XAFS analytical techniques at SSRF32元高純元高純Ge探測器及探測器及XIA電子學(xué)系統(tǒng)電子學(xué)系統(tǒng)4元元Si漂移探測器及采集系統(tǒng)漂移探測器及采集系統(tǒng)Lytle 熒光

5、電離室熒光電離室Oxford 電離室電離室五維樣品臺五維樣品臺掠入射平臺掠入射平臺 低溫樣品室低溫樣品室 (4K) 和高溫爐和高溫爐XAFS線站主要儀器設(shè)備線站主要儀器設(shè)備XAFS線站主要實驗技術(shù)線站主要實驗技術(shù)透射透射 XAFS （Transmission XAFS）熒光熒光 XAFS（Fluoresce XAFS）掠入射掠入射 XAFS （Grazing Incident XAFS） 原位原位 XAFS （In situ XAFS ）快速快速 XAFS (QXAFS) Conventional XAFS and QXAFS spectra (5 Sec) of Cu foil at K e

6、dge measured at BL14W1 beamline in comparison with standard XAFS spectra (the data is from Chicago University XAFS library, which was measured in APS 13ID) comparison with APS standard XAFS spectraSR-XAFS實驗框圖 汽車尾氣的污染物，CO、HC以及NOx等，嚴(yán)重威脅到人類的生活，對其治理受到全球范圍的重視。 世界上污染最為嚴(yán)重的二十個城市，出現(xiàn)頻率最高的就是中國的城市，占據(jù)60%。 大氣污染問題

7、與汽車尾氣排放具有很高的相關(guān)性。 引起的呼吸系統(tǒng)疾病(主要是慢性阻塞性肺病)在我國城市居民主要疾病死亡構(gòu)成中占12.6%，59%以上的司機(jī)患有不同程度的呼吸道疾病 國內(nèi)不斷提高汽車尾氣排放處理標(biāo)準(zhǔn)。 國內(nèi)在尾氣處理催化劑研究人員眾多。用XAFS手段研究催化材料的重生問題，研究其反應(yīng)前后的結(jié)構(gòu)變化，發(fā)現(xiàn)其在催化反應(yīng)前后所處晶格和配位環(huán)境差異，解釋了其能長期保持高活性的原因。 SPring-8Nature 418, 164 - 167 (11 July 2002) 為了提高催化劑的催化效率，科學(xué)家利用同步輻射裝置開展很多原位實時監(jiān)測反應(yīng)過程的研究。XAFS可以提供很重要的在金屬催化劑反應(yīng)過程中，與

8、局域結(jié)構(gòu)和電子環(huán)境有關(guān)的原位動力學(xué)信息，他的動力學(xué)行為可以在ms, us,以至于ps. fs內(nèi)研究。M. A. Newton et al., Nature Materials 2007, 6, 528-532; Angew. Chem Int. Ed. 2007, 45, 8629-8631Fig. 99: Normalised Pd K edge energy dispersive EXAFS spectra derived during a switch from a 5%NO/He feed to a 5%CO/He feed (both 75mlmin1 flow) at 673 K

9、over a 1wt%Pd/10ZCA sample. Each spectrum was acquired in ca. 250 msecs. For clarity only 1 spectrum/second is plotted. The red to yellow shading is indicative of the switch from the NO to CO feed.Fig. 100: Infrared spectra (averaged over 9 reversible NO/CO switches) taken at the same time as the EX

10、AFS spectra shown in Figure 99, collected with a 3 Hz spectral acquistion speed. The major gas phase and surface functionalities observed during the experiment are indicated. Again the shading of the flow of the graph indicates the change of reactive feedstock.國內(nèi)的研究國內(nèi)的研究汽車尾氣凈化裝置及催化劑汽車尾氣凈化裝置及催化劑0.00.

11、0.8(d)Pt-Pt shell in PtO2Pt/Fe-Ba/Al2O3-O-500Pt/Fe-Ba/Al2O3-O-300 Pt/Fe-Ba/Al2O3-RFT Amplitude /a.u.R /nmPt-PtPt-FePt-O 通過EXAFS研究助劑Fe的添加對催化劑Pt/Ba/Al2O3 中Pt物種微觀結(jié)構(gòu)的影響，這種微觀結(jié)構(gòu)的改變對催化劑組分間的作用和催化性能產(chǎn)生了顯著影響。Meng M et al.Applied Catalysis B: Environmental 78 (2008) 38 “Ethanol is one of the

12、most ideal reactants for fuel cells,” said Brookhaven chemist Radoslav Adzic. “Its easy to produce, renewable, nontoxic, relatively easy to transport, and it has a high energy density. A major hurdle to the commercial use of direct ethanol fuel cells is the molecules slow, inefficient oxidation, whi

13、ch breaks the compound into hydrogen ions and electrons that are needed to generate electricity. Specifically, scientists have been unable to find a catalyst capable of breaking the bonds between ethanols carbon atoms. But at Brookhaven, scientists have found a winner. Made of platinum and rhodium a

14、toms on carbon-supported tin dioxide nanoparticles, the research teams electrocatalyst is capable of breaking carbon bonds at room temperature and efficiently oxidizing ethanol into carbon dioxide as the main reaction product. Other catalysts, by comparison, produce acetalhyde and acetic acid as the

15、 main products, which make them unsuitable for power generation. 氫電池：儲存、運輸困氫電池：儲存、運輸困難難甲醇電池：甲醇電池：CO中間物質(zhì)中間物質(zhì)乙醇電池：氧化困難，乙醇電池：氧化困難， “The ability to split the carbon-carbon bond and generate CO2 at room temperature is a completely new feature of catalysis,” Adzic said. “There are no other catalysts that

16、can achieve this at practical potentials.”The main absorption peaks at the Rh and Pt edges have a very small potential dependence, indicating that the surfaces are only slightly oxidized, unlike the process that occurs with the pure Rh phase. It is likely that OH, which is present on the SnO2 surfac

17、e in aqueous solutions, causes a shift in surface oxidation of Rh and Pt (Rh or PtOH formation)Measurements of metal metal (RhPt and PtRh) coordination numbers NRh-Pt and NPt-Rhenabled us to obtain the average composition of the nanoparticles: x(Pt)/x(Rh) = NRh-Pt/NPt-Rh = 2.1(0.3), in reasonably go

18、od agreement with the ICP data x(Pt)/x(Rh)=1.5(0.2). The absolute values of these coordination numbers indicate the same size range (13 nm) as obtained by TEM. The obtained Pt and Rh coordination numbers have similar values 9.5(0.8) and 10.8(0.8) respectively, consistent with homogeneous distributio

19、n of Pt and Rh throughout the particles.In addition, as the NPtPt/NPtRh and NRhPt/NRhRh ratios were found to be consistent, with the bulk ratios of Pt and Rh concentrations obtained independently byEXAFS and ICP, we conclude that the Pt and Rh formed a quasi-random alloy. Further independent evidenc

20、e towards that conclusion is the similarity between the PtPt, PtRh and RhRh bond lengths found by our EXAFS analysis: 2.743, 2.725 , and 2.705 , respectively, that is, characterized by a much smaller spread than between pure Pt (2.775 ) and Rh (2.689 ).in situ IRRAS to identify the intermediates and

21、 products of ethanol oxidationXAS of Platinum Monolayer Fuel CellElectrocatalysts Unambiguous, Direct Correlationof Spectroscopy Data with Catalytic Properties(a) Models of pseudomorphic monolayers of Pt on three different substrates inducing compressive strain (Ru(0001) and Pd(111) and expansive st

22、rain (Au(111). (b) Schematic of Pt monolayer electrocatalyst subjectto synchrotron X-rayK. Sasaki, R. R. Adzic. Synchrotron Radiatin News, 2009, 22, 17-21Structural and Electronic Properties of Platinum Nanoparticle Surface in an Aqueous System Probed by In Situ X-ray Absorption Spectroscopy其他幾個與電池材

23、料有關(guān)的例子LixFePO4 cathode0.1 Hz, averaged over 75 spectra, lithiation speed C/3, starting with x=0.56.Oxidation state changes from Fe3+ to Fe2+.Fe K-edgeEdge shift at m md = 0.5LixNi0.5Mn0.5O2-cathodeMeasured at Ni K- and Mn K-edges alternately during discharge.0.1 Hz, averaged over 20 spectra. Lithiat

24、ion speed C/4.5, starting with x=0.414.Oxidation state changes from Ni4+ over Ni3+ to Ni2+.Ni K-edgeLixNi0.5Mn0.5O2-cathodeMeasured at Ni K- and Mn K-edges alternately during discharge.0.1 Hz, averaged over 20 spectra. Lithiation speed C/4.5, starting with x=0.414.Significant changes in the EXAFS.Ni

25、 K-edgeLixNi0.5Mn0.5O2-cathodeMeasured at Ni K- and Mn K-edges alternately during discharge.0.1 Hz, averaged over 20 spectra. Lithiation speed C/4.5, starting with x=0.414.Oxidation state of Mn stays in a tetravalent state.Mn K-edge直接甲醇燃料電池直接甲醇燃料電池DMFCElectrochemical cell for in situ EXAFS of fuel c

26、ell electrodes on station 16.5 at the SRS, DaresburyPEM fuel cell for in situ EXAFS studies of anode or cathode catalysts on station 16.5 at the SRS, Daresbury. The cell design enables the study of realistic catalyst loadings of 1 mg Pt per cm-2 of electrode area and operates under fully humidified

27、conditions at 80 C.優(yōu)點優(yōu)點缺點缺點QXAFS-催化催化-Pt/Al2O3-CO-氧化氧化The study of transient states of matter that last nanoseconds (10-9 s), or even picoseconds (10-12 s), is one of the scientific challenges that the ESRF has taken up successfully. For example, researchers observed what happens to the C2H4I2 molec

28、ule in water when hit by a flash of laser light. The pump and probe technique used in this experiment may also help in the future to study nanomaterials and proteins in action.H. Ihee et al., Science 2005, 309, 1223XAFSXAFS在多相催化中應(yīng)用在多相催化中應(yīng)用solid catalystgasesSurface eventsMolecular understandingAtomi

29、c scale constructionDynamic probe of operating state在在原子精度原子精度上設(shè)計、構(gòu)筑高效催化劑；在上設(shè)計、構(gòu)筑高效催化劑；在分子精度分子精度上揭示反應(yīng)物向產(chǎn)上揭示反應(yīng)物向產(chǎn)物的轉(zhuǎn)化；發(fā)展表征工具，物的轉(zhuǎn)化；發(fā)展表征工具，原位、實時、高空間分辨原位、實時、高空間分辨地表征地表征工作狀態(tài)工作狀態(tài)催化劑，實現(xiàn)對催化過程本質(zhì)的理解催化劑，實現(xiàn)對催化過程本質(zhì)的理解 DOE Report 2007Catalysis forms methanol from synthesis gas: CO + 2 H2 CH3OH.Also hydrogen can b

30、e produced from syngas via the water-gas-shift reaction: CO + H2O CO2 + H2.CuO/ZnO-catalyst, as prepared:Cu in solid solution with ZnO, substituting Zn2+ as Cu2+.Reduction of catalyst in H2 atmosphere: Cu reduced to metallic state, migrates to ZnO surface Cu forms particles of few nm size. Cluster s

31、ize and atomic structure is crucial for catalytic activity Smaller clusters larger specific surface higher activity less material needed (expensive, even noble metals!)Advancing Time-resolved Methods in Monitoringand Characterization of CatalystsReduction of a CuO/ZnO/Al2O3 methanol catalyst in H2 a

32、tmosphere, observed with 50 ms time resolution. Measurements performed at HASYLAB in collaboration with the group of B.S. Clausen.Goal: Faster (ms), wide spectral range, continuous movementCurrently up to 40 Hz possible 80 spectra / s 12.5 ms / spectrumMonochromatorCatalytic reactorCuOCuCu K-edgeD D

33、t=200 sJ.-D. Grunwaldt and A. Baiker, ETH ZrichCuOCuCu K-edgeD Dt=200 sCharacterization of multi component samples on mm-scale Valence distribution of elements2D-mapping:0.25 mm2 with 5 mm resolution: 10.000 spectra not feasible with conventional methods, 30 s/scan 3.5 days oscillating QEXAFS at mod

34、erate 10 Hz 8 min3D-Tomography:Even more time consumingFirst experiments at ESRF (BM) and APS (tapered undulator)Focussing with X-ray lenses Focal size 6 mm x 2 mm. Even dilute biological samples in fluorescence mode possible!horizontal focal size: 6-10 mCollaboration with RWTH Aachen (B. Lengeler)a

35、nd TU Dresden (C. Schroer)X-ray Absorption Spectroscopic Microscopy:From the Micro- to the NanoscaleXANES tomography: (a) schematic sketch of the sample.(b) Tomographic reconstruction of the sample on a virtual section at X-rayenergy E = 8995 eV. From the tomographic data set, the full XANES spectra

36、at each location on the virtual section can be reconstructed. Two examplespectra for locations shown in (b) are depicted in (c). (d) Relative concentrationsof metallic, monovalent, and bivalent Cu inside the glass capillary.The concentration of bivalent copper is below the detection limit of themeth

37、od. Attenuation generated by elements other than Cu is shown in thelower right image. acquire 10 spectra in 1 second sampling rate: 100 kHz 102 projections 91 points per projectionAt each position in the scan:Acquisition of tomographic data set:over 90.000 spectra with 104 points each 7 GByte of raw

38、 dataNear edge spectrum:Sample:CuO/ZnO catalyst in glass capillarySample in glass capillary, outer diameter 500 mm, inner diameter 400 mm.Beam size: 10 mm x 10 mmSample below / above Cu K-edgeReconstructed spectra with referencesC.G. Schroer et al., Appl. Phys. Lett. 82, 3360 (2003)Reconstruction at

39、 different positions after several oxidation/reduction cycles: What happens to the catalyst during catalysis?All spectra can be decomposed into content of the Cu-oxides and Cu to answer this question!Cu Cu(I) , 1.26 : 1 Average over whole cross section:Cu : Cu(I) = 51 : 49 Very detailed in situ obse

40、rvation of behaviour of real catalysts!XAFS在有機(jī)金屬化學(xué)中應(yīng)用在有機(jī)金屬化學(xué)中應(yīng)用-Zeolite-IrIron-platinum nanoparticles are known for their interesting magnetic properties. At the ESRF, they were subjected to successive treatments. The structural changes and their influence on the element-specific magnetic moments we

41、re monitored by the analysis of the X-ray absorption near-edge structure and the X-ray magnetic circular dichroism.The synthesised Fe50Pt50 particles were self-assembled on a silicon substrate and exposed to a soft hydrogen plasma. They were then annealed at 600C in order toachieve the chemically-or

42、dered L10 phaseC. Antoniak et al., Phys. Rev. Lett. 97, 117201 (2006).C 1s(C=C)* C=C：283.4 eVC 1s(C-H)* ring：285.2 eVC 1s(C-N) *ring：286.8 eV*CCJ. AM. CHEM. SOC. 9 VOL. 131, NO. 18, 2009中科院物理所中科院物理所 趙忠賢趙忠賢 丁洪丁洪 孫力玲孫力玲用于用于XAFS 實驗的金剛石實驗的金剛石5.705.725.745.765.785.800.00.51.01.52.02.5 Normalized intensit

43、y (a.u)Photon energy (keV) 1GPa 6.3GPa 9.6GPa 11.3GPa4f04f1048121620010203040500481216202030405060 CeFeAsO0.7F0.3 Pressure (GPa)Tc (K)(a)Tc (K) LaFeAsO0.5F0.5(b) SmFeAsO0.85CeFeAsO1-xFx鐵基超導(dǎo)材料結(jié)構(gòu)高壓與超導(dǎo)臨界溫度關(guān)系高壓X射線吸收譜（XAFS) 2008年春日本和中國科學(xué)家發(fā)現(xiàn)一種新型超導(dǎo)體年春日本和中國科學(xué)家發(fā)現(xiàn)一種新型超導(dǎo)體鐵基超鐵基超導(dǎo)材料。鐵基超導(dǎo)材料的發(fā)現(xiàn)為高溫超導(dǎo)研究和量子凝聚物導(dǎo)材料。鐵基超

44、導(dǎo)材料的發(fā)現(xiàn)為高溫超導(dǎo)研究和量子凝聚物理帶來了巨大的刺激和振奮，理帶來了巨大的刺激和振奮，XAFS將從原子和電子結(jié)構(gòu)上將從原子和電子結(jié)構(gòu)上理解高溫超導(dǎo)的深層機(jī)制理解高溫超導(dǎo)的深層機(jī)制 ，利用，利用SSRF高通量、高能量分辨高通量、高能量分辨的的XAFS光束線，獲得了高質(zhì)量高壓光束線，獲得了高質(zhì)量高壓XAFS譜。譜。 經(jīng)過輻照后，隨時間增加，伴隨主峰強(qiáng)度降低，吸收邊能量位移，和邊前峰的強(qiáng)度降低特征，判定三價鐵逐漸還原為二價鐵原位研究離子液體（原位研究離子液體（BmimFeCl4)的鐵的還原過程的鐵的還原過程 7120714071600.0 0min 20min 34min 49

45、min 64min 78min 98minIntensity of mainpeak decreaseIntensity of pre-edgepeak decrease Absorption coefficientEnergy (eV)Energy of absorptionedge shift中國科學(xué)院上海應(yīng)用物理研究所中國科學(xué)院上海應(yīng)用物理研究所此輻照反應(yīng)的機(jī)理為：Fe（）受X射線激發(fā)產(chǎn)生光電子或俄歇電子，隨后被Bmim+陽離子俘獲，成為溶劑化電子，此溶劑化電子繼而還原了Fe（），生成Fe（）；其次，F(xiàn)e（）被還原為Fe（）與Bmim+陽離子的分解是一個競爭過程，F(xiàn)e（）的被還原過程優(yōu)先于Bmim+陽離子的分解，在小范圍內(nèi)的Fe（）基本上反應(yīng)完全之后，Bmim+陽離子才開始分解。SnO2包裹的單分散超順磁包裹的單分散超順磁Fe的氧化物納米顆粒的氧化物納米顆粒的高溫穩(wěn)定性研究的高溫穩(wěn)定性研究 “ On the basis of XAFS results, it can be conclu