XAFS应用介绍

1、X射线吸收精细结构谱XAFS（实验方法和应用）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辐射装置的BL14W1 是一个高性能的X射线吸收谱光束线站。在一期的七条光束线站中BL14W1设计为通用吸收谱线站。BL14W1 的光源是一个38

2、极Wiggler插入件，最大磁场为1.2T，磁场周期为80mm. XAFS光束线的主要光学部件包括一个准直镜，一个配有Si (111) 和 Si (311)的液氮冷却双晶单色器，一个聚焦镜，一个高次谐波抑制镜。光束线有聚焦和非聚焦两种工作模式，其中，聚焦模式下能量范围为422.5keV，非聚焦模式下的能量范围为3.550keV。 同步装置束线能量范围keV分辨率E/E光通量10kevPhs/sAS（澳大利亚）XAFS4-40510-5210-410121013SPing-8（日本）BL01B13.8-113310-5310-41091011Diamond（英国）I-204-3410-4 10-

3、51012BSRF（北京）1W1B4-301310-421011SSRF（上海）BL14W1450510-5210-410121013国内外同类线站性能比较国内外同类线站性能比较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元高纯元高纯Ge探测器及探测器及XIA电子学系统电子学系统4元元Si漂移探测器及采集系统漂移探测器及采集系统Lytle 荧光

5、电离室荧光电离室Oxford 电离室电离室五维样品台五维样品台掠入射平台掠入射平台 低温样品室低温样品室 (4K) 和高温炉和高温炉XAFS线站主要仪器设备线站主要仪器设备XAFS线站主要实验技术线站主要实验技术透射透射 XAFS （Transmission XAFS）荧光荧光 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实验框图 汽车尾气的污染物，CO、HC以及NOx等，严重威胁到人类的生活，对其治理受到全球范围的重视。 世界上污染最为严重的二十个城市，出现频率最高的就是中国的城市，占据60%。 大气污染问题

7、与汽车尾气排放具有很高的相关性。 引起的呼吸系统疾病(主要是慢性阻塞性肺病)在我国城市居民主要疾病死亡构成中占12.6%，59%以上的司机患有不同程度的呼吸道疾病 国内不断提高汽车尾气排放处理标准。 国内在尾气处理催化剂研究人员众多。用XAFS手段研究催化材料的重生问题，研究其反应前后的结构变化，发现其在催化反应前后所处晶格和配位环境差异，解释了其能长期保持高活性的原因。 SPring-8Nature 418, 164 - 167 (11 July 2002) 为了提高催化剂的催化效率，科学家利用同步辐射装置开展很多原位实时监测反应过程的研究。XAFS可以提供很重要的在金属催化剂反应过程中，与

8、局域结构和电子环境有关的原位动力学信息，他的动力学行为可以在ms, us,以至于ps. fs内研究。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.国内的研究国内的研究汽车尾气净化装置及催化剂汽车尾气净化装置及催化剂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 通过EXAFS研究助剂Fe的添加对催化剂Pt/Ba/Al2O3 中Pt物种微观结构的影响，这种微观结构的改变对催化剂组分间的作用和催化性能产生了显著影响。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. 氢电池：储存、运输困氢电池：储存、运输困难难甲醇电池：甲醇电池：CO中间物质中间物质乙醇电池：氧化困难，乙醇电池：氧化困难， “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其他几个与电池材

23、料有关的例子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直接甲醇燃料电池直接甲醇燃料电池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.优点优点缺点缺点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在多相催化中应用在多相催化中应用solid catalystgasesSurface eventsMolecular understandingAtomi

29、c scale constructionDynamic probe of operating state在在原子精度原子精度上设计、构筑高效催化剂；在上设计、构筑高效催化剂；在分子精度分子精度上揭示反应物向产上揭示反应物向产物的转化；发展表征工具，物的转化；发展表征工具，原位、实时、高空间分辨原位、实时、高空间分辨地表征地表征工作状态工作状态催化剂，实现对催化过程本质的理解催化剂，实现对催化过程本质的理解 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在有机金属化学中应用在有机金属化学中应用-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 赵忠贤赵忠贤 丁洪丁洪 孙力玲孙力玲用于用于XAFS 实验的金刚石实验的金刚石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铁基超导材料结构高压与超导临界温度关系高压X射线吸收谱（XAFS) 2008年春日本和中国科学家发现一种新型超导体年春日本和中国科学家发现一种新型超导体铁基超铁基超导材料。铁基超导材料的发现为高温超导研究和量子凝聚物导材料。铁基超

44、导材料的发现为高温超导研究和量子凝聚物理带来了巨大的刺激和振奋，理带来了巨大的刺激和振奋，XAFS将从原子和电子结构上将从原子和电子结构上理解高温超导的深层机制理解高温超导的深层机制 ，利用，利用SSRF高通量、高能量分辨高通量、高能量分辨的的XAFS光束线，获得了高质量高压光束线，获得了高质量高压XAFS谱。谱。 经过辐照后，随时间增加，伴随主峰强度降低，吸收边能量位移，和边前峰的强度降低特征，判定三价铁逐渐还原为二价铁原位研究离子液体（原位研究离子液体（BmimFeCl4)的铁的还原过程的铁的还原过程 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中国科学院上海应用物理研究所中国科学院上海应用物理研究所此辐照反应的机理为：Fe（）受X射线激发产生光电子或俄歇电子，随后被Bmim+阳离子俘获，成为溶剂化电子，此溶剂化电子继而还原了Fe（），生成Fe（）；其次，Fe（）被还原为Fe（）与Bmim+阳离子的分解是一个竞争过程，Fe（）的被还原过程优先于Bmim+阳离子的分解，在小范围内的Fe（）基本上反应完全之后，Bmim+阳离子才开始分解。SnO2包裹的单分散超顺磁包裹的单分散超顺磁Fe的氧化物纳米颗粒的氧化物纳米颗粒的高温稳定性研究的高温稳定性研究 “ On the basis of XAFS results, it can be conclu