2 Structure Characterization

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Structure X-Ray Diffraction (XRD) Crystalline materials (long range order)

Principle of X-Ray Diffraction

Neutron scattering H/D containing molecules

X-Ray absorption spectroscopy (XAS) Amorphous materials ( p (short range order) g ) Composite materials

d

Interference of photons scattered by ordered structures Point lattice with crystalline long range (min. 10 unit cells) Interference positive for:

n = 2d sinBraggs Law

Long range order

X-Ray Powder Diffraction

Experimental Setup XRDPowder Diffraction

a. a

b. b

200 220 222 400 420 422 440 600 442 620 622 444 640 642

111 200 220 311 222 400 331 420 422 511 333 440 531 600 442 620 533 622 444 711 551 640

A fraction of the crystallites will be orientated to satisfy the Bragg condition for each set of planes (hkl). These (hkl) crystallites will be randomly oriented around the incoming beam, so the diffracted beams forms a cone around the incident beam at the angle of 2.

KCl

NaCl

Position of XRD linesPowder XRD of -Quarz

XRD: Identification of structureMiller indices

Neighboring atoms/ Free valences 12/0

8/4

7/5

9/3

Features of a powder XRD and their origin

Application of X-ray diffractionIn situ characterization of catalysts

M O reference MnO f Reduced Fe-MnO catalyst After CO hydrogenationFe (bcc) converts into Fe-carbides

60 min 40 min 20 min

Formation of Pd hydride during Benzene hydrogenation

Formation of metal oxide phasesin situ XRD

Properties of neutronsMass m=1.675 x 10-24g Charge = 0 Spin = Magnetic moment = 1.913 nuclear magnetons

Neutron wavelength range: 0.2 - 20 , 1 meV=8.065 cm-1

=k=

h 2 = mv k 2

Wave vector (mag.)

=

mv

Neutron energy

E=

2 2 1 2 k mv = 2 2m

Neutron momentum

p = mv = k

Reduction of a supported Cu catalysts

Interaction of neutrons with matterMomentum Transfer

Incoherent and coherent scattering cross-sections

p = mv = k Q=Q

(k

0

kf

)k0

Energy Transfer

E=

2 2 1 2 k mv = 2 2m2

D

= E0 E f =k= 2 = mv

2m

(k

2 0

k2 f

)

Incoherent scattering cross-section Coherent scattering cross-section Absorption cross-section

N

Ni

H

Coherent scattering interference effects between waves scattered from different nuclei Inelastic scattering kf < k0 (energy loss) Structure and motion of atoms relative to each other

Elastic scattering kf = k 0 0 =0 only momentum (Q) is transferred

Incoherent scattering deviation of individual atom positions from the g p mean potential Motion of single atoms

Elastic neutron scattering Elastic Neutron scattering is a coherent scattering process analogous to X-ray diffraction. kf = k0 only momentum is transferred ( y (no energy analysis) Incoherent scattering increases background use deuterated substances

Experimental setupElastic neutron scattering

Neutrons are scattered by the nuclei, Xrays b th electrons by the l t Light nuclei (e.g., H, C) are easier to locate in structures with heavy atoms by neutron diffractionNeutron scattering densities for C6D6 adsorbed on ZSM5, (top) 4 mol/UC, (bottom) 8 mol/UC

Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II)

Secondary Sources FRM-II

=243 mm, l=700 mm

http://www.frm2.tum.de

Thermal neutrons: from D2O moderator Hot source: Block of graphite (20 cm diameter, 30 cm high) heated by the gamma radiation to a temperature of ~ 2900 K. Spectrum from 100 meV to 1eV Cold source: Liquid D2 moderator (20 l) temperature about 25 K at a distance of 40 cm from the core axis. The cold neutron spectrum peaked around 5 meV

Neutron energies at the FRM-II

Spallation source ISIS

Energy of neutrons and their application in a research reactor. reactor The size of the colorized area is proportional to the amount of neutrons available for the application.

X-Ray absorption spectroscopy

X-Ray absorption edge

Absorption of X-ray's and promotion of a corelevel electron to continuum

X-Ray absorption near edge structure XANES

X-Ray absorption near edge structure Density of states (DOS)TiO2 Fe2O3

Extended X-ray absorption fine structure EXAFS

EXAFSSingle scattering plane wave approximation (k ) = 2 2 F (k ) N sin (2kr + (k )) e 2 k r2 k

0.4Constructive (in phase)

0.3 |FFT| 0.2 0.1 0.0 0 2 4 r[]

Due to (k) the distances are shifted to smaller values !!!

outgoing electron wave backscattered electron waveDestructive (out of phase)

6

8

10

Short range order

Cluster size and scattering contributions

Location of Zn2+ cations in zeolitesCoordination sites f Zn2 C for 2+ in zeolite Beta

0.08

0.06

NiO experimental i t NiO experimentall NiO 1 shell NiO 2 shells NiO 3 shells NiO 7 shells

2.1 2.1 2.0 3.4 2. 3 2.0 2.5 2.3 3.0

6-membered rings 5-membered rings2.3

FT mag. FT mag g.

0.04 0.04

4-membered rings

2.00.02 0 02 0.02

2.0 2.00 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8

0.00 0.00

r[A]

3.4 34

Preferential location of Zn2+ in BEASample Zn- BEAZn-BEA Z BEA

Bimetallic Ni-Rh catalysts (Ni-K edge)r 1.96 3.00FFT NiO

N 4.28 1.75 4 2 3 2 2 2

FFT mag

Zn 6MRZnO

1.97 3.43 2.30 2.77 1.98 2.05

Ni/HTC NiRh/HTC

Zn 5MR

Bimetallic catalyst 25% Ni, 0.89 wt% Rh

Metall 0 2 4 6 8

Zn 4MR

Ni foil

0

1

2

3 R ()

4

5

6

r []

Coordination parameters for Ni containing samplessample Ni-O N Ni foil NiO Ni/HTC NiRh/HTC 6 1.3 1.3 R () 2.07 2.05 2.05 2(2) N 12 12 9.4 9.2 Ni-Ni R () 2.49 2.94 2.49 2.48 2(2)

Preferential l P f ti l location of ti f

Zn2+ Z

at 6-MR positions t 6 MR iti

0.0081 0.0095

0.0043 0.0050

Bimetallic Ni-Rh catalysts (Rh-K edge)Rh2O3

X-Ray absorption near edge structureElectronic properties of d-metalsFermi level

Rh/HTC

Bimetallic catalyst 25% Ni, 0.89 wt% Rh

5d 5/2 Electron deficient Pt particlesNi Rh

5d

3/2

FFT

NiRh/HTC

Rh foil

2p2 3R ()

3/2

0

1

4

5

6

LIII2(2) N Rh-Ni R () 2(2)

Coordination parameters for Rh containing samplesSample N Rh foil Rh2O3 Rh/HTC NiRh/HTC 6 5.3 2.9 Rh-O R () 2.06 2.11 2.05 2(2) N 12 2.5 0.1 Rh-Rh R () 2.68 2.68 2.61

2p

1/2

L

II

Electron deficient particles show a higher peak above the absorption edge0.0017 0.0090 7.1 2.52 0.0041

0.0087 0.0029

Determination of oxidation state by XANES

Characterization of S-species (XANES S K-edge)

XANES for ZnS, ZnSO3 and ZnSO4

Comparison EXAFS and XANES EXAFS Single scattering dominates Mathematical description using phase shifts and amplitudes form experiment or theory

Experimental setup XASSample Cell Reference Slits Ionization Chambers SynchrotronMonochromator

Information level Structural environment Number and kind of Neighbors Distance Disorder Oxidation state Electronic information DOS in the final state Geometry, distortions

XANES Electronic transitions Multiple scattering Exact description based on quantum-mechanical calculations t h i l l l ti Interpretation of characteristic spectral features using references (peak fitting, PCA correlation fitting PCA, spectroscopy)

2 GeV 20 mA Pulslnge: 0.17 ns Pulsbastand 20 ns Radius 15.3m

The first accelerators (cyclotrons) were built by particle physicists in the 1930s. The nucleus of the atom was split using the collision of high energy particles. From the results of these collisions the physicists tried to deduce the laws of fundamental physics that govern our world and the whole of the universe. Synchrotron radiation was seen for the first time at the General Electric in the USA in 1947 in a different type of accelerator (synchrotron). It was first considered a nuisance because it caused the particles to lose energy, but in the 1960s exceptional properties as light source were recognized.

600 MeV 20 ma Radius 5 m

SRs Daresbry UK

10-15 MeV 20 mA

European Synchrotron Radiation FacilitiesESRF DESY

Development of available X-ray flux

Generation of X-Ray radiation

Design of in situ XAS cellsPlug flow reactor

Bending Magnet

Wiggler

CSTR type reactors (Continuous stirred tank reactor)Undulator U d l t

Sample cooling

Sample heating

Gas inlet

Free electron laser

Capton windows

Gas outlet