Synchrotron radiation and catalysis. A. Martorana - X School on Synchrotron Radiation - Duino, September 16th 2009

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1 Synchrotron radiation and catalysis A. Martorana - X School on Synchrotron Radiation - Duino, September 16th

2 What is a catalyst Why synchrotron light is suitable in catalysis Some details of instrumentation Some applications A. Martorana - X School on Synchrotron Radiation - Duino, September 16th

3 Catalyst: A substance that modifies the rate of a chemical reaction but does not undergo any permanent chemical modification: the chemical equilibrium R P is not modified A catalyst provides a reaction path with lesser activation energy with respect to an uncatalyzed reaction k = A e (-E a /RT) A. Martorana - X School on Synchrotron Radiation - Duino, September 16th

4 Homogeneous catalysts: share the same state as the reacting substances (often all are in solution) Heterogeneous catalysts: are in a different state, typically solid catalyst and gaseous reactants e.g. a metal nanophase supported on an oxide (Pt/CZ, Pd/silica, Pt/alumina, etc.) A. Martorana - X School on Synchrotron Radiation - Duino, September 16th

5 H 2 2H + +2e - 1/2O 2 +2e - O 2- H 2 +1/2O 2 H 2 O 5

6 Oxidation of carbon monoxide: 2CO+O 2 2CO 2 Reaction mechanism and reaction path on a 13 atoms Au cluster: Prestianni, Martorana, Ciofini, Labat, Adamo, J.Phys.Chem. C 112 (2008)

7 Single site mechanism 1, Au

8 Is it possible (today) to visualize a chemical reaction by synchrotron techniques? Plech, Wulff et al., Phys. Rev. Lett. 92 (2004)

The blue bars show the positions of the first two intermolecular peaks in the partial distribution

9 FIG. 5 (color). The change in the atom-atom pair distribution ΔS(r,τ); for 200 ps, 1 ns, and 1 s. The green bars indicate the bond lengths of iodine in the X and the A=A0 state. The blue bars show the positions of the first two intermolecular peaks in the partial distribution function gcl-cl. These Cl atoms are located in the first solvation shell of CCl4 Plech, Wulff et al., Phys. Rev. Lett. 92 (2004)

10 Is it possible (today) to visualize a chemical reaction by synchrotron techniques? Hardly, for simple and slow chemical reactions Then, what can we do with synchrotron techniques applied to catalysis studies? A. Martorana - X School on Synchrotron Radiation - Duino, September 16th

11 Structural characterization of gold nanoclusters Supported on silica for: - analysis of dispersion - analysis of the atomic structure A. Martorana - X School on Synchrotron Radiation - Duino, September 16th

12 Atomic arrangements of fcc metal clusters truncated octahedron and cuboctahedron icosahedra (two sizes) truncated decahedron (side and top view) fig 5 decaedro di Marks (da due angoli visuali diversi) e decaedro non troncato 12

13 The Debye equation tm I( q ) = f 2 µ(t m )sin(2π q t m )/(2π q t m ) q =(2sinθ)/λ length of the scattering vector t m µ(t m ) vector distance between a couple of atoms multiplicity of t m in the nanocrystal 13

The Debye equation for stacking faults I pqm = µ(t pqm ) p (0) m sin( q t pqm )/( q t pqm ) + 1 3 p m (+) 3 sin( q t pqm + t (+) i )/( q t pqm + t

14 The Debye equation for stacking faults I pqm = µ(t pqm ) p (0) m sin( q t pqm )/( q t pqm ) p m (+) 3 sin( q t pqm + t (+) i )/( q t pqm + t (+) i ) + i=1 1 3 p m ( ) 3 sin( q t pqm + t ( ) i )/( q t pqm + t ( ) i ) i=1 I = t pqm I pqm 14 Longo & Martorana, J. Appl. Cryst. 41 (2008) 446

15 Fitting with SF, microstrains and lognormal size distribution Longo & Martorana, J. Appl. Cryst. 41 (2008)

16 Fitting with icosahedral, decahedral and fcc,lognormal distributed particles 16

17 EXAFS RDF simulation with the components (fcc, deca, ico) of XRD fit Longo & Martorana, J. Appl. Cryst. 41 (2008)

18 Carbon Monoxide over Pt/Al2O3 : What is the active Pt oxidation state? 18

19 Singh et al. Angew. Chemie Int. Ed. 47 (2008) 9260 Generating Highly Active Partially Oxidized Platinum during Oxidation of Carbon Monoxide over Pt/Al2O3 : In Situ, Time-Resolved, and High-Energy-Resolution X-Ray Absorption Spectroscopy 19

20 Figure 2. Pt L3 edge HERFD XANES of 2 wt% Pt/Al2O3 during oxidation of carbon monoxide at an oxygen/ carbon monoxide ratio of 1:1 a) measured during heating at 308 K (red), 328 K (green), 361 K (blue) 394 K (cyan), 425 K (pink), 443 K (orange), 475 K (yellow), and 491 K (gray) and b) during cooling at 503 K (black), 487 K (gray), 471 K (yellow), 453 K (orange), 421 K (pink), 387 K (cyan), 359 K (blue), 331 K (green), and 313 K (red). The ignition and extinction temperatures were 472 and 456 K, respectively. The arrows indicate the trends. Singh et al. Angew. Chemie Int. Ed. 47 (2008)

21 Figure 1. Pt L3 edge of 5 wt % Pt/Al2O3 after reduction in the presence of different atmospheres: He (black), He(O2) (red), and 1% CO/He (green) measured using total fluorescence detection (a) and HERFD XAS spectroscopy (b) Sofonova et al., J. Phys. Chem. B 110 (2006)

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23 Dispersion, aging, oxidation state, interaction with the support of Pt/Al2O3 and Pt/CZY 23

24 J. Sutter, SMEXOS conference, ESRF, Grenoble, February

25 J. Sutter, SMEXOS conference ESRF, Grenoble, February

26 Nagai et al. Angew. Chemie Int. Ed. 47 (2008) 9303 In Situ Redispersion of Platinum Autoexhaust Catalysts: An On-Line Approach to Increasing Catalyst Lifetimes? 26

27 Nagai et al. Angew. Chemie Int. Ed. 47 (2008)

28 Figure 1. Temporal dependence of the white-line peak height of the Pt LIII edge in XANES for fresh a) Pt/Al2O3 and b) Pt/CZY catalysts under oxidizing/reducing atmospheres at C and a schematic representation of the sintering/redispersion behavior. 1) 4% O2/He and 3% H2/He gases, 2) 20% O2/He and 3% H2/He gases were alternately introduced into the cell every 60 s throughout the measurement. Inset: Magnified view of initial stage of the experiment. 28

29 Nagai et al. Angew. Chemie Int. Ed. 47 (2008)

30 A not thoroughly inert support: in situ, time-resolved structural analysis of ceria/zirconia 30

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34 Deganello et al. J.Phys.Chem.B 110 (2006)

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39 Deganello et al. J.Phys.Chem.B 110 (2006)

40 Summary (and conclusions) - by synchrotron techniques it is hardly possible to visualize a chemical reaction (and in particular a chemical reaction on a catalytic site) However we can: - Finely characterize as prepared catalytic materials - perform time-resolved in operando studies: - carry out structural characterization - determine the oxidation state of the active species - analyze the interaction of the active species with a (more or less) inert support - get evidence about the really active phase - get knowledge for the design improved materials - 40

X-ray absorption spectroscopy

X-ray absorption spectroscopy Jagdeep Singh Jeroen A. van Bokhoven Absorption as function of energy of the x-ray Data-analysis Absorption (a.u.) 2.0 Pre-edge subtraction 1.5 1.0 0.5 0.0-0.5 8800 9000 9200