The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Characterisation of catalysts by TEM Di Wang Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, D-14195, Berlin, Germany

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Outline Complexity of heterogeneous catalysis Introduction to some important structures of heterogeneous catalysts TEM techniques in heterogeneous catalysis Characterisation of model catalysts

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Complexity of heterogeneous catalysis Heterogeneous catalysis Surface Science Solid State Physics/Chemistry Material synthesis Industry application Engineering

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Reactor operating Transport of mass and energy between catalyst particles Diffusion within catalyst particles Reaction cycles at active sites Elementary step reactions Space scaleTime scale myear mmms mm ss nmns pmPs, fs Decisively affect the course of heterogeneous catalytic reaction Complexity of heterogeneous catalysis

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Surface sensitive analytic methods: Raman and IR Raman: Identification of molecules AES: Surface element composition XPS: Element composition, bonding energy UPS: band structure Catalytic reaction takes place on the surface of heterogeneous catalyst Why TEM? Subsurface layers or bulk of catalyst may play important role in atom transportation or electron exchange Crystallographic information about active phase/active sites (usually in nanoscale) EELS — electronic structures High spatial resolution Complexity of heterogeneous catalysis Why TEM? Subsurface layers or bulk of catalyst may play important role in atom transportation or electron exchange Crystallographic information about active phase/active sites (usually in nanoscale) EELS — electronic structures High spatial resolution Mars van Krevelen mechanism O2O2 O H2OH2O O O2O2 Oxygen vacancy Bulk oxygen

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Important structures of heterogeneous catalysts Supported metalparticle size effects; metal-substrate interaction; structural change under chemical treatments Information of interests Transition metal oxidereduction behavior; defects structures Zeolites (porous structure)3D structure; intergrowth of different zeolitic structures; guest species inside a zeolitic host Carbon nanofibers as supportstructure and growing mechanisms

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Metals: fcc (close-packed), bcc and hexagonal (close-packed) Some alloys adopt the similar structure but reduce the symmetry by substituting some position by another type of atom, e.g., Pt 3 Si of primitive cubic structure. Important structures of heterogeneous catalysts Pt Si

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Size effect on metal particles (G. Rupprechter, H.-J. Freund, Top. Catal. 14 (2001) 3) Lattice contraction, e.g., Pt and Pd CO oxidation on Au/TiO 2 shows marked increase in reaction rate when the particles diameter is decreased below 3.5 nm down to 3.0 nm (M. Valden, etc., Science (1998)). Important structures of heterogeneous catalysts

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Metal oxides Rock-salt structure MO ReO 3 structure MO Rutile structure Important structures of heterogeneous catalysts

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – MoO 3 b c a b c a Important structures of heterogeneous catalysts

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Nonstoichiometry in transition metal oxides Crystallographic shear mechanism Mo n O 3n-2 (17  n  25) Mo 18 O 52,  derived from MoO 3 (layered structure) a b c 1/2 a M +1/2 c M 1/2 a M - 1/6 b M Important structures of heterogeneous catalysts

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – CS plane 1/2 a M +1/2 c M 1/2 a M - 1/6 b M Important structures of heterogeneous catalysts

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Mo n O 3n-1 (n<10) Mo 8 O 23, Mo 9 O 26,  derived from ReO 3 structure c a a (1 0 2) ReO3 c Mo 8 O 23 Mo 9 O 26 Important structures of heterogeneous catalysts

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – TEM techniques in heterogeneous catalysis Electron diffraction 1/ g L 22 D MoO 3 -[010] MoO 2 -polycrystalline

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Microdiffraction  22  < , Kossel-Möllenstedt condition Microdiffraction using small convergent angle from a Pt particle (about 10 nm in diameter) on [031] zone axis. 200 TEM techniques in heterogeneous catalysis

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – HRTEM In heterogeneous catalysts, structures of powders, thin film, small particle, as well as defect structures such as dislocation, planar defect, interface and cluster can be readily resolved. HRTEM image of CS structure formed during MoO 3 reduction under electron beam irradition TEM techniques in heterogeneous catalysis

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – The bright and dark spots in a HRTEM image usually CANNOT be directly interpretated as atom positions Very small particle leads to large reciprocal-space shape factor. “Reciprocal rod” may be intersected by the Ewald sphere even when the crystallite is not near a zone axis. Such excitation may introduce fringes not related to the structure of particle. g k k g TEM techniques in heterogeneous catalysis

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – EELS -zero-loss peak -plasmon peak -Inner-shell ionization edges, low intensity -Near edge structure on top of edges -background -Plural scattering Energy loss (eV) P L 2,3 B K C K N K V L 2,3 O K Amplified Zero loss Plasmon/Outer -shell electrons Background ELNES on appropriate ionisation edges of oxygen, carbon, metals, etc., can serve as “fingerprints” regarding changes in oxidation state, in chemical bonding and in the coordination environment of the detected species. TEM techniques in heterogeneous catalysis

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – EELS quantitative analysis  11 22 TEM techniques in heterogeneous catalysis

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Element mapping Pre-edge1 Pre-edge2 Post-edge TEM image of ZrN/ZrO 2 Oxygen map TEM techniques in heterogeneous catalysis

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction NaCl (001) plane Amorphous SiO 2 Pt Complex „real“ catalyst: randomly oriented and irregularly shaped metal particles on high surface area porous supports Model catalyst: well oriented and regularly shaped metal particles grown on planar thin supports Adventages: 1. facilitating TEM observation 2. serving as well-defined initial state and the structural change after the treatment (1 bar O 2, 673 K, 1h, then 1 bar H 2, 873 K, 1h) could easily be seen

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – As-grown sample Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Overview and SAED after the reduction Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – d values measured (Å) Pt 3 Si (cubic) d (Å) (hkl) Pt 3 Si (monoclinic) d (Å) (hkl) Pt 12 Si 5 (tetragonal) d (Å) (hkl) Pt d (Å) (hkl) (100) 2.75 (110) 1.94 (200) 1.37 (220) 1.17 (311) 3.88 (002) 2.78 (202) 2.69 (-202) 2.36 (113) 2.21 (-222) 1.80 (313) 1.50 (115) 1.39 (404) 3.48 (301) 3.01 (420) 2.76 (331) 2.36 (222) 2.13 (620) 1.82 (003) 1.96 (200) 1.39 (220) 1.18 (311) Measured interplanar spacings d (Å) compared with those of Pt 3 Si (cubic) Pt 3 Si (monoclinic), Pt 12 Si 5 and Pt. Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction HRTEM images of particles after the reduction Pt 3 Si with Cu 3 Au structuremonoclinic Pt 3 Si

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – HRTEM image of a particle after the reduction Pt 12 Si 5 particle on [276] zone axis Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – [100] Pt [100] Pt 3 Si Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction Microdiffraction from individual particle after the reduction

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – [152] Pt 12 Si 5 Microdiffraction from individual particle after the reduction Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – The beginning stages of a coalescence process of three particles with platelet shape. Rearrangement and the diffusion of atoms Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction The coalescence of two crystallites with an interface formed in between

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction The overlapping of different phases

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction ELNES of Si L edge taken from the free silica substrate and from areas with particles for as-grown sample and that after the reduction

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Structure characterisation Platinum silicides of cubic Pt 3 Si with Cu 3 Au structure, monoclinic Pt 3 Si and Pt 12 Si 5 are formed after reducing the Pt/SiO 2 system in H 2 at 873 K. Most platelet-shaped particles comprise Pt 3 Si while Pt 12 Si 5 is found in irregularly shaped particles. Other structural changes include the coalescence of neighbouring particles and the overlapping of different phases, etc. Mechanisms Dissociative adsorption of hydrogen on platinum particles Penetration of the metal-support interface by atomic hydrogen and the reduction of SiO 2 accompanied by the migration of Si atoms into the Pt particles leading to silicides formation Melting and recrystallisation must be taken into account in order to interpret the observed particles of lower Pt content and their morphology. Characterisation of model catalysts Pt/SiO 2 — a case of metal-support interaction

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – VPO catalysts — what is active phase? O 3.5 O 2 (g) (VO) 2 P 2 O 7 +4H 2 O O O Oxidation of n-butane to maleic anhydride C 4 H 10 C4H2O3C4H2O3 Sample preparation CAT1: V 2 O 4, H 2 O, H 3 PO 4 CAT2: V 2 O 4, H 2 O, H 4 P 2 O 7 Heating at 145 °C for 72 h Washed and dried in air at 120 °C for 16 h Precursor VOHPO 4  0.5H 2 O Activation in n-butane/air at 400 °C Catalyst Characterisation of model catalysts

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Characterisation of model catalysts CAT1 (VO) 2 P 2 O 7 on [100] zone axis (VO) 2 P 2 O 7 S.G.Pca2 1 a = Å b = Å c = Å VPO catalysts — what is active phase?

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Characterisation of model catalysts CAT1 VPO catalysts — what is active phase? Possible V 5+ phase at the surface of (VO) 2 P 2 O 7

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Characterisation of model catalysts CAT1 VPO catalysts — what is active phase? Amorphous region

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – CAT2 (VO) 2 P 2 O 7 on [100] zone axis Characterisation of model catalysts VPO catalysts — what is active phase?

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 –  II VOPO 4 on [001] zone axis  II VOPO 4 S.G.P4/n a = Å c = Å 110 Characterisation of model catalysts VPO catalysts — what is active phase? CAT2

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – V 5+ V 4+ Characterisation of model catalysts VPO catalysts — what is active phase? ELNES of V L-edge and O K-edge of reference VOPO 4 and the catalysts

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – (VO) 2 P 2 O 7 is the major phase in the activated catalysts. Other features, such as VOPO 4, disordered and amorphous regions in (VO) 2 P 2 O 7 crystallites, indicate the existence of V 5+ species. The interaction between V 4+ and V 5+ phases could be essential to the improvement of specific catalytic activities. But the role of V 5+ in VPO catalyst is not clear. Characterisation of model catalysts VPO catalysts — what is active phase?

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Summary SAED — crystal structure and phase constitution Microdiffraction — structure of small crystallite with size down to several nm HRTEM — local structural information of bulk, surface, defects, amorphous region and other features; The microstructural features are often important to catalytic reactivity. EELS and ELNES — element composition and distribution; valence state, especially oxidation state and coordination of the detected atoms. Importance of model catalyst — simplifying complex system; facilitating analytic techniques; aware of the gap between the TEM environment and the “real” condition. Distinguish electron induced effect from intrinsic features of catalyst

The 36 th Erice Crystallographic course on Electron Crystallography: Novel approaches for structure determination of nanosized materials, Erice, Italy, June 9 – Acknowledgement Fritz Haber Institute A. Liskowski Dr. D.S. Su Prof. R. Schlögl Leopold-Franzens University, Innsbruck, Austria S. Penner Prof. K. Hayek Cardiff University, UK Prof. G.J. Hatchings