Extended abstract of a paper presented at MC 2007, 33rd DGE Conference in Saarbrücken, Germany, September 2 – September 7, 2007

Extended abstract of a paper presented at MC 2007, 33rd DGE Conference in Saarbrücken, Germany, September 2 – September 7, 2007

Extended abstract of a paper presented at MC 2007, 33rd DGE Conference in Saarbrücken, Germany, September 2 – September 7, 2007

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005

The application of modern transmission electron microscopes (TEM) in catalytic research has accelerated the progress in understanding the mechanism of catalytic reactions. For instance, using environmental TEM, the novel glide shear defect process was revealed as an efficient mechanism for the release of the structural oxygen of vanadyl pyrophosphate in the n-butane oxidation [1]. On the other hand, electron energy-loss spectroscopy (EELS), which is nowadays commercially available on modern TEM, appears unknown in the catalytic community. in fact, core-loss EELS is a powerful tool to identify the chemical state of elements and to study the modification of this sate in various compounds.

Fig.l shows EELS-spectra of various vanadium oxides in which the oxidation state of vanadium varies from 2+ (VO) to 5+ (V2O5). The first two features, marked as V L3 and V L2 edges, are attributed to the excitations from V 2p3/2and V 2p1/2core levels to the unoccupied V 3dstates, respectively.

Many catalytic materials, especially the maximum valence transition metal oxides, are particularly susceptible to electron beam irradiation and thus undergo structural changes. Hence knowledge about the behaviour of catalytic materials under the electron beam is of importance for all TEM investigations of such materials. On the other hand, this effect can be utilised for an in-situ study of the reductive property, phase transition and/or phase stability of various transition metal oxides in an inert, simple ambient high-vacuum. The knowledge so obtained is needed for understanding the reduction mechanism of catalysts in more complicated chemical environments. in the present work, we study the electron beam induced change in MoO3 and TiO2 (anatase) by means of electron energy-loss spectroscopy (EELS), electron diffraction and high-resolution electron microscopy (HREM).

Molybdenum trioxide, MoO3, important as catalyst in the selective oxidation of hydrocarbons, forms an orthorhombic crystal layer structure. Fig. 1 shows oxygen AT-edges recorded at various irradiation periods in a Philips 200 FEG electron microscope.

An instrument equipped with total electron yield detectors was designed and constructed for in situ X-ray absorption spectroscopy (XAS) investigations in the soft X-ray range (100 eV ≤ hν ≤ 1000 eV) at elevated pressures (mbar range) and sample temperatures (T ≤ 1000 K) [1]. This allows, for the first time, XAS studies in a surface-sensitive mode of the light elements (Z = 3-15). Furthermore, the gas phase XAS and the surface-related XAS of the solid state phase can be collected simultaneously in order to correlate the gas/solid reaction rate with the surface electronic structure under working conditions in a flow-through mode.

The novel experimental tool represents a contribution to the experimental overcoming of the “pressure gap” in material science. In this work examples are presented belonging to the field of heterogeneous catalysis [2-4] and to the reactivity of diamond surfaces [5]. Additionally, prospects for in situ studies in material science will be given.

Oxidic zirconium films prepared by chemical deposition from aqueous medium on sulfonic acid terminated self-assembled monolayers attached to an oxidized silicon surface were investigated with scanning electron microscopy and atomic force microscopy. Bulk precipitate forms in the 4 mM Zr(SO4)2 · 4H2O, 0.4 N HCl deposition medium at 343 K after approximately 30 min. Precipitate particles (200 nm and larger) were found embedded in the oxidic zirconium film and adsorbed on top of the film; they could be washed off, but patches of the film were removed. Working with unstable deposition solutions, in which homogeneous nucleation occurs, leads to preparation-inherent flaws in the film.

The surface morphology of TiO2- and ZrO2-based thin films, deposited from aqueous solution at 70–80 °C onto functionalized organic self-assembled monolayers (SAMs) on silicon has been examined using atomic force microscopy (AFM). The films have been previously shown to consist, respectively, of nanocrystalline TiO2 (anatase) and of nanocrystalline tetragonal ZrO2 with amorphous basic zirconium sulfate. The films exhibit characteristic surface roughnesses on two length scales. Roughness on the nanometer scale appears to be dictated by the size of the crystallites in the film. Roughness on the micron scale is postulated to be related to several factors, including the topography of the SAM and the effects of larger, physisorbed particles or agglomerates. The topographies of the oxide thin films, on both the nanometer and micron scales, are consistent with a particle-attachment mechanism of film growth.

The superconducting properties of several binary and ternary fullerene compounds are investigated by means of ac susceptibility technique. The susceptibility X = X'-iX” is observed as a function of temperature for different magnetic field amplitudes (0.01 G - 20 G). The samples are characterized by X-ray diffraction (XRD) analysis and the fcc-lattice constants a0 are determined. Furthermore the influence of the preparation procedure, especially the treatment of the C60 starting material on the superconducting properties is discussed.

Prompted by earlier work showing that graphite intercalation compounds form superconducting ternary compounds in which thallium plays an important role C60 has been doped with Tl-alloys. Results of dc-magnetization, ac-susceptibility, X-ray analysis and NMR investigations will be presented.

The importance of a number of techniques (including 1H and 13C NMR, XRD and IR) in exploring the important catalytic properties of synthetic and natural clays is described. A clear distinction is observed between proven catalytically-active clays (e.g. Al-exchanged) and those which are generally less effective (e.g. Na-exchanged). 13C NMR spectroscopy is used to identify directly products formed within the interlayer regions, and temperature-controlled powder XRD serves as a useful tool for identifying whether or not intercalation occurs under variously defined conditions. High-pressure XRD is used to verify the formation of different products during reaction.