Roger De Gryse

A heterogeneous Ru–hydroxyapatite catalyst for mild racemization of alcohols

Racemization of chirally stable secondary alcohols was performed using a truly heterogeneous catalyst under mild reaction conditions in the absence of any additive or cocatalyst. The catalyst is based on Ru3+ immobilized on calcium hydroxyapatite (Ru–HAP). The preparation of the calcium hydroxyapatite (HAP) support and the Ru content and immobilization were optimized leading to maximal catalytic performance. Via combined XRD, Raman, SEM, XPS, EPR, N2 adsorption, and ICP analysis, information on both the compositional and the structural properties of the material was obtained. The Ru–HAP catalyst is able to racemize benzylic as well as aliphatic secondary alcohols. The catalyst scope was further investigated for racemization of several mono- and polyfunctional secondary alcohols. Performing standard racemization of a reference substrate in the presence of a functional additive demonstrated the inhibitory effect of some of these functions. Finally the heterogeneous nature of the catalyst was verified by filtrate tests.

Yttria-stabilized zirconia thin films grown by reactive r.f. magnetron sputtering

Abstract Zirconia thin films were deposited on different substrates by reactive r.f. magnetron sputtering. It was found that zirconia layers grew preferentially in the (200) direction with a columnar microstructure that is independent of the oxygen flow, argon to oxygen flow ratios and sputtering pressure. On the other hand the substrate roughness clearly affects the orientation of zirconia. Distinct changes were observed in the case of heated substrates. The heating of the substrates does not change the form of the zirconia, but strongly influences its orientation. When the substrate temperature increases, the crystallographic orientation gets more and more random, typically for the polycrystalline state. A decrease in the optical transmittance and an increase in the colour intensity of the layers with an increase in the substrate temperature was also found. As is shown, the oxygen non-stoichiometry of the zirconia is responsible for these changes.

TiO2 films prepared by DC magnetron sputtering from ceramic targets

Abstract The deposition of stoichiometric TiO 2 films for V 2 O 5 /TiO 2 anatase catalysts was investigated. DC magnetron sputtering from ceramic oxide targets in an argon/oxygen atmosphere was chosen as deposition technique. The target behaviour upon sputtering was followed by means of the target voltage. The layers were prepared with different oxygen concentrations in the plasma and the influence upon electronic and optical properties of the deposited layers was investigated. Surface XPS measurements showed that stoichiometry is obtained for low oxygen mole fractions, while for higher oxygen contributions, Ti 3+ species are increasingly present. This departure from stoichiometry is ascribed to active resputtering of the deposited layer by O − ions. Due to the higher sputter yield of oxygen as compared to titanium, this resputtering resulted in the observed reduction. From optical transmission measurements, the refractive index was found to decrease with increasing oxygen mole fraction, while the band gap increased considerably. The variation of the optical absorption with the oxygen concentration in the plasma was found to confirm the XPS analysis regarding the stoichiometry of the layers. Polycrystalline anatase layers were obtained at elevated substrate temperatures.

A Mineral TiO2(001) Anatase Crystal Examined by XPS

X-ray photoelectron spectroscopy measurements with Al Kα radiation of the Ti 2p, Ti 3p, O 1s, and O 2s core levels of a mineral anatase TiO2(001) crystal are presented. The weak Ti 3p and O 2s photopeaks were measured with two resolutions. The valence band is also presented.

Crystallization of yttria under hydrothermal conditions

Abstract The effect of precursor type and hydrothermal crystallization conditions on the morphology of yttria grains was studied. Yttrium nitrate and yttrium chloride were used as yttrium salts soluble in water. Yttrium hydroxide obtained by the reaction of the chosen salt with ammonia was subjected to hydrothermal conditions (200–270 °C, 0–120 min) in an autoclave. The shape of the yttria grains was strongly dependent on the crystallization temperature and the type of precursor used. With yttrium chloride as a precursor and at crystallization temperatures up to 498K, yttria grains are isometric in shape. Above this temperature yttria grains get elongated with a needle-like shape. The size of the needles depends on the crystallization time. For the case of the yttrium nitrate precursor, the critical temperature of crystallization, above which extended yttria grains appear, is about 25 °C higher. From the results a model mechanism for the hydrothermal crystallization of yttria is proposed.

Effect of Substrate Sodium Content on Crystallization and Photocatalytic Activity of TiO2 Films Prepared by DC Magnetron Sputtering

The effect of sodium content of the glass support on the crystallinity of sputtered TiO2 films and photocatalytic breakdown of ethanol has been studied. It was found that the activity of the as-deposited (amorphous) films does not depend on the type of support used. The chemical composition of the glass support does influence the activity of annealed films. When using soda-lime glass support sodium diffuses into the film upon annealing, suppressing anatase crystallization and decreasing its photocatalytic activity. To decrease the influence of sodium, soda-lime glass coated with an e-beam evaporated SiO2 barrier layer was used with good result. A reduced sodium concentration in the film leads to well crystallized anatase after annealing. An increased photocatalytic activity was observed for these films.

Yttria-stabilized zirconia thin films grown by r.f. magnetron sputtering from an oxide target

Abstract Yttria-stabilized zirconia thin films with cubic crystallographic structure were deposited onto glass substrates by r.f. magnetron sputtering from an oxide target. It was found that zirconia growth is strongly dependent on the sputtering power and pressure. At low power and high pressure, zirconia grows preferentially in the (200) direction with columnar microstructurc. In contrast, high power and low sputtering pressures promote the growth of randomly oriented polycrystallinc zirconia. Increasing the argon flow at constant power and sputtering pressure again favours preferential growth of zirconia layers, however, not in the (200) direction as before, but in the (111) direction.

Silica-supported chromium oxide: colloids as building blocks.

In this contribution, the formation and immobilisation of chromium(iii) hydroxyoxide colloids is investigated. Nano-sized Cr(iii) colloids are generated in situ upon reduction of Cr(vi), dosed to a stirred reactor. The growth of the elementary colloids by the consumption of solved Cr is kinetically unfavorable compared to their aggregation to larger secondary particles, the size of which depends on the concentration of the building block colloids. This aggregation process can be steered by simple process parameters such as dosing rate and concentration of the Cr(vi). The Cr(iii) colloids are immobilised in situ on a support material via precipitation chromatography. Upon drying, the initially amorphose hydroxyoxides are gradually transformed into crystalline Cr(2)O(3) nanoparticles, mainly located at the external surface of the support. This approach opens new opportunities for the synthesis of supported metal oxide catalysts.

Biaxially Aligned Yttria Stabilized Zirconia and Titanium Nitride Layers Deposited by Unbalanced Magnetron Sputtering

Control of the texture and the biaxial alignment of sputter deposited films has provoked a great deal of interest due to its technological importance. Indeed, many physical properties of thin films are influenced by the biaxial alignment. In this context, extensive research has been established to understand the growth mechanism of biaxially aligned Yttria Stabilized Zirconia (YSZ) as a buffer layer for high temperature superconducting copper oxides. In this work, the growth mechanism in general and the mechanism responsible of the biaxial alignment in detail were investigated for thin films of YSZ and TiN deposited by unbalanced magnetron sputtering using non-aligned polycrystalline stainless steel substrates. The mechanism responsible for the preferential out-of-plane alignment has been investigated by performing depositions on a non-tilted substrate. However, to study the in-plane alignment a tilted substrate was used. The microstructure of the deposited layers was characterised by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The crystallographic alignment has been investigated by X-ray diffraction (XRD) (angular scans and pole figures) and by Selective Area Diffraction (SAD). It was observed that the deposited layers show a zone T or zone II structure and the layers with a zone T structure consist of faceted grains. There seems to be a correlation between the crystal habit of these faceted grains and the measured biaxial alignment. A model for the preferential out-ofplane orientation, the in-plane alignment and the correlation between the microstructure and the biaxial alignment is proposed.

Growth mechanism of biaxially aligned magnesium oxide deposited by unbalanced magnetron sputtering

For many years magnesium oxide (MgO) has been a topic of research as buffer layer for high-temperature superconducting copper oxides and as protective layer in plasma display panels. Since epitaxial growth of MgO is expensive, time consuming and size restricted, other techniques have been developed to grow highly oriented MgO layers for industrial processes. MgO thin films were deposited on a tilted polycrystalline substrate by reactive sputtering using an unbalanced magnetron. By varying different deposition parameters, it is possible to grow biaxially aligned MgO layers, i.e. layers with both out-of-plane and in-plane alignment. XRD measurements were performed to examine the crystallographic structure of the thin film. The preferential out-of-plane orientation is analysed by angular scans using the peak intensity of different reflections while the in-plane orientation is determined by (002) pole figures. Fully [111] out-of-plane oriented layers were grown with a strong in-plane alignment. SEM and TEM measurements were performed to reveal the topographical and cross-sectional microstructure and to investigate the texture evolution of the MgO layers. Evolutionary columnar growth and a roof-tile surface have been observed.