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Van Tendeloo L.,Center for Surface Chemistry and Catalysis | Gobechiya E.,Center for Surface Chemistry and Catalysis | Breynaert E.,Center for Surface Chemistry and Catalysis | Martens J.A.,Center for Surface Chemistry and Catalysis | Kirschhock C.E.A.,Center for Surface Chemistry and Catalysis
Chemical Communications | Year: 2013

Exposure of faujasite zeolites to different alkali hydroxide solutions readily yields zeolites with ABW, CHA, MER and ANA topologies. In NaOH faujasite persisted. Aside from new opportunities for zeolite synthesis, this reveals that a suitable aluminosilicate connectivity in the source material significantly facilitates zeolite crystallization. © 2013 The Royal Society of Chemistry.


Tsai M.-L.,Stanford University | Hadt R.G.,Stanford University | Vanelderen P.,Center for Surface Chemistry and Catalysis | Sels B.F.,Center for Surface Chemistry and Catalysis | And 2 more authors.
Journal of the American Chemical Society | Year: 2014

Understanding the formation mechanism of the [Cu2O]2+ active site in Cu-ZSM-5 is important for the design of efficient catalysts to selectively convert methane to methanol and related value-added chemicals and for N2O decomposition. Spectroscopically validated DFT calculations are used here to evaluate the thermodynamic and kinetic requirements for formation of [Cu2O]2+ active sites from the reaction between binuclear CuI sites and N2O in the 10-membered rings Cu-ZSM-5. Thermodynamically, the most stable CuI center prefers bidentate coordination with a close to linear bite angle. This binuclear CuI site reacts with N2O to generate the experimentally observed [Cu2O]2+ site. Kinetically, the reaction coordinate was evaluated for two representative binuclear CuI sites. When the Cu-Cu distance is sufficiently short (<4.2 Å), N2O can bind in a "bridged" μ-1,1-O fashion and the oxo-transfer reaction is calculated to proceed with a low activation energy barrier (2 kcal/mol). This is in good agreement with the experimental Ea for N2O activation (2.5 ± 0.5 kcal/mol). However, when the Cu-Cu distance is long (>5.0 Å), N2O binds in a "terminal" η1-O fashion to a single CuI site of the dimer and the resulting Ea for N2O activation is significantly higher (16 kcal/mol). Therefore, bridging N2O between two CuI centers is necessary for its efficient two-electron activation in [Cu2O]2+ active site formation. In nature, this N2O reduction reaction is catalyzed by a tetranuclear Cu Z cluster that has a higher Ea. The lower Ea for Cu-ZSM-5 is attributed to the larger thermodynamic driving force resulting from formation of strong CuII-oxo bonds in the ZSM-5 framework. © 2014 American Chemical Society.


Miao S.,Center for Surface Chemistry and Catalysis | Leeman H.,Center for Surface Chemistry and Catalysis | De Feyter S.,Celestijnenlaan | Schoonheydt R.A.,Center for Surface Chemistry and Catalysis
Chemistry - A European Journal | Year: 2010

The Langmuir-Blodgett (L- B) technique has been employed for the construction of hybrid films consisting of three components: surfactant, clay, and lysozyme (Lys). The surfactants are octadecylammonium chloride (ODAH) and octadecyl ester of rhodamine B (RhB18). The clays include saponite and laponite. Surface pressure versus area isotherms indicate that lysozyme is adsorbed by the surfactant- clay L-B film at the air-water interface without phase transition. The UV-visible spectra of the hybrid film ODAH- saponite-Lys show that the amount of immobilized lysozyme in the hybrid film is (1.3±0.2) ngmm-2. The average surface area (Ω) per molecule of lysozyme is approximately 18.2 nm2 in the saponite layer. For the multilayer film (ODAH-saponite-Lys)n, the average amount of lysozyme per layer is (1.0± 0.1) ngmm-2. The amount of lysozyme found in the hybrid films of ODAH-laponite- Lys is at the detection limit of about 0.4 ngmm-2. Attenuated total reflectance (ATR) FTIR spectra give evidence for clay layers, ODAH, lysozyme, and water in the hybrid film. The octadecylammonium cations are partially oxidized to the corresponding carbamate. A weak 1620 cm-1 band of lysozyme in the hybrid films is reminiscent of the presence of lysozyme aggregates. AFM reveals evidence of randomly oriented saponite layers of various sizes and shapes. Individual lysozyme molecules are not resolved, but aggregates of about 20 nm in diameter are clearly seen. Some aggregates are in contact with the clay mineral layers, others are not. These aggregates are aligned in films deposited at a surface pressure of 20 mNm-1. © 2010 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.


Heylen S.,Center for Surface Chemistry and Catalysis | Martens J.A.,Center for Surface Chemistry and Catalysis
Angewandte Chemie - International Edition | Year: 2010

Toxic CO concentrations can be detected by a very clear induced color change of the dirhodium complex 1 (see scheme) upon binding of CO, as reported by Esteban et al. Other atmospheric compounds such as H2O, CO 2, O2, CH4, SO2, NOx, and volatile organic compounds do not interfere with the CO sensing. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Feyand M.,University of Kiel | Mugnaioli E.,Johannes Gutenberg University Mainz | Vermoortele F.,Center for Surface Chemistry and Catalysis | Bueken B.,Center for Surface Chemistry and Catalysis | And 5 more authors.
Angewandte Chemie - International Edition | Year: 2012

A combined approach: A permanent highly porous bismuth-containing metal-organic framework (CAU-7) has been synthesized and its structure determined by a combination of electron diffraction, Rietveld refinement, and DFT calculations. The compound is catalytically active in the hydroxymethylation of furan (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Van Wouwe P.,Center for Surface Chemistry and Catalysis | Dusselier M.,Center for Surface Chemistry and Catalysis | Basic A.,Center for Surface Chemistry and Catalysis | Sels B.F.,Center for Surface Chemistry and Catalysis
Green Chemistry | Year: 2013

A productive and enantioselective hydrolysis of racemic mixtures of lactate esters with commercial Candida rugosa lipase was performed. This step contributes to a novel envisioned route for stereoselective PLA production by combining recent chemocatalytic developments with this biocatalytic contribution, foreseeing two separate l- and d-lactate enantiomer streams. A study of the hydrolysis kinetics identified an unexpected rate determining step at the origin of an unprecedented ester reactivity order. This journal is © 2013 The Royal Society of Chemistry.


Vanherck K.,Center for Surface Chemistry and Catalysis | Hermans S.,Center for Surface Chemistry and Catalysis | Verbiest T.,Catholic University of Leuven | Vankelecom I.,Center for Surface Chemistry and Catalysis
Journal of Materials Chemistry | Year: 2011

A new strategy is presented to achieve local heating of a membrane during a separation process, thereby increasing the membrane fluxes without affecting the membrane selectivity. By incorporating gold nanoparticles into a membrane structure, it is possible to heat the membrane during the separation process by light irradiation, applying the principle of photothermal heating. Gold nanoparticles are generated inside a premade cellulose acetate membrane. This composite material is characterized by electron microscopy and ultraviolet-visible spectroscopy. The effect of the photothermal heating of the gold nanoparticles on the membrane temperature, flux and selectivity is investigated by irradiation with a continuous wave argon-ion laser operating at 514 nm in a specially adapted filtration cell. It is shown for membranes containing a gold to polymer weight ratio of no more than 2% that water fluxes are increased by 15% while pure solvent fluxes can be increased up to 400% for ethanol and isopropanol. There is no significant effect of the photothermal heating on the rejection of the dye bromothymol blue in ethanol filtrations. To increase fluxes of a given membrane without lowering its selectivity is a highly desired but rarely found effect in membrane technology. The described method is most applicable for solvents with low thermal conductivity values, as energy loss by transfer to the medium is then occurring at a slow rate. © 2011 The Royal Society of Chemistry.


Miao S.,Center for Surface Chemistry and Catalysis | Leeman H.,Center for Surface Chemistry and Catalysis | De Feyter S.,Celestijnenlaan | Schoonheydt R.A.,Center for Surface Chemistry and Catalysis
Journal of Materials Chemistry | Year: 2010

Water-soluble protein monolayers have been prepared by spreading protein (lysozyme (Lys) and bovine serum albumin (BSA)) aqueous solutions over water and diluted clay (saponite) dispersions in a Langmuir-Blodgett (LB) trough. LB films of protein and hybrid protein-clay were prepared by vertical upstroke deposition at a desired surface pressure. Surface pressure-time (π-t) curves and surface pressure-area isotherms (π-A) indicate that the equilibrium time between the injection and compression plays an important role in forming a protein monolayer. Atomic force microscopy (AFM) suggests that heterogeneous films, consisting of regions of protein clusters and regions of saponite layers covered with protein clusters, are obtained. Both lysozyme and BSA accumulate particularly well at the edges of the saponite layers. The main difference is that the positively charged lysozyme is much more efficient in attracting negatively charged saponite layers at the air-water interface. The amount of lysozyme immobilized (nS) is 0.2-0.4 ng mm-2 for the water-lysozyme film and 0.5-0.6 ng mm-2 for the saponite-lysozyme film, as determined using UV-Vis spectroscopy. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirmed the presence of clay and proteins in the hybrid LB films. No significant change in the position of amide I or II bands was observed, suggesting little or no conformational changes upon immobilization of the proteins. © 2010 The Royal Society of Chemistry.


Van Der Veen M.A.,Center for Surface Chemistry and Catalysis | Van Der Veen M.A.,Catholic University of Leuven | Sels B.F.,Center for Surface Chemistry and Catalysis | De Vos D.E.,Center for Surface Chemistry and Catalysis | Verbiest T.,Catholic University of Leuven
Journal of the American Chemical Society | Year: 2010

For the first time, second-harmonic generation microscopy (SHGM) has been employed to study zeolites. Large ZSM-5 crystals filled with p-nitroaniline (PNA) dipoles have been visualized. It is shown that SHGM can discriminate between the straight b-pores and the sinusoidal a-pores of this zeolite, thus revealing the intergrown structure of these crystals. Moreover, it is shown that dipole chains are formed not only in the b-pores but also in the a-pores. PNA only assembles into dipole chains of parallel orientation in those pores that are directly accessible from the outer surface. The area in which this PNA ordering prevails is limited to a strip near the outer surface of the zeolite crystal. A rationalization for these two observations is offered. © 2010 American Chemical Society.


Schoonheydt R.A.,Center for Surface Chemistry and Catalysis
Chemical Society Reviews | Year: 2010

This critical review article discusses the characterization of heterogeneous catalysts by UV-VIS-NIR spectroscopy and microscopy with special emphasis on transition metal ion containing catalysts. A review is given of the transitions, that can be observed in the UV-VIS-NIR region and the peculiarities of catalytic solids that have to be taken into account. This is followed by a short discussion of the techniques that have been developed over the years: diffuse reflectance spectroscopy, UV-VIS microscopy, in situ or operando spectroscopy, the combination of UV-VIS spectroscopy with other spectroscopic techniques, with chemometrics and with quantum chemistry. In the third part of this paper four successes of UV-VIS-NIR spectroscopy and microscopy are discussed; (1) coordination of transition metal ions to surface oxygens; (2) quantitative determination of the oxidation states of transition metal ions; (3) characterization of active sites and (4) study of the distribution of transition metal ions and carbocations in catalytic bodies, particles and crystals (104 references). © 2010 The Royal Society of Chemistry.

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