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Ferdi Schüth

Publications and source records attributed to Ferdi Schüth.

At least 19 recordsLinked to original sources
PubMed2007

Preparation of high-surface-area zinc oxide with ordered porosity, different pore sizes, and nanocrystalline walls.

Transition-metal-oxide materials possessing ordered mesoporosity have recently attracted significant research interest due to their numerous potential applications. Among them, ordered mesoporous zinc oxide (ZnO) is a very tempting material because of the importance of ZnO in heterogeneous catalysis. Here, first results of the preparation of ordered mesoporous ZnO materials by using different templates are reported. Porous materials with high surface area, different pore sizes, and nanocrystalline ZnO walls were obtained. Furthermore, we compare the two fundamental templating techniques, involving liquid crystals or ordered mesoporous carbon materials as templates. Regarding the formation of mesoporous ZnO, it was evident that the hard-matter carbon template is superior.

Journal Article↗
PubMed2006

Tuning the mesostructures of vinyl silica by adjusting the micellar curvature.

In our previous study (Wang, Y. Q.; Yang, C.-M.; Zibrowius, B.; Spliethoff, B.; Lindén, M.; Schüth, F. Chem. Mater. 2003, 15, 5029), mesoporous vinyl-functionalized silica (vinyl silica) with hexagonal P6mm and cubic Ia3d structures has been synthesized at different loadings of vinyl groups and at different concentrations of sodium chloride when triblock copolymer P123 was used as a template. Our further investigations presented in this article reveal that at a loading of 10% vinyl groups, well-ordered cubic Ia3d structure was obtained at a low concentration of Na2SO4 (0.5 M) and the hexagonal structure was produced at 1.0 M NaCl. When NaNO3 was used as the inorganic salt, the hexagonal structure was still maintained even at a salt concentration of 2.0 M. The result is in accordance with the Hofmeister series order (salting-out effect): SO4(2-) > Cl- > NO3(-). The lowering of the acidity also induced the formation of the cubic Ia3d structure. At 20% loading, hexagonal structure can be obtained by adding the more hydrophilic Pluronic F127 (EO106PO70EO106) to the acidic solutions of P123, but the hexagonal structure cannot be produced with pure P123 under the synthesis conditions investigated. All of these results can be rationalized through hydrophilic-hydrophobic balance and the change in micellar curvature. Furthermore, 10% mercaptopropyl-functionalized mesoporous silica with cubic Ia3d structure was designed and synthesized successfully with the assistance of an inorganic salt (NaCl) in an acidic solution of P123, which is the first example of mercaptopropyl-functionalized large-pore mesoporous silica with high loadings.

Anions↗
PubMed2006

Dependence of dissociation pressure upon doping level of Ti-doped sodium alanate--a possibility for "thermodynamic tailoring" of the system.

Pressure-concentration isotherms have been recorded for NaAlH(4) with different doping levels of titanium. It is well known that titanium accelerates the hydrogenation and dehydrogenation reactions in this system. Our studies have shown that the titanium doping also significantly alters the thermodynamics of the system, which is demonstrated by the change of the dissociation pressure with doping level. This can be explained by changes in the systems energy by dilution of the TiAl-alloy present after doping: Such an alloy forms as a result of the doping reaction. Aluminum generated during the dehydrogenation reaction dilutes this alloy, which gives an additional contribution to the free energy of the system.

Aluminum Compounds↗
PubMed2006

Monitoring temporal evolution of silicate species during hydrolysis and condensation of silicates using mass spectrometry.

The first stages of solid-state formation from solution can be crucial in determining the properties of the resulting solids. We are trying to approach prenucleation reactions of silicates from an aqueous solution containing tetraalkylammoniumhydroxides (TAAOH) and tetraalkoxysilanes (TAOS) by analyzing hydrolysis and condensation using electrospray mass spectrometry (ESI MS). Time-resolved measurements were performed using different reactor systems to show the stepwise hydrolysis of the silanes and subsequent condensation of silicate monomers via oligomers to form larger units. We approached the precipitation point by varying the pH and the concentrations of the reactants. The results show the evolution of different silicate species occurring during condensation. No defined molecular entities were identified at pH values close to precipitation, which suggests that under the conditions used, solids are probably not formed from defined building blocks.

Journal Article↗
PubMed2006

Support effect in high activity gold catalysts for CO oxidation.

In this work, we present a detailed study concerning the evaluation of the metal-support interaction in high activity gold catalysts for CO oxidation. Using the colloidal deposition method, model catalysts were prepared, which allow the isolation of the effect of the support on the catalytic activity. Prefabricated gold particles were thus deposited on different support materials. Since the deposition process did not change the particle sizes of the gold particles, only the influence of the support could be studied. TiO2, Al2O3, ZrO2, and ZnO were used as support materials. Catalytic tests and high resolution transmission electron microscopy clearly show that the support contributes to the activity. However, our results are not in line with the distinction between active and passive supports based on the semiconducting properties of the oxidic material. The most active catalysts were obtained with TiO2 and Al2O3, while ZnO and ZrO2 gave substantially less active catalysts. Furthermore, the effect of other important parameters on the catalytic activity (i.e., particles size distribution, calcination temperature, and aging time for a Au/TiO2 catalyst) has also been studied. Using this preparation route, the catalysts show high-temperature stability, size dependent activity, and a very good long-term stability.

Journal Article↗
PubMed2006

Exchange anisotropy in nanocasted Co3O4 nanowires.

Antiferromagnetic Co3O4 nanowires with an average diameter of about 8 nm have been synthesized by using the nanocasting route. The nanowires were characterized by powder X-ray diffraction, transmission electron microscopy, and a superconducting quantum interference device magnetometer. The magnetic measurements show a unidirectional exchange anisotropy accompanied by an enhancement of the field-cooled coercivity at low temperature. These effects suggest the presence of an exchange interaction between the antiferromagnetic core and the surface spins. A strong dependence of the exchange field on the magnitude of the cooling field and a training effect have been observed. The dependence of exchange bias field on temperature reveals the important role played by the antiferromagnetic core in the exchange coupling.

Journal Article↗
PubMed2005

Hierarchically structured monolithic silicalite-1 consisting of crystallized nanoparticles and its performance in the Beckmann rearrangement of cyclohexanone oxime.

In this study, we present a synthetic pathway for the fabrication of self-supporting zeolite monoliths consisting of crystallized nanoparticles. A resorcinol-formaldehyde-based organic aerogel is used as a template, and silicalite-1 is used as the zeolite example. The silicalite-1 monoliths obtained consist of individual well-defined zeolite nanocrystals with sizes of 30-40 nm. The monoliths exhibit a high mechanical stability and have hierarchical porosity, with micropores within the zeolite particles, a mesopore system formed by the packing of the nanoparticles, and a macropore system on the monolith level. Such monolithic zeolites show high selectivity typically above 80% to epsilon-caprolactam combined with a high rate of reaction of 0.46 g(caprolactame)/(g(catalyst).h) in the Beckmann rearrangement of cyclohexanone oxime.

Carbon↗
PubMed2005

High surface area, mesoporous, glassy alumina with a controllable pore size by nanocasting from carbon aerogels.

A strategy to synthesize amorphous, mesoporous alumina by nanocasting has been developed, involving carbon aerogel as a hard template and aluminum nitrate solution as an alumina precursor. The alumina generated exhibits small, transparent granules with a 3-6 mm diameter and has inherited the three-dimensional network structure of the carbon template. The mesopore surface area of the alumina can be as high as 365 m2 g(-1), and the pore volume reaches 1.55 cm3 g(-1) after calcination at 600 degrees C in air for 8 h. The pore parameters can be varied within a certain range by variation of the carbon aerogel template and the loading amount of the alumina precursor. At high loadings, the obtained glassy alumina clearly has a bimodal pore size distribution in the mesopore range.

Journal Article↗
PubMed2004

Synthesis and characterization of nanocast silica NCS-1 with CMK-3 as a template.

Nanocast silica (NCS-1) was synthesized by a casting process by employing the mesoporous carbon CMK-3 (the replica of SBA-15) as a template, tetraethoxysilane (TEOS) as the silica source, and hydrochloric acid (HCl) as the catalyst. The ordered carbon template was removed by employing different methods, such as calcination, thermal treatment followed by calcination, and controlled combustion. According to XRD and TEM characterization, NCS-1 exhibits an ordered structure with hexagonal symmetry and retains the morphology of the original SBA-15 used for the synthesis of CMK-3 over two replication steps on the nanometer scale. This demonstrates the well-connected porosity in CMK-3 type carbon, which can be used as a mold to synthesize mesostructured materials. The nitrogen adsorption isotherms generally show type IV shape, indicating mesoporous characteristics. The structure of NCS-1 is strongly influenced by variables of the nanocasting process, such as the loading amount of silica, hydrolysis temperature, and carbon removal methods. The surface area, pore size, and pore volume of NCS-1 can be tuned to a certain range by varying these parameters.

Journal Article↗