The rotational molecular dynamics of water confined to nanoporous molecular sieves of a regular hexagonal (SBA-15) and of a foamlike pore structure was studied by dielectric spectroscopy in the frequency range from 10(-2) to 10(9) Hz and in a broad temperature interval. Two relaxation processes were observed: the process at lower frequencies is related to water molecules forming a layer, which is strongly adsorbed at the pore surface, whereas the relaxation process at higher frequencies is assigned to fluctuations of water molecules situated close to the center of the pore. The relaxation times of the low-frequency process for both materials and of the high-frequency process for the SBA-15 material have an unusual saddlelike temperature dependence, reported here for the first time. To describe this temperature dependence, a model developed for water confined to nanoporous glasses by Ryabov et al. [J. Phys. Chem. B 2001, 105, 1845] was applied, which considers two competing effects. The characteristic features of these two competing processes were compared with those reported for other porous systems.

Confinement of 4n-octyl-4′-cyanobiphenyl to nanoporous molecular sieves with hexagonal structure of cylindrical pores or with cellular structure is studied. It was found by differential scanning calorimetry and broadband dielectric spectroscopy that composites with the pores completely filled with liquid crystal show phase transitions characteristic for bulk, while the partially filled samples do not show these transitions. Thermogravimetric, differential thermal analysis and in situ infrared spectroscopic investigations have indicated first time that the dealkylation and oxidation of the confined liquid crystal is quite possible inside the nanopores of these molecular sieves, at temperatures much lower than for the bulk.

Molecular dynamics of water confined to some molecular sieves is Studied by broadband dielectric spectroscopy (10(-2) to 10(9) Liz). Faujasite as well as molecular sieves with hexagonal cylindrical pores or cellular structure were used as confining matrix. It was found that the mean relaxation time of confined water has unusual non-monotonic saddle-like temperature dependence. Such temperature dependence was interpreted using a model recently developed by Ryabov et al. [J. Phys. Chem. B 2001, 105, 1845] to analyze the dynamics of water in nanoporous glasses. The unusual behavior is the result Of two competing processes: orientational fluctuations the water molecules following all Arrhenius-like temperature dependence and the formation of the defects necessary for this reorientation. The number of defects decreases with increasing the temperature. The temperature dependence of the relaxation time has been proven to be a quite fundamental phenomenon characteristic for water in confining geometries. The defects involved in the dynamics of confined water might be related to the presence of OH groups as defects of the confining framework.

Investigations of the properties of supported nano-scale Au catalysts in the partial oxidation of three different polyvalent oxygen substituted compounds are presented. The relations between Au particle size and catalytic properties of Au/Al2O3 in the partial oxidation of ethylene glycol to glycolic acid as model reaction are discussed. Moreover, influences of the nature of the alumina support and the applied precipitation agent on the catalyst properties were studied. Furthermore, the potential of these catalysts for the industrial interesting partial oxidation of glyoxal to glyoxylic acid was checked. However, it seems that the oxidation of glyoxal is dominated by a CC rupture leading to formic acid, mainly. Finally, the excellent selectivity of gold supported on alumina or titania in the partial oxidation of aldehyde groups of saccharides to carboxylic groups is briefly presented.

Static oxygen adsorption and hydrogen pulse titration of chemisorbed oxygen were checked and successfully used as tools for characterisation of the dispersity and surface area of Au/Al2O3 catalysts tested in the oxidation of ethylene glycol. Using a stoichiometry of Aus:O=2 a good agreement was obtained between the average gold particle size calculated from oxygen chemisorption results and the particle size preferentially observed by TEM. A correlation of the catalytic activity with the oxygen adsorption of Au/Al2O3 catalysts having different Au dispersity and content showed a steady increase of the rate of the glycolic acid formation with increasing oxygen chemisorption and Au surface area, respectively. No differences in the selectivity of the reaction were observed with low- and high-disperse Au/Al2O3 catalysts, a selectivity to glycolic acid higher than 95% was obtained on all the samples. Therefore, we could clearly demonstrate that the selective oxidation of ethylene glycol to glycolic acid is not a structure-sensitive reaction, i.e. this reaction is not restricted to a defined gold particle size, as for example in the epoxidation of propylene over Au/TiO2.

Composites containing 4-n-octyl-4′-cyanobiphenyl (8CB) either confined to nanopores of molecular sieves with very large pores or coating silica nanoparticles of aerosil type at high silica-to-8CB ratios are investigated by IR spectroscopy. Band shape analysis was performed in wavenumber regions in which the peaks due to CN stretching, CH stretching and CH out-of-plane vibrations appear. Some of molecules confined to molecular sieves show spectroscopic features characteristic to a bulk-like 8CB matter located in the centre of the pores or in the inter-grain space. Other features of the IR spectra are due to 8CB molecules located in the surface layer, mostly forming hydrogen bonds between their CN groups and surface OH groups. Another part of the 8CB molecules in the surface layer may also interact by π electrons of the aromatic rings. Hydrogen bonding is less hindered for the molecules of the surface layers onto aerosil particles than inside pores of the molecular sieves. Comparison is also made with the case of composites based on molecular sieves with small pores.

Molecular dynamics of a nematic liquid crystal, 4n-octylcyanobiphenyl, confined to two types of SBA-type nanoporous molecular sieves were studied by broadband dielectric spectroscopy in order to obtain information about the liquid crystal-surface interactions. The temperature interval of the dielectric measurements was large, covering all the states of the bulk liquid crystal. It is found that there are several relaxation processes covering the large frequency range. A bulk-like relaxation comes from the liquid crystal molecules located in the center of the pores, which rather do not feel the effect of the pore walls. Another relaxation comes from the molecules located in the surface layer. The latter process is much slower than the bulk-like relaxation. The differences observed between the dynamic behavior of the liquid crystal confined to the two types of nanoporous materials are related to pore size, pore shape and liquid crystal-surface interactions.

This work presents some results obtained by confining octylcyanobiphenyl (8CB) to the pores of two SBA-15 type host materials: a silica SBA-15 (pores of 10.2 nm) and an aluminum containing AlSBA-15 (pores of 7.5 nm). The LC molecules were loaded inside the pores from a solution in acetone, in a percentage higher than 70% from the maximum possible loading. It was observed that the 8CB molecules confined to molecular sieves may preserve the phase transitions characteristic for the bulk LC provided that the confining pores are sufficiently large, as offered by SBA materials. However, present guest-host interactions play an important role in these phase transitions. Such a behavior is at variance with the 8CB confined to Controlled Porous Glass with the same pore dimensions, for which the bulk-like phase transitions can be always observed.

Aluminas with Fe2O3 particles finely divided in the Al2O3 matrix were prepared via a crystalline precursor derived from ammonium dawsonite and its calcination. The precursors with Fe content between 1 and 10 wt% were synthesized by reaction of ammonium hydrogen carbonate with mixtures containing aluminium ammonium sulfate and ferric ammonium sulfate. The characterization of the as-synthesized and calcined products by chemical analysis, XRD, EPR, Mossbauer, TEM and adsorption measurements shows that all the Fe3+ ions are incorporated into the structure of dawsonite when the Fe content is low and that the calcined materials with micropores and mesopores (maximum 30-40 Angstrom) also contain very small Fe2O3 particles (<10 nm) at higher Fe contents.

Catalysts consisting of boria supported on Al2O3, TiO2, ZrO2 and MgO were studied in the partial oxidation of propane at 550 degrees C. The highest propene yield amounted to 22 % (S = 45 - 48%) on B2O3/Al2O3; in addition, yields to C-1-C-3 oxygenates of up to 8 % were achieved (S = 28 %). Surface and bulk composition of the B-Al-O catalysts were investigated using B-11 NMR, XRD and XPS to elucidate the factors determining propane conversion, product distribution and catalyst deactivation. It was shown that the coordination of boron influences catalyst activity; trigonal BO3 species being present in both crystalline and amorphous phases are active in the dehydrogenation of propane to propene. The water formed during the reaction causes the loss of these species most probably as boric acid. The catalyst consisting of amorphous boria revealed high initial activity but resulted in faster volatilization of boria compared to a catalyst consisting of crystalline B2O3 and aluminium berates. Oxygenates formation was favoured in the presence of an Al6B8O21 phase.

The hydrothermal stability of high-silica Y zeolites dealuminated by Al/Si substitution may be increased by alumination of the crystal surface. The externally introduced non-framework aluminum species — alkali aluminosilicates or alumina — cover the surface where the water molecules attack the terminal OH groups and energy-rich Si-O-Si bonds. An alkaline and combined acid/alkaline pathway of alumination are suggested. A reinsertion of aluminum into the zeolite lattice could not be observed.

Al,SiOxgels have been prepared by reaction of different inorganic aluminium compounds with silicic acid. Characterization by chemical analysis,27Al MAS NMR spectroscopy and adsorption measurements shows that the gels obtained from a mixture (pH ca. 3) of basic aluminium chlorides and silicic acid in water are porous and contain tetrahedrally coordinated aluminium in the framework. IR spectroscopy and TPDA measurements confirm that Bronsted and Lewis acid sites are present in the gels. Finally, catalytic activity was found in hex-1-ene isomerization.

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Faujasite (FAU) and its hexagonal analog (EMT) was investigated in the catalytic cracking of n-heptane. Measurements were conducted with Aerosil-200 bound catalysts in an integral fixed bed reactor at 723 K. Catalytic activity is related to the concentration of Brønsted acid sites of the zeolite framework. Catalytic behaviour of dealuminated and subsequently acid leached varieties evidences that extra-framework aluminium species formed during dealumination contribute to catalysis. The distribution within the spectrum of the products of reaction clearly demonstrates that pathways producing alkenes and free hydrogen are involved in the scission of the parent hydrocarbon.

Zeolite faujasite type with hexagonal structure (EMT) and zeolite faujasite types with cubic structure (FAU) were synthesized with crown ethers as templating agents. The Si/Al ratio of the as-synthesized samples was determined to 3.7. The samples were dealuminated by steaming at 773, 873 and 1073 K, respectively. A part of the dealuminated samples was treated with diluted acid to extract the non-framework aluminum. Nature and concentration of the acid centres were estimated by IR spectroscopy and TPDA measurements. From N-2 isotherms follows that the extracted samples undergo a partial damage of the structure. It seems that the EMT samples are more stable in the process of steaming and extraction with diluted acid.

Durch Addition von Vinyl- und H-substituierten Doppelvierringkieselsäurederivaten hergestellte Organokieselsäurepolymere werden thermonalytisch mit TG-, DTA-and DSC-Messungen charakterisiert. Der thermooxidative Abbau der vier untersuchten Polymere erfolgt in mehreren Schritten: Oxidation der (Si−H)-Gruppen, Oxidation der Ethylenbrücken (Si−CH2−CH2−Si) und Oxidation der (Si−CH3)-Gruppen, jeweils unter Bildung von neuen (Si−O−Si)-Bindungen.29Si-NMR-spektroskopische Ergebnisse stützen die Deutung des Reaktionsablaufsablaufes. Thermoanalytische Untersuchungsmethoden können erfolgreich zur Charakterisierung von Organokieselsäurepolymeren eingesetzt werden.

Inorganic-organic polymers were synthesized by additive reaction of vinyl-, allyl-, and H-silylated double four-ring (D4R) silicic acids and polymeric silicic acids. The structure and properties of the hybrid polymers were investigated by means of 29Si NMR spectroscopy, thermoanalysis and BET nitrogen adsorption measurements. Using the defined vinylsilylated D4R silicicacid [(CH2CH)(CH3)2Si]8Si8O20 and the corresponding H-silylated compound [(CH3)2HSi]8Si8O20 as precursors, the additive reaction results in a microporous polymer with a ordered Si8O20 substructure. The structural units are connected by six-membered bridges. Shorter (four-membered) or longer (seven-membered) bridges between D4R cages lead to non-porous polymeric materials. The connection of water-glass-derived silicic acid units by six-membered bridges similarly leads to porous polymers with specific surface areas of 500 m2/g. For the preparation of the porous hybrid polymers a new, simple two-step reaction route is described.

By thermal analysis and 29Si NMR spectroscopy the thermal behaviour and structural changes of two different types of inorganic-organic polymers with defined double four-ring silicic acid units (Si8O20) were characterized. Polymer 1, prepared from the organic silicic acid precursors [(CH3)2HSi]8Si8O20 (Q8M8H) and [CH2=CH(CH3)2Si]8Si8O20 (Q8M8V), preserves the double four-ring structure up to 350°C Higher temperatures lead to structural reorganizations of the SiO4 tetrahedra forming at 900°C a structure similiar to amorphous silica. Polymer 2, synthesized by condensation reaction of the new organic silicic acid precursor [CH3O)3Si(CH2)3OC(O)CH(CH3)CH2Si(CH3)2]8Si8O20, shows with 37% uncondensed SiOH groups a remarkable high content of silanol groups caused by sterical hindrances.