Kinetic study of crystalization of amorphous TiO2

Práce se zabývá přípravou amorfního TiO2 z roztoku tetraizopropoxidu. Připravené vzorky byly charakterizovány metodami TPD, TG, XRD, BET. Pomocí DSC byl studován proces krystalizace v amorfním TiO2.Dokončená práce s úspěšnou obhajobo

Characterization of vanadium sites on vanadium-containing mesoporous silica catalysts and their catalytic behaviour in propane ODH

Parameters that affect the catalytic behaviour of vanadium-containing mesoporous silicas in oxidative dehydrogenation reaction of propane are mainly aggregation state of surface VOx species and reducibility of vanadium species. Type and conditions of synthesis have big impact on the nature of vanadium species and, therefore, influence significantly catalytic properties. Two vanadiumcontaining mesoporous silica catalysts were synthesized by different techniques (including direct synthesis from hydrogel containing vanadium precursor and wet impregnation of SBA-15 mesoporous silica by vanadyl acetylacetonate) and their physico-chemical and catalytic properties were studied and compared. Direct synthesis of vanadosilicate led to catalysts with non-uniform mesoporosity, but exhibiting better spreading of vanadium on the surface resulting in species with lower degree of polymerization compared to impregnated catalyst. It is reflected in higher iso-conversional selectivity of directly synthesized catalyst towards propene

Role of methods and conditions of preparation of vanadium species supported on lamellar zeolite MCM-36 in their catalytic behaviour in oxidative dehydrogenation of propane

In this work, we report successful preparation of hierarchical VOx-MCM-36 catalysts. Lamellar pillared zeolitic support (MCM-36) was prepared from layered precursor of MCM-22P zeolite by swelling and pillaring. Vanadium was introduced into MCM-36 support by different methods (including conventional impregnation and ion exchange) by means of different precursors and synthesis conditions. Textural properties of prepared catalysts were characterized by nitrogen adsorption-desorption isotherms, the concentration of vanadium was determined by X-ray fluorescence and vanadium complex speciation was investigated by diffuse reflectance UV-vis spectroscopy, hydrogen temperature programmed reduction (H2 -TPR), electron paramagnetic resonance (EPR) and Fourier transform infrared (FTIR) spectroscopy. Effect of synthesis method and conditions on catalytic behaviour was tested in the oxidative dehydrogenation of propane at 540 °C. The vanadium is present in oxidation state IV, instead of usual oxidation state V, in the cases of the catalyst with low content of vanadium. The best selectivity to propene with 13 % of conversion (43.9 %) was obtained when the acid center was neutralized with potassium cations and the content of vanadium was 2 wt %

Nanostructure of hyaluronan acyl-derivatives in the solid state

Acylované deriváty hyaluronanu (acyl-HA) jsou perspektivní materiály pro biomedicínské aplikace. V závislosti na délce acylové skupiny a stupni substituce mohou mít tyto deriváty formu polymerů rozpustných ve vodě se schopností samouspořádání až po materiály ve vodném prostředí nerozpustné. Již bylo studováno chování acyl-HA v roztocích, avšak málo pozornosti jim bylo zatím věnováno v pevném stavu, přestože jsou významné pro takové aplikace, jako je například výroba zdravotnických prostředků. Proto jsme s pomocí rentgenového rozptylu a elektronové mikroskopie zkoumali nanostrukturu acyl-HA v pevném stavu. Sada vzorků zahrnovala různé substituenty, stupně substituce a molekulové hmotnosti. Získaná data ukázala, že všechny studované materiály acyl-HA obsahují struktury o rozměrech v řádu nanometrů, které nejsou přítomné v nemodifikovaném hyaluronanu. Rozměr nanostruktur se zvyšoval s délkou acylové skupiny, zatímco vliv stupně substituce a molekulové hmotnosti byl zanedbatelný. Zjištěná nanostrukura pravděpodobně odpovídá distribuci hydrofobních domén v hydrofilní matrici nemodifikovaného hayluronanuAcyl derivatives of hyaluronan (acyl-HA) are promising materials for biomedical applications. Depending on the acyl length and the degree of substitution, these derivatives range from self-assembling watersoluble polymers to materials insoluble in aqueous environments. The behaviour of acyl-HA was studied in solution, but little attention was paid to the solid state, despite its importance for applications such as medical device fabrication. We thus used X-ray scattering and electron microscopy to explore the solidstate nano-structure of acyl-HA. The set of samples included various substituents, substitution degrees and molecular weights. The obtained data showed that all studied acyl-HA materials contained structures with dimensions on the order of nanometers that were not present in unmodified HA. The size of the nanostructures increased with the acyl length, while the degree of substitution and molecular weight had negligible effects. We suggest that the observed nanostructure corresponds to a distribution of hydrophobic domains in a hydrophilic matrix of unmodified HA segment