Anna E. Lewandowska

Oxidative properties of niobium-containing mesoporous silica catalysts

Abstract Oxidative properties of MCM-41 molecular sieves containing niobium in the framework or/and in the extra framework positions were studied by means of H2-TPR, FTIR+NO, ESR techniques and were tested in the oxidation of dibutyl sulphide with hydrogen peroxide. The application of various Nb-sources in the synthesis of NbMCM-41 materials allows the estimation of a role of oxalate ions in the generation of active centres. The activity of Nb-containing mesoporous molecular sieves in the oxidation of thioethers with H2O2 requires the presence of Nb–O− species in the framework. The growth of a concentration of niobium (from Si/Nb=32 to Si/Nb=16) results in the decrease of the number of active centres due to the release of oxygen during the activation procedure. Niobium species in the extra framework positions of MCM-41 catalysts are not active in the dibutyl sulphide oxidation with H2O2 unless they are leached to the solution. Oxidative centres on the catalyst surface cause the formation of nitrite/nitrate species after the adsorption of NO.

Epoxidation of cyclohexene on Nb-containing meso- and macroporous materials

Abstract Various niobium-containing meso- and macroporous materials were prepared and characterised by means of XRD and H2-TPR techniques, scanning electron microscopy (SEM), and sorption measurements. They were tested in the liquid phase oxidation of cyclohexene to epoxide with hydrogen peroxide. The effect of various parameters such as a nature of solvent, material structure, atmosphere on the activity and selectivity of the reaction was studied. NbMCM-41 and NbSM-2 materials are highly active in the epoxidation.

Nb-containing mesoporous molecular sieves — a possible application in the catalytic processes

Abstract Nb-containing MCM-41 mesoporous molecular sieves were modified with ammonium and copper cations and characterised by ESR, FTIR and H 2 -TPR techniques. The prepared materials were tested in the following catalytic reactions: NO decomposition, reduction of NO with NH 3 , hydrosulphurisation of methanol, and oxidation of thioethers with hydrogen peroxide. The oxidising character of the NbMCM-41 mesoporous molecular sieves was revealed, which induces their application as very active and selective catalysts in the oxidation of thioethers with H 2 O 2 to sulphoxides. HNbMCM-41 samples, which exhibit Lewis acidity after dehydroxylation, are selective catalysts in the methanethiol synthesis in the reaction between methanol and hydrogen sulphide. Copper modified NbMCM-41 sieves indicate the higher reducibility of cupric cations than that observed when AlMCM-41 matrix for copper is used. The higher reducibility of cupric ions does not cause a higher activity in the catalytic NO decomposition.

Reutilization of Cr-Y zeolite obtained by biosorption in the catalytic oxidation of volatile organic compounds

This work aims at the reutilization of a Cr-loaded NaY zeolite obtained by biorecovery of chromium from water as catalyst in the oxidation of volatile organic compounds (VOC). Cr-NaY catalysts were obtained after biosorption of Cr(VI) using a bacterium, Arthrobacter viscosus, supported on the zeolite. The biosorption experiments were conducted at different pH values in the range 1-4. The catalysts were characterized by several techniques, namely ICP-AES, SEM-EDS, XRD, XPS, Raman, H(2)-TPR and N(2) adsorption. The zeolite obtained at pH 4 has the highest content of chromium, 0.9%, and was selected as the best catalyst for the oxidation of different VOC, namely ethyl acetate, ethanol and toluene. For all VOC tested, the catalyst with chromium showed higher activity and selectivity to CO(2), in comparison with the starting zeolite NaY. The presence of chromium shifted also the reaction pathways. In terms of selectivity to CO(2), the following sequence was observed: ethyl acetate>toluene>ethanol.

The possible use of mesoporous molecular sieves for deodorisation

Mesoporous molecular sieves of MCM-41 type, thanks to their very high sorption capacity, are useful sorbents for odours such as organic sulfur compounds. Two processes for the regeneration of sorbents are proposed in this paper: i) dehydrosulfurisation (DHS) and ii) oxidation with H2O2. They were studied using butanethiol and dibutyl sulfide as the representatives of the sulfur compounds. In the DHS reaction, NiAlMCM-41 catalysts are the best due to their high activity and selectivity to H2S and C4 hydrocarbons. The Ni-cation exchanged material is much more active and selective to the desired products than the Ni- impregnated sample. The high activity in the oxidation of dibutyl sulfide to sulfoxide with H2O2 has been found on Nb-containing materials. These catalysts are easily regenerated recovering the previous activity.

NbMCM-41 mesoporous molecular sieves in oxidative dehydrogenation of ethane and propane

It has been evidenced that the dissolution of niobium in silica mesoporous matrix significantly increases the catalytic effectiveness in the oxidative dehydrogenation of alkanes as compared with unsupported Nb2O5.

Characterisation of iron containing molecular sieves—the effect of T-element on Fe species

Surface properties of Fe-modified micro-(ZSM-5) and mesoporous (MCM-41) molecular sieves exhibiting various T elements (Si, Al, Nb) in the framework have been studied by means of XRD, adsorption of N 2 , ESR, and FTIR spectroscopy combined with the adsorption of NO. Fe oxide species, tetrahedral coordinated Fe 3+ and isolated Fe 2+ cations have been identified depending on the kind of the matrix. The presence of niobium in the mesoporous framework enhances the oxidative properties of iron modified samples.

Stress Transfer Quantification in Gelatin-Matrix Natural Composites with Tunable Optical Properties

This work reports on the preparation and characterization of natural composite materials prepared from bacterial cellulose (BC) incorporated into a gelatin matrix. Composite morphology was studied using scanning electron microscopy and 2D Raman imaging revealing an inhomogeneous dispersion of BC within the gelatin matrix. The composite materials showed controllable degrees of transparency to visible light and opacity to UV light depending on BC weight fraction. By adding a 10 wt % fraction of BC in gelatin, visible (λ = 550 nm) and UV (λ = 350 nm) transmittances were found to decrease by ∼35 and 40%, respectively. Additionally, stress transfer occurring between the gelatin and BC fibrils was quantified using Raman spectroscopy. This is the first report for a gelatin-matrix composite containing cellulose. As a function of strain, two distinct domains, both showing linear relationships, were observed for which an average initial shift rate with respect to strain of -0.63 ± 0.2 cm(-1)%(-1) was observed, followed by an average shift rate of -0.25 ± 0.03 cm(-1)%(-1). The average initial Raman band shift rate value corresponds to an average effective Youngs modulus of 39 ± 13 GPa and 73 ± 25 GPa, respectively, for either a 2D and 3D network of BC fibrils embedded in the gelatin matrix. As a function of stress, a linear relationship was observed with a Raman band shift rate of -27 ± 3 cm(-1)GPa(-1). The potential use of these composite materials as a UV blocking food coating is discussed.

The use of niobium containing mesoporous molecular sieves in the liquid phase oxidation

Abstract Activity and selectivity of Nb containing MCM-41 materials in the liquid phase oxidation of methyl-phenyl sulphide (MeSPh) and hydroxylation of phenol with H2O2 are shown in this paper. Various reaction pathways depending on the nature of substrates and solvents are considered. The activity of NbMCM-41 samples is compared with that of VMCM-41 and bimetallic NbVMCM-41 materials. Vanadium, in the solid and in the liquid after leaching, is not active in the oxidation of MeSPh. The effect of solvents, reaction temperature, and a nature of the catalyst on the decomposition of H2O2 have been considered. Too fast H2O2 decomposition in water at 353 K is disadvantageous in the phenol hydroxylation on both NbMCM-41 and NbVMCM-41. MeSPh adsorption on Nb containing materials protects niobium leaching with H2O2 to methanol. The activity of NbMCM-41 in MeSPh oxidation can be correlated, to some extent, with the presence of defects, and that of NbVMCM-41 - with the formation of defects resulted from vanadium leaching.

27-P-09-Niobium leaching from the catalysts applied in the sulfoxidation of thioethers with hydrogen peroxide

Publisher Summary This chapter presents the study of micro- and mesoporous materials containing niobium (Nb) in the framework or extra framework positions in the oxidation of dibutyl sulphide with hydrogen peroxide (H 2 O 2 ). Leaching of Nb from the solid to the liquid phase is considered. Some of the catalysts prepared through the impregnation with Nb salts show some leaching of Nb to the liquid phase and the oxidation partially occurs homogeneously in the liquid phase. The reaction proceeds mainly on the catalyst surface when the mesoporous molecular sieves containing Nb in the framework are used.