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The impact of surface chemistry on the morphogenesis of maleic anhydride plasma polymer is investigated on silicon wafers with very well‐controlled surface chemistries (i.e., native oxide, hydroxyl‐rich, and alkyl‐rich). A particular attention is paid to characterize the early stages of growth. Two different morphologies of polymer films are obtained, depending on the hydrophilic or hydrophobic nature of the substrate surface, even though the chemical composition is very similar. Homogeneous and dense polymer films are formed on hydrophilic substrates due to the strong affinity of plasma species toward the surface. Elongated nanostructures resulting in a less dense polymer film grow on the hydrophobic surface, which are assumed to be the result of the low affinity of plasma species. [ABSTRACT FROM AUTHOR]

This contribution relates the behavior of Ti-SBA-15 catalysts in the sulfoxidation reaction with hydrogen peroxide under mild conditions (40-70 °C). Ti-SBA-15 samples with 1, 3 and 5 wt% of TiO2 have been prepared by grafting SBA-15 silica with Ti(OiPr)4 in ethanol followed by calcination. Due to their mesopores, the Ti-containing catalysts accommodated large molecules like methyl-phenyl-sulfide, diphenylsulfide and dibenzothiophene, which were selectively oxidized into their corresponding sulfoxides and sulfones. The turnover frequency was correlated with the amount of the tetrahedral Ti atoms in the catalyst. During the oxidation process performed in batch mode, with acetonitrile or ethanol as solvent, the catalyst topology and texture were preserved, but the nature of the Ti species suffered some changes. [ABSTRACT FROM AUTHOR]

Two series of TiO2–SiO2 composites have been prepared by post-synthesis impregnation of a TiO2 precursor onto SBA-15 silica matrices and subsequent thermal treatment at 400 °C in air. The influence of the textural properties of the SBA-15 and the TiO2 content was evaluated upon the dispersion of TiO2 and its crystallization in anatase. The morphology of the samples before and after impregnation was observed by electronic microscopy while the textural and structural properties were evaluated by different techniques such as XRD, nitrogen sorption manometry, and Raman spectroscopy. The quantity of crystallized anatase in the composites was determined by XRD quantification using an internal standard. The bandgap energy (Eg) of the composites was evaluated by diffuse reflectance spectroscopy and the results show that Eg decreases as a function of the titania content. The photoactivity of the prepared materials was evaluated by following the degradation of methyl orange (MO) in water under UV irradiation. For the same amount of catalyst, the MO degradation rate in the presence of the composites containing 28 and 44 wt% of crystallized anatase was found to be similar to the one in the presence of commercial fully crystallized anatase. [ABSTRACT FROM AUTHOR]

Solids composed of TiO2 nano-crystallites (10-40 wt %) dispersed in an SBA-15 matrix were synthesised and used as hydrodesulfurisation (HDS) active-phase supports. Well-dispersed polymolybdate species were detected by Raman spectroscopy on all the CoMo-based oxidic precursors. Undesirable bulk CoMoO4 mixed oxide was also detected on the surface of low-TiO2-content materials, which suggests the enhancement of the Mo oxidic species dispersion as a result of the presence of TiO2. After activation under H2/H2S, the obtained catalysts were tested in the HDS of thiophene. An optimum conversion was observed for the catalyst supported on the solid that contained 20 wt % TiO2, which outperformed the homologous samples supported on TiO2 and SBA-15. This clearly highlights the beneficial effect of using such nano-TiO2-SBA-15 composite supports, in which SBA-15 confers adequate textural properties to the system, and the active phase benefits from the dispersive effect of TiO2. [ABSTRACT FROM AUTHOR]

Abstract: The effect of Y-stabilized ZrO2 as support on the Pt dispersion and catalytic activity for the total oxidation of n-butane was investigated. From XRD, TEM and CO chemisorption measurements, Pt particles were found to be well dispersed with a size of ca. 10nm over the surface of ZrO2 and Y-stabilized ZrO2, when Pt supported catalysts were calcined at 600°C. Although Pt particles supported on ZrO2 were significantly sintered by high temperature calcination above 800°C, no aggregation of Pt particles was observed for Pt/Y–ZrO2. When the catalyst was calcined at higher temperatures, Pt catalysts supported on Y-stabilized ZrO2 showed higher activity than Pt/ZrO2 for the total oxidation of n-butane. The intrinsic activity, expressed in terms of turnover frequency (TOF), increased with the decrease in Pt dispersion, indicating that n-butane oxidation over Pt catalysts supported on Y-stabilized ZrO2 is a structure sensitive reaction. Y2O3 additive plays a role in improving the thermal stability of Pt particles through the metal–support interaction, while it does not alter the catalytic performance of Pt as catalytic active sites. [Copyright &y& Elsevier]

Abstract: This paper examines the effect of the addition of Y2O3 in ZrO2 support, on the support basicity, the Pt dispersion and the catalytic activity for the oxidation of n-C4H10. The ZrO2 supports, with and without 2mol% of Y2O3, and the supported-Pt catalysts calcined at 600 and 900°C have been studied. The basicity and acidity of ZrO2 determined by CO2-TPD and NH3-TPD was improved by Y2O3 dopant. Catalyst characterizations such as XRD, CO chemisorption and CO adsorption followed by IR spectroscopy demonstrated the positive effect of Y2O3 dopant to increase the stability of Pt particles even at high calcination temperatures, and so to increase the catalytic activity. [Copyright &y& Elsevier]

Abstract: Platinum based mesostructured SiO2 supported TiO2 nanoclusters (TiO2 content ranging from 10 to 50wt.%) were synthesized and characterized. Titania nanodomains (<4nm) dispersed in the silica porosity are obtained. Derived 1wt.% Pt/xTiO2-SiO2 nanocomposites were tested in the cyclohexane dehydrogenation reaction, a structure insensitive reaction to evaluate metal-support interaction. Pt/xTiO2-SiO2 nanocomposites display largely higher SMSI effect than measured over classical Pt/TiO2 P25 catalyst. While platinum particle size is found to be affected by the titania loading in the composite, similar SMSI effect is measured for all solids displaying similar TiO2 crystal size. Titania crystal size is evidenced as an important parameter allowing a control of the SMSI effect: the lower the crystal size, the stronger the metal-support interaction. [ABSTRACT FROM AUTHOR]

Abstract: Recently titania synthesis was reported using various structuration procedures, leading to the production of solid presenting high surface area but exhibiting moderate thermal stability. The study presents the synthesis of TiO2/SiO2 nanocomposites, a solid that can advantageously replace bulk titania samples as catalyst support. The silica host support used for the synthesis of the nanocomposite is a SBA-15 type silica, having a well-defined 2D hexagonal pore structure and a large pore size. The control of the impregnation media is important to obtain dispersed titania crystals into the porosity, the best results have been obtained using an impregnation in an excess of solvent. After calcination at low temperature (400°C), nanocomposites having titania nanodomains (∼2–3nm) located inside the pores and no external aggregates visible are obtained. This nanocomposite exhibits high specific surface area (close to that of the silica host support, even with a titania loading of 55wt.%) and a narrow pore size distribution. Surprisingly, the increase in calcination temperature up to 800°C does not allow to detect the anatase to rutile transition. Even at 800°C, the hexagonal mesoporous structure of the silica support is maintained, and the anatase crystal domain size is evaluated at ∼10nm, a size close to that of the silica host support porosity (8.4nm). Comparison of their physical properties with the results presented in literature for bulk samples evidenced that these TiO2/SiO2 solids are promising in term of thermal stability. [Copyright &y& Elsevier]