8 results on '"DRUV-VIS"'
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2. Synthesis of Cu/SiO2(MCM-41) mesostructured catalysts. Effect of the preparation method on the textural properties and chemical structure.
- Author
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Cuesta Zapata, Pablo M., Miranda, José F., Orellana, Francisco, Gonzo, Elio, and Bonini, Norberto A.
- Subjects
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CHEMICAL properties , *MCM-41 (Mesoporous material) , *MESOPOROUS materials , *CHEMICAL structure , *SOL-gel materials , *ION exchange (Chemistry) , *MATERIALS testing - Abstract
Two Cu/SiO 2 mesoporous materials (Cu-MCM-41) were synthesized, one by the ion exchange (IE) post-synthesis method and the other, by the sol-gel (SG) method by co-precipitation of copper and silica (Cu-MCM-41) in the cetyltrimethylammonium bromide (CTAB) presence. The effects of the synthesis method on these materials were analyzed. They were characterized by XRD, N 2 adsorption-desorption, TEM, DRUV–vis, FTIR, TPR, XPS, and FTIR with both, CO and pyridine adsorbed. Using the SG method, an MCM-41 material with a uniform mesoporous structure (D p ≈ 35 Å), and a specific surface area (S BET) of 800 m2.g-1, was obtained. With the IE method and due to the partial collapse of the SiO 2 -MCM-41 mesoporous structure used as support, a material with a lower S BET (560 m2.g-1) was produced. The Cu in the SG synthesized material was mainly constituted by SiO-[CuO] n -CuOSi polymeric species and small CuO agglomerates. On the other hand, in the IE material, the copper was in the form of isolated SiO–Cu–OSi monomers, SiO–Cu–O–Cu–OSi dimers, and only a low proportion of SiO-[CuO] n -CuOSi oligomers. The catalytic activity of both materials was tested against the 2-propanol (2-PrOH) dehydrogenation in the gas phase. The reaction rate of the IE synthesized material was an order of magnitude higher than that prepared by the SG method. This behavior was attributed to the presence of SiO–Cu+ pair formed by the reduction of SiO–Cu–O–Cu–OSi dimmers present in the material prepared by IE; in contrast with the CuO aggregates obtained by the SG method. [Display omitted] • Ion exchange method causes the partial collapse of the MCM-41 mesoporous structure. • Co-precipitation method conducts to an ordered Cu-MCM-41 material. • Ion exchange method favors a high Cu dispersion by grafting C2+ ions into the pores. • The Cu+2 dimeric species are responsible for the high dehydrogenation activity of the IE materials. • In the Sol-Gel materials, Cu is mainly in the external surface of the pores as CuO precursors. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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3. Acid sites development on Cr3+/SiO2 catalysts obtained by the sol–gel method and hydrothermal treatment: Effect of calcination temperature.
- Author
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Cuesta Zapata, Pablo M., Parentis, Mónica L., Gonzo, Elio E., and Bonini, Norberto A.
- Subjects
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CHROMIUM , *CATALYSIS , *SOL-gel processes , *THERMAL analysis , *CALCINATION (Heat treatment) , *PROPANOLS , *FOURIER transform infrared spectroscopy - Abstract
Highlights: [•] The sol–gel and hydrothermal treatment let to obtain Cr3+ incorporated to SiO2 support. [•] The Cr3+ ions are stable and resistant to segregation in air up to 350°C. [•] These Cr3+ ions produce Lewis acid sites that catalyze the 2-propanol dehydration. [•] The Cr6+ ions formed after in air calcination (450°C) develops weak Brönsted sites. [•] 2,6-Lutidine adsorption lets to quantify the Lewis and Brönsted sites by FTIR. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
4. Chemoselective oxidation of 2-thiomethyl-4,6-dimethyl-pyrimidine on nanostructured tantalum oxides
- Author
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Budoace, S., Cimpeanu, V., Pârvulescu, V., Centeno, M.A., Grange, P., and Pârvulescu, V.I.
- Subjects
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OXIDATION , *NANOSTRUCTURES , *TANTALUM , *TRANSITION metals - Abstract
A series of tantala–silica catalysts (15 wt.% Ta2O5) were prepared by sol–gel from tantalum and silica ethoxides. These syntheses were carried out using two families of quaternary ammonium salts, CnH2n+1(CH3)3NBr (
n=14 , 16, 18) and (CnH2n+1)4NBr (n=10 , 12, 16, 18) were used as surfactants. The catalysts were characterized by adsorption–desorption isotherms of N2 at 77 K, XRD, SAXS, DRUV-Vis, py and CDCl3-FTIR, and XPS. The catalytic tests were carried out in dioxane, methanol or CHCl3, and indicated that both conversion and selectivity depend on the size of tantalum nanoxide. Leaching investigation showed that part of Ta is extracted from the network, but it segregates on the support as Ta2O5. [Copyright &y& Elsevier]- Published
- 2004
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5. Acid sites development on Cr3+/SiO2 catalysts obtained by the sol–gel method and hydrothermal treatment: Effect of calcination temperature
- Author
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Monica Liliana Parentis, Elio Emilio Gonzo, Pablo Martín Cuesta Zapata, and Norberto Alejandro Bonini
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Sol-Gel ,2,6-Lutidine ,Nanotecnología ,Chemistry ,Process Chemistry and Technology ,Inorganic chemistry ,Druv-Vis ,Cr/Sio2 ,INGENIERÍAS Y TECNOLOGÍAS ,Catalysis ,Hydrothermal circulation ,law.invention ,Ingeniería Química ,Adsorption ,Dehydration reaction ,law ,Otras Ingeniería Química ,Calcination ,Otras Nanotecnología ,Lewis acids and bases ,Partial oxidation ,Brønsted–Lowry acid–base theory - Abstract
Cr/SiO2 catalysts (4-8% Cr, w/w), obtained from Cr(III) salts and tetraethylortosilicate (TEOS), were prepared by the sol-gel method. After TEOS hydrolysis in ammoniacal solution (pH: 9.5), the gel was treated under hydrothermal conditions at 120-220 C. The solids were characterized by N 2 sorptometry, TG-DTA, DRUV-vis, XRD, and FTIR. In vacuum or N 2 atmosphere, Cr3+ ions were stable up to 450 C. However, calcination in air promotes the partial oxidation of Cr3+ to Cr 6+ as the temperature increases from 200 to 450 C. The amount of Cr6+ formed depends on the temperature of the hydrothermal treatment. 2,6-Lutidine adsorption allows to determine the evolution, with respect to calcination temperature, of both Lewis and Brönsted acid centers. Cr 3+ ions were related to the presence of Lewis sites, and Cr 6+ ions to the development of weak Brönsted acid sites. Accordingly, the 2-propanol dehydration reaction rate shows an increase when the catalysts are treated in N2 at 450 C, while catalysts calcined in air develop a lower acidity. The dehydration reaction is attributed to the presence of Lewis acid centers. Fil: Cuesta Zapata, Pablo Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones para la Industria Química. Universidad Nacional de Salta. Facultad de Ingeniería. Instituto de Investigaciones para la Industria Química; Argentina Fil: Parentis, Monica Liliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones para la Industria Química. Universidad Nacional de Salta. Facultad de Ingeniería. Instituto de Investigaciones para la Industria Química; Argentina Fil: Gonzo, Elio Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones para la Industria Química. Universidad Nacional de Salta. Facultad de Ingeniería. Instituto de Investigaciones para la Industria Química; Argentina Fil: Bonini, Norberto Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Investigaciones para la Industria Química. Universidad Nacional de Salta. Facultad de Ingeniería. Instituto de Investigaciones para la Industria Química; Argentina
- Published
- 2013
6. Synthesis and Characterization of High-Surface-Area Silica-Titania Monoliths
- Author
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Adriano Zecchina, Alessandro Damin, Silvia Bordiga, and Andriy P. Budnyk
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Anatase ,Materials science ,Inorganic chemistry ,chemistry.chemical_element ,symbols.namesake ,RAMAN ,ANATASE ,TI(IV) CENTERS ,Reactivity (chemistry) ,Physical and Theoretical Chemistry ,Fourier transform infrared spectroscopy ,Sol-gel ,TS-1 CATALYSTS ,X-ray absorption spectroscopy ,SOL-GEL ,XANES ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,chemistry ,Chemical engineering ,FTIR ,DRUV-Vis ,symbols ,TI COORDINATION ,Raman spectroscopy ,Mesoporous material ,Titanium - Abstract
Hybrid SiO2–TiO2 mesoporous monoliths were synthesized via sol–gel method. The water for hydrolysis of titanium precursor has been obtained in situ via esterification reaction between acid and alcohol without use of additional agents. The titania content in the samples has been varied from 2 to 40 M% molar content with respect to silica. The nitrogen adsorption isotherms showed that monoliths containing 2 M% of Ti retain a large surface area and micropores with size peaking in the 1 to 2 nm interval. For larger Ti content, a bimodal average micropores distribution is observed. The surface area decreases for titania content larger than 10 M%. The Raman spectra taken with excitation lines in the 244–785 nm interval and the UV–vis measurements demonstrate that in the 2 M% sample Ti is atomically dispersed and fully incorporated in the SiO2 framework and that the local structure is similar to that of titanium silicalite. This conclusion is further confirmed by XAS measurements. Also, the reactivity toward hyd...
- Published
- 2012
7. Spectroscopic studies of composite obtained from solid state reaction between a mononuclear vanadium(IV) complex and kaolinite
- Author
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Tatiana Lopez Fernandez, Marciela Scarpellini, Antonio S. Mangrich, Annelise Casellato, Ana P. Mangoni, and Edivaltris I. P. De Rezende
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Stereochemistry ,Chemistry ,Solid-state ,General Chemistry ,Solid material ,law.invention ,lcsh:Chemistry ,Paramagnetism ,lcsh:QD1-999 ,law ,DRUV-VIS ,Physical chemistry ,Amine gas treating ,composite ,Electron paramagnetic resonance ,Spectroscopy ,Second derivative ,EPR spectroscopy - Abstract
p. 257-261 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-08-12T15:41:53Z No. of bitstreams: 1 Edivaltris I. P. De Rezende.pdf: 341853 bytes, checksum: 451bfcd6b86617e1880b27e0dbad8c26 (MD5) Made available in DSpace on 2014-08-12T15:41:53Z (GMT). No. of bitstreams: 1 Edivaltris I. P. De Rezende.pdf: 341853 bytes, checksum: 451bfcd6b86617e1880b27e0dbad8c26 (MD5) Previous issue date: 2012 The use of probes, such as paramagnetic species diluted in diamagnetic materials in EPR spectroscopy, and mathematical tools such, as the Kubelka-Munk function in DRUV-VIS spectroscopy are strategies in the analysis of complex mixtures of solid materials. The results obtained here show that the solid state reaction between the complex, [VO(acac)(BMIMAPY)] [ClO4], BMIMAPY = [(bis(1-methylimidazole-2-yl)methyl)(2-(pyridyl-2-yl)ethyl) amine] and acac = acetilacetonate, with kaolinite turns possible to obtain anisotropic EPR spectrum of the complex with a reasonable level of resolution. The study by DRUV-VIS using the method of second derivative mode of the Kubelka-Munk function revealed new complex structural arrangements, a solid hitherto unknown.
- Published
- 2012
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8. Chemoselective oxidation of 2-thiomethyl-4,6-dimethyl-pyrimidine on nanostructured tantalum oxides
- Author
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UCL - Autre, Budoace, S, Cimpeanu, V., Parvulescu, V, Centeno, MA, Grange, Paul, Parvulescu, VI, 7th European Workshop Meeting on Selective Oxidation, UCL - Autre, Budoace, S, Cimpeanu, V., Parvulescu, V, Centeno, MA, Grange, Paul, Parvulescu, VI, and 7th European Workshop Meeting on Selective Oxidation
- Abstract
A series of tantala-silica catalysts (15 wt.% Ta2O5) were prepared by sol-gel from tantalum and silica ethoxides. These syntheses were carried out using two families of quaternary ammonium salts, CnH2n+1(CH3)(3)NBr (n = 14, 16, 18) and (CnH2n+1)(4)NBr (n = 10, 12, 16, 18) were used as surfactants. The catalysts were characterized by adsorption-desorption isotherms of N-2 at 77 K, XRD, SAXS, DRUV-Vis, py and CDCl3-FTIR, and XPS. The catalytic tests were carried out in dioxane, methanol or CHCl3, and indicated that both conversion and selectivity depend on the size of tantalum nanoxide. Leaching investigation showed that part of Ta is extracted from the network, but it segregates on the support as Ta2O5. (C) 2004 Elsevier B.V. All rights reserved.
- Published
- 2004
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