Search results for "SELECTIVE OXIDATION"

Photocatalytic oxidation of aromatic alcohols to aldehydes in aqueous suspension of home prepared titanium dioxide: 2. Intrinsic and surface features…

2008

Some intrinsic electronic properties of home prepared (HP) TiO2 catalysts were investigated by diffuse reflectance spectroscopy and quasi-Fermi level measurements. These powders were used for carrying out the photocatalytic oxidation of benzyl alcohol to benzaldehyde and CO2 in water; the selectivity for aldehyde formation was enhanced by the addition of small amounts of ethanol, a typical hole trap. The values of band gap, valence band and conduction band edges are almost identical for all the HP samples in which anatase phase is predominant, whereas appreciable differences can be noticed for an HP sample containing high amount of rutile phase. A comparative ATR-FTIR study of the HP cataly…

Photocatalytic Selective Oxidation of 5-(Hydroxymethyl)-2-furaldehyde to 2,5-Furandicarbaldehyde in Water by Using Anatase, Rutile, and Brookite TiO2…

2013

5-(Hydroxymethyl)-2-furaldehyde (HMF) was selectively oxidized to 2,5-furandicarbaldehyde (FDC) in; aqueous medium by using home prepared (HP) anatase, rutile, and brookite TiO2 nanoparticles. HP samples were prepared via a sol-gel method by using TiCl4 as the TiO2 precursor. Commercial TiO2 catalysts were also used for, comparison. All samples were characterized by BET specific surface area, XRD, TGA, and SEM, and the reactivity results showed that HP catalysts are predominantly amorphous and give rise to selectivities toward FDC more than twice that of commercial and well crystallized catalysts.

Comparison between preparative methodologies of nanostructured carbon nitride and their use as selective photocatalysts in water suspension

2017

Carbon nitride photocatalysts have been prepared by different methodologies, such as chemical ultrasonic irradiation (sonochemical treatment), hydrothermal and ball milling and thermoexfoliation, and have been used for the selective oxidation of 5-hydroxymethyl-2-furaldehyde (HMF) to form 2,5-furandicarboxyaldehyde (FDC) in water suspension both under UV and natural solar irradiation. The physico-chemical features of the photocatalysts have been studied by X-ray diffraction, infrared spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, scanning electron microscopy, and specific surface area measurements. The results indicate that exfoliation of carbon nit…

Titania Photocatalysts for Selective Oxidations in Water

2011

Heterogeneous photocatalysis by polycrystalline semiconductor oxides is an unconventional technology that has been mainly applied for the degradation of organic and inorganic pollutants in both the vapor and liquid phase. The application of photocatalysis in synthetic routes has also been researched in recent years, demonstrating its viability as an alternative route in organic chemistry. This work illustrates the main findings in the application of heterogeneous photocatalysis to the oxidation of organic compounds dissolved in water, free of any organic co-solvent. Two main aspects of the oxidative process have been studied: the first one is the partial oxidation of various mono-substitute…

Production of Aldehydes by Oxidation in Aqueous Medium with Selective Recovery of the Product by Means of Pervaporation

2010

Synergy of Miniemulsion and Solvothermal Conditions for the Low-Temperature Crystallization of Magnetic Nanostructured Transition-Metal Ferrites

2017

Crystalline first-row transition-metal (Mn, Fe, Co, Ni, Cu, and Zn) ferrites were prepared by an unprecedented synergetic combination of miniemulsion synthesis and solvothermal route, pursuing unconventional conditions in terms of space confinement, temperature, and pressure. This synergy allowed for obtaining six different crystalline ferrites at much lower temperature (i.e., 80 °C) than usually required and without any postsynthesis thermal treatment. X-ray diffraction (XRD) revealed that analogous ferrites synthesized by miniemulsion at ambient pressure or in bulk (i.e., from an aqueous bulk solution and not in the confined space of the miniemulsion droplets) either at ambient pressure o…

DFT insights into the oxygen-assisted selective oxidation of benzyl alcohol on manganese dioxide catalysts

2020

Abstract The reactivity pattern of the MnO2 catalyst in the selective aerobic oxidation of benzyl alcohol is assessed by density functional theory (DFT) analysis of adsorption energies and activation barriers on a model Mn4O8 cluster. DFT calculations predict high reactivity of defective Mn(IV) sites ruling a surface redox mechanism, L-H type, involving gas-phase oxygen. Bare and promoted (i.e., CeOx and FeOx) MnOx materials with high surface exposure of Mn(IV) sites were synthesized to assess kinetic and mechanistic issues of the selective aerobic oxidation of benzyl alcohol on real catalysts (T, 333–363 K). According to DFT predictions, the experimental study shows: i) comparable activity…

Synthesis of vanillin in water by TiO2 photocatalysis

2012

Abstract The photoproduction of vanillin is studied in aqueous medium starting from trans-ferulic acid, isoeugenol, eugenol or vanillyl alcohol by using both commercial and home prepared TiO2 samples as photocatalysts and batch Pyrex photoreactors. The photo-oxidation at room temperature of these compounds produces vanillin with a selectivity ranging from 1.4 to 21 mol% with respect to the converted substrate. An investigation on the intermediates was performed in the case of trans-ferulic acid; for this substrate the most important intermediates were homovanillic acid, vanillyl mandelic acid, trans-caffeic acid, formic acid, acetic acid, and oxalic acid. The carbon mass balance, including …

Reaction products and pathways in the selective oxidation of C-2-C-4 alkanes on MoVTeNb mixed oxide catalysts

2010

[EN] The catalytic properties of MoVTeNbO catalysts during the selective oxidation of short chain alkanes and olefins (C-2-C-4) have been comparatively studied The main reaction products have been ethylene from ethane acrylic acid from propane maim anhydride from n-butane and methacrolein from isobutane FTIR studies of the adsorption of the main reaction products i e olefins and aldehydes over MoVTeNbO catalyst has been carried out Accordingly the reaction pathway is explained on the basis of the characteristics of the alkane fed the stability and reactivity of both the intermediates and the reaction products and the nature of the catalytic sites involved in each reaction (C) 2010 Elsevier …

A comparison between photocatalytic and catalytic oxidation of 2-Propanol over Au/TiO2-CeO2 catalysts

2016

Abstract Photocatalytic and catalytic oxidation of 2-propanol, representative of volatile organic compounds (VOC’s), were compared over mixed TiO 2 –CeO 2 -based catalysts. The effect of different amounts of CeO 2 and the presence of gold (1 wt%) on TiO 2 was investigated. In the photocatalytic oxidation CeO 2 had a negative effect on the performance towards the alcohol conversion of both TiO 2 –CeO 2 and Au/TiO 2 –CeO 2 catalysts, being Au/TiO 2 the most active system. On the contrary mixed TiO 2 –CeO 2 and Au/TiO 2 –CeO 2 samples showed a higher catalytic oxidation efficiency for 2-propanol conversion compared to the single oxides. In this case Au/CeO 2 catalyst had the best performance. …