Search results for "Heterogeneou"
showing 10 items of 461 documents
The role of H2O in the photocatalytic oxidation of toluene in vapour phase on anatase TiO2 catalyst
1999
Abstract Photocatalytic oxidation of toluene has been carried out in a gas–solid regime by using polycrystalline anatase TiO2 in a fixed-bed continuous reactor. Air containing toluene and water vapours in various molar ratios was fed to the photoreactor irradiated by a medium pressure Hg lamp. Toluene was mainly photo-oxidised to benzaldehyde, and small amount of benzene, benzyl alcohol and traces of benzoic acid and phenol were also detected. In the presence of water, no decrease of photoreactivity was observed at steady-state conditions. By removing water vapour from the feed, the conversion of toluene to benzaldehyde was almost completely inhibited, and an irreversible deactivation of th…
Pumice-Supported Nickel Catalysts
1997
A series of nickel catalysts supported on pumice was prepared by precipitation and impregnation techniques. The influence of the calcination and reduction temperatures on the structural properties such as lattice parameters and particle dimensions of the oxide precursors and of the reduced catalysts was investigated by X-ray diffraction measurements. The effect of structural changes on the catalytic activity in the hydrogenation of carbon monoxide has been evaluated. The turnover frequencies, as well as product distributions, are discussed in terms of the influence of the support properties and of its interaction with the metal. Changes of the C2+yield over CH4yield ratio versus nickel disp…
Total oxidation of propane using nanocrystalline cobalt oxide and supported cobalt oxide catalysts
2008
Abstract Supported and unsupported nanocrystalline cobalt oxides have been shown to be extremely efficient catalysts for the total oxidation of propane. Total conversion with a high stability has been achieved at reaction temperatures as low as 250 °C. In the present work, a comparison between the catalytic performance of bulk and alumina-supported nanocrystalline cobalt oxide catalysts has been made. The influence of crystallite size, nature of the support (alpha, gamma and mesoporous alumina) and cobalt loading, has been probed. Unsupported cobalt oxide catalysts were more active than any supported cobalt oxide catalysts. The catalytic activity was mainly dependent on the crystallite size…
Oxidation of aminodiols mediated by homogeneous and heterogeneous TEMPO
2004
The conversion of amino diols to aminohy- droxy acids by oxidation of the primary hydroxy group mediated by homogeneous and heterogeneous TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl radi- cal) is reported. The synthesis uses NaOCl as primary oxidant and TEMPO, either dissolved in the homoge- neous phase or entrapped in a sol-gel matrix, as cata- lytic mediator. Homogeneous TEMPO is suitable for the oxidation of aliphatic methylamino diols, while the hybrid organic-inorganic silica sol-gel catalysts are more selective mediators for the oxidation of ben- zylic amino diols like the potent antibiotic chloram- phenicol which, under homogeneous conditions, are unselectively oxidized to benzoic ac…
Deep oxidation of propane using palladium–titania catalysts modified by niobium
2008
Abstract Pd/TiO 2 catalysts modified by niobium have been prepared and tested for the complete oxidation of propane. The catalysts have been characterised by BET, XRD, laser Raman spectroscopy, XPS, DRS and TPR. The incorporation of niobium into Pd/TiO 2 catalysts resulted in a marked increase in the catalytic activity compared to the Nb-free Pd/TiO 2 catalysts, and the activity increased as the niobium and/or palladium loading increased. The addition of Nb significantly modified the nature of the palladium and niobium species. There was a marked increase in the oxygen mobility after niobium addition. This could not only promote the presence of palladium species in a totally oxidized state …
Heterogeneous borrowing hydrogen reactions with Pd/C and ZnO: Diol scope
2017
Abstract A borrowing hydrogen reaction with different diols was employed for the preparation of complex beta- gamma- or epsilon-amino alcohols from p-toluidine and tetrahydroquinoline with the aim of better understanding the applicability of the Pd/C ZnO heterogeneous catalyst.
Nanolayered Cobalt-Molybdenum Sulfides as Highly Chemo- and Regioselective Catalysts for the Hydrogenation of Quinoline Derivatives
2018
[EN] Herein, a general protocol for the preparation of a broad range of valuable N-heterocyclic products by hydrogenation of quinolines and related N-heteroarenes is described. Interestingly, the catalytic hydrogenation of the N-heteroarene ring is chemoselectively performed when other facile reducible functional groups, including alkenes, ketones, cyanides, carboxylic acids, esters, and amides, are present. The key to successful catalysis relies on the use of a nanolayered cobalt-molybdenum sulfide catalyst hydrothermally synthesized from earth-abundant metal precursors. This heterogeneous system displays a tunable composition of phases that allows for catalyst regeneration. Its catalytic …
Highly Active Co3O4-Based Catalysts for Total Oxidation of Light C1–C3 Alkanes Prepared by a Simple Soft Chemistry Method: Effect of the Heat-T…
2021
9 figures, 2 tables.
Friedel-Crafts catalytic alkylations using rare earth-based mineral supports
1998
Abstract Rare earth halides supported on mineral supports (K10 montmorillonite and silica) were investigated as catalysts for Friedel-Crafts alkylations. This project concerns the replacement of the widely used Lewis acid AlCl3 in Friedel-Crafts reactions by environmentally friendly catalysts in that they circumvent the production of aluminum waste. The catalytic activity of these heterogeneous catalysts was established in a series of alkylations of aromatic compounds.
Lignin-based activated carbon-supported metal oxide catalysts in lactic acid production from glucose
2021
In this study, heterogeneous biomass-based activated carbon-supported metal oxide catalysts were prepared and tested for lactic acid production from glucose in aqueous solution. Activated carbons were produced from hydrolysis lignin by chemical (ZnCl2) or steam activation and modified with a nitric acid treatment and Sn, Al, and Cr chlorides to obtain carbon-based metal oxide catalysts. The modification of the carbon support by nitric acid treatment together with Sn and Al oxides led to an increase in lactic acid yield. The highest lactic acid yield (42%) was obtained after 20 minutes at 180 °C with the Sn/Al (5/2.5 wt.%) catalyst on steam-activated carbon treated by nitric acid. Reusabilit…