Oxidation of 1,3,5‐trichlorobenzene using advanced oxidation processes

The oxidation of 1,3,5‐trichlorobenzene (TCB) by ozone, ozone/UV, ozone/H₂O₂ and ozone/UV/H₂O₂ was studied. All studies were conducted in a continuously‐flowing completely mixed reactor (CFCMR), operated at steady‐state conditions using a hydraulic retention time of 10 minutes. The greatest removal of TCB using ozone/H₂O₂ treatment was achieved using a H₂O₂ concentration of 60 μM. At low pH values (approx. 2) ozone/UV performed significantly better than either ozone alone or ozone/H₂O₂. However, at circumneutral pH, the removal efficiencies of TCB by ozone/UV and ozone/H₂O₂ and ozone/UV/H₂O₂ were essentially equal (～ 97% for TCB). The removal efficiency of ozone alone was ～93% for TCB. At high pH (> 9) there was no advantage in supplementing ozone with either UV or H₂O₂ as the removal efficiencies for all processes studied were essentially equal.

The effect of humic acid and bicarbonate on the removal of TCB was studied. At 1.6 mg/L humic acid, 92–95% of the TCB was oxidized by the processes studied. The removal of TCB by ozone alone was significantly affected by the presence of bicarbonate ion. For the other processes at 10 mM bicarbonate, approximately 80% of the TCB was oxidized.     

Mode of action of oxidation‐active centres in Mo–V mixed oxides on the partial oxidation of an unsaturated aldehyde

The mode of action of the oxidation‐active centres in Mo–V mixed oxides on the selective oxidation of an unsaturated aldehyde was investigated by non‐steady‐state methods. Various oxidation‐active centres, differing in activity and selectivity, were identified by non‐steady‐state methods. In addition, the influence of the crystallinity of the Mo–V mixed oxides on the activity and selectivity properties were investigated. It was shown that, in contrast to crystalline samples, only X‐ray‐amorphous Mo–V mixed oxides contained selective oxidation centres. The measurements were used to derive a model based on the interaction of active centres with various redox properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hard amorphous nanocomposite coatings with oxidation resistance above 1000°C

Abstract

This article reports on two classes of novel hard amorphous coatings: (a) Si₃N₄/MeN_x coatings with high (≥50 vol.-%) content of Si₃N₄ phase; here Me=Zr, Ta, Ti, Mo, W, etc. and x=N/Me is the stoichiometry of MeN_x metal nitride phase, and (b) Si–B–C–N coatings with strong covalent bonds. These nanocomposites exhibit high thermal stability against crystallisation and high oxidation resistance, both at temperatures considerably exceeding 1000°C. Hard amorphous coatings were prepared using reactive magnetron sputtering. Properties of sputtered coatings were characterised using the following techniques: X-ray diffraction, electron probe microanalysis, Rutherford backscattering spectrometry, elastic recoil detection, high resolution transmission electron microscopy, selected area electron diffraction, atomic force microscopy, microhardness tester Fischerscope H 100, differential scanning calorimetry and thermogravimetric analysis. It was found that hard amorphous coatings of both new systems exhibit excellent oxidation resistance at high temperatures about 1500 and 1700°C for amorphous Si₃N₄/MeN_x and Si–B–C–N coatings respectively.     

Catalytic performance of advanced titanosilicate selective oxidation catalysts – a review

This review article aims to cover the state-of-the-art of titanosilicate catalysts for selective oxidations developed within past seven years. Many elaborated materials (e.g., layered and pillared titanosilicates, hierarchical composite materials, and others) have been prepared and thoroughly characterized; however, their catalytic properties have been usually investigated only using a single or few model substrates and compared with a benchmarking material. The main goal of this article is to summarize the novel catalysts and compare their catalytic performance with each other. The comparison is focused on epoxidation. In addition, phenol hydroxylation and sulphide oxidation are briefly covered.     

Anodic oxidation behaviour of Al–Ti alloys in acidic media

The anodic oxidation behaviour of Al–Ti alloys in several acidic solutions was investigated. The influence of conditions such as alloy composition, electrolytic solution, electrolyte temperature and formation current density on the formation rate of oxides on Al–Ti alloys and the dielectric properties of the anodic films were analysed. It was shown that the oxide formation rate for the Al–Ti alloy containing 54 at % aluminium was the highest and the dielectric property of its anodic oxide was also the best. In addition, by means of several surface analytical techniques, the chemical composition of the films were determined as (TiO₂) _n (Al₂O₃) _m . AES (Auger electron spectroscopy) profiling analysis data showed that Al–Ti alloys had preferential oxidation behaviour, that is, the aluminium was oxidized preferentially.     

Catalytic properties of SrSn1−xSbxO3 in methanol oxidation

Ceramic model catalyst materials of general formula SrSn_1–x Sb _x O₃ are synthesised by solid state reaction. X-ray diffraction shows the materials to be single phase over the composition range 0 x0.085, with a second phase, identified as SrSb₂O₅, being produced at higher antimony doping levels. XPS, Auger electron spectroscopy and valence band photoemission show strong segregation of Sb to the surface of the material even within the single phase regime. The catalytic properties of the materials are examined using methanol oxidation as a test reaction. The activity and selectivity to formaldehyde production shown by these materials is found to be strongly correlated with the attainment of the bulk solubility limit of Sb in the SrSnO₃ perovskite host.     

Continuous oxidation of benzyl alcohol in “supercritical” carbon dioxide

Supercritical (dense) carbon dioxide has been applied as solvent for the partial oxidation of benzyl alcohol with molecular oxygen in a fixed-bed reactor. High rate and good selectivity to benzaldehyde (93–97%) has been achieved with 0.5 wt% Pd/alumina or 0.5 wt% Pd/C, at around 100C and 100 bar, using only moderate excess of oxygen. The by-product benzoic acid has an autocatalytic effect on the hydration of benzaldehyde, and the subsequent oxidative dehydrogenation leads to benzoic acid, and benzyl benzoate by esterification. Promotion of Pd by Pb improves the selectivity. No catalyst deactivation or metal leaching has been observed. The method provides reasonable yields at much lower temperature than that applied in conventional gas phase oxidation, showing a potential for the synthesis of thermolabile, water-insoluble aromatic aldehydes.     

Lacunary silicotungstic heteropoly salts as high-performance catalysts in oxidation of cyclopentene

The development of polyoxometalates for olefin oxidation is critical to achieving the green chemical process of the C5 fraction further processing. Di-lacunary silicotungstic anions were easily obtained by continuously adjusting the p H instead of the traditional step-by-step method, which exhibited excellent performance in the catalytic oxidation of cyclopentene(CPE) to aldehydes or alcohols. The 93.69% CPE conversion and 97.15% total product selectivity(41.38% for glutaraldehyde(GA) and 55.77%...     

Unique photocatalytic oxidation reactivity and selectivity of TiO₂-graphene nanocomposites

Mesoporous TiO(2)-graphene nanocomposites are fabricated in high yield via two successive steps: (1) hydrothermal hydrolysis of Ti(SO(4))(2) in an acidic suspension of graphene oxide to gain TiO(2)-graphene oxide nanocomposites; (2) UV-assisted photocatalytic reduction of graphene oxide to get the TiO(2)-graphene nanocomposites. The anatase TiO(2) nanocrystals with a crystallite size of 10-20 nm are densely packed and supported on meshy graphene sheets with close interfacial contacts, which is confirmed by transmission electron microscopy (TEM) together with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Although a low graphene loading (0-2 wt%) slightly influences the textural properties (including the crystallite size, specific surface areas, and pore volume etc.), the incorporation of graphene in TiO(2)-graphene nanocomposites greatly increases the adsorption capacity towards azo dyes such as MO and MB, which is possibly associated with their unique surface properties. Significantly, the incorporated graphene exerts combined effects on the adsorption and charge transfer dynamics in TiO(2)-graphene nanocomposites, which together endow them with good photocatalytic reactivity and tunable photocatalytic selectivity in decomposing MO and MB in aqueous solution.     

Influence of particle size distribution on oxidation behaviour of β-SiAlON powder

Abstract

Kinetic equation of oxidation process with diffusion controlled step in solid product layer is deduced, in which the influence of particle size distribution of β-SiAlON on the reaction rate has been taken into account. This equation was applied to the oxidation of β-SiAlON powder, and fitted well with the experimental data. Comparisons with the results offered by the model using one and two effective radiuses are also included, from which it can be seen that the model considering particle size distribution is the best for describing the kinetics of powder system. The activation energy ΔE of oxidation of β-SiAlON powder is also obtained, which is 258 kJ mol^?1.     

PVP-assisted Sn-Ti microspheres for the efficient B–V oxidation of cyclohexanone

Journal of Porous Materials - New Sn-Ti microspheres were first successfully synthesized by a PVP-assisted sol-gel method in this paper, and their performance in the B–V oxidation of...     

Partial oxidation of toluene by O2 over mesoporous Cr–AlPO

The synthesis of mesoporous Cr–AlPO was carried out under hydrothermal conditions. Characterisation of the catalyst was done with low angle XRD, N₂ adsorption, UV–VISDRS, ESR and thermal analysis. The catalytic activity was tested for partial oxidation of toluene with molecular oxygen in vapour phase. It was observed that Cr–AlPO functions both as acid and redox catalyst.     

Iron antimony oxide selective oxidation catalysts – an inelastic neutron scattering study

The inelastic neutron scattering spectra of allyl iodide (3-iodopropene, CH₂=CHCH₂I) and allylpalladium chloride, and allyl iodide dosed onto activated iron(III) oxide and iron antimonate catalysts at room temperature have been determined to characterise the adsorbed allyl species. The spectra are energy loss vibrational spectra in the range 16–4000 cm⁻¹. Allyl iodide is not decomposed on the surface and interacts through the localised C = C bond, more strongly with iron antimonate than with iron(III) oxide. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermally stable ceria–zirconia catalysts for soot oxidation by O2

Ce–Zr mixed oxides calcined at 1000 °C are more active catalysts for soot oxidation than pure CeO₂ calcined at the same temperature, both in loose and tight contact between soot and catalyst. 1000 °C sinterised-CeO₂ presents a very low surface area (2 m²/g), a large crystal size (110 nm) and a lack of surface redox properties. Ce–Zr mixed oxides present higher BET surface areas (typically 17–19 m²/g), smaller crystal sizes and enhanced redox properties. The Zr molar fraction does not affect appreciably the catalytic activity of Ce–Zr mixed oxides in the range studied (Zr molar fraction from 0.11 to 0.51).     

Rate oscillations during partial oxidation of methane over chromel–alumel thermocouples

A chromel–alumel thermocouple has been found to catalyse the methane/oxygen reaction, the main products being CO, H₂ with some CO₂ and H₂O. Regular oscillations in both reactants, products and temperature have been observed at temperatures around 700C. Similar behaviour has been obtained using nickel wires.     

Effect of supports in hydrogen sulfide oxidation on vanadium−based catalysts

Selective oxidation of hydrogen sulfide to sulfur was carried out over V₂O₅ and V−Sb−O mixed−oxide catalysts supported on TiO₂, ZrO₂ and −Al₂O₃. TiO₂−supported catalysts exhibited the highest sulfur yield and the highest areal rate. Catalyst reducibility was studied by temperature−programmed reduction. This revised version was published online in July 2006 with corrections to the Cover Date.     

β-Cyclodextrin promoted oxidation of primary amines to nitriles in water

A facile, efficient and substrate-selective oxidation of the primary amines with NaClO as oxidant catalyzed by β-cyclodextrin (β-CD) has been developed in water for the first time, and the behavior of β-cyclodextrin that catalyzed the primary amines to nitriles in water was investigated. It was found that the primary amines which could form host-guest complexes with β-cyclodextrin were oxidized to nitriles with excellent yields at ambient temperature. The results show that β-cyclodextrin worked not only as a solubilizing agent but also as a catalyst in these reactions.     

Theoretical and experimental study on the inhibition of jet fuel oxidation by diarylamine

Antioxidants addition is believed as a facile and effective way to improve jet fuel thermal oxidation stability. However, amine antioxidants, as one of the most important antioxidants, have not received sufficient attention in the field of jet fuel autoxidation yet. Herein, the inhibition efficiency and mechanism of decane and exo-tetrahydrodicyclopentadiene(THDCPD) oxidation by di-4-tert-butylphenylamine(diarylamine) was experimentally and theoretically investigated. The results show that diary...     

Pd oxidation under UHV in a model Pd/ceria–zirconia catalyst

A model planar catalyst was prepared by depositing Pd onto a thick (few m) film of ceria–zirconia in ultrahigh vacuum (UHV), and the oxidation state of Pd and its support was determined by X-ray photoelectron spectroscopy, following thermal treatments in UHV, oxygen, or carbon monoxide. It was found that Pd could be oxidized simply by heating the catalyst in UHV, indicating that transfer of oxygen from the support to the metal is both thermodynamically favorable and facile.