On the role of monomeric vanadyl species in toluene oxidation over V2O5/TiO2 catalysts: a kinetic study using the TAP reactor

Catalytic C-H aerobic and oxidant-induced oxidation of alkylbenzenes (including toluene derivatives) over VO2+ immobilized on core-shell Fe3O4@SiO2 at room temperature in water

Direct C–H bond oxidation of organic materials, and producing the necessary oxygenated compounds under mild conditions, has attracted increasing interest. The selective oxidation of various alkylbenzenes was carried out by means of a new catalyst containing VO²⁺ species supported on silica-coated Fe₃O₄ nanoparticles using t-butyl hydroperoxide as an oxidant at room temperature in H₂O or solvent-free media. The chemical and structural characterization of the catalyst using several methods such as FTIR spectroscopy, XRD, FETEM, FESEM, SAED, EDX and XPS showed that VO²⁺ is covalently bonded to the silica surface. High selectivity and excellent conversion of various toluene derivatives, with less reactive aliphatic (sp³) C–H bonds, to related benzoic acids were quite noticeable. The aerobic oxygenation reaction of these alkylbenzenes was studied under the same conditions. All the results accompanied by sustainability of the inexpensive and simple magnetically separable heterogeneous catalyst proved the important criteria for commercial applications.

A highly efficient, recoverable, sustainable, economic and eco-friendly catalyst containing VO²⁺ species supported on SiO₂@Fe₃O₄ nanoparticles for selective oxidation of alkylbenzenes using TBHP or O₂ at room temperature in H₂O or solvent-free media.

Photocatalytic Oxidation of α-C-H Bonds in Unsaturated Hydrocarbons through a Radical Pathway Induced by a Molecular Cocatalyst

To improve the photocatalytic oxidation of α-C-H bonds in unsaturated hydrocarbons, N-hydroxyphthalimide (NHPI) was used as a molecular cocatalyst with CdS as the photoabsorber. Compared with previously reported photocatalysts involving solid cocatalysts, metal-free NHPI offers better sustainability in addition to the significantly enhanced performance as cocatalyst. The photogenerated holes were transferred into the more active phthalimide-N-oxyl radical (PINO) by reacting with NHPI. In this way, α-C-H bond oxidation was significantly improved through the activation by PINO; even for the sluggish toluene oxidation, the apparent quantum efficiency was as high as 36.5 %. The effects of substrates/NHPI concentration ratio, reaction temperature, and time as well as the reaction intermediates were comprehensively studied. It was possible to identify ketones/aldehydes as the primary products, and overoxidation was controlled by adjusting the substrates/NHPI concentration ratio and reaction time. Thus, the radical path induced by the NHPI-PINO redox pair is an efficient alternative to boost the sluggish photocatalytic oxidation of α-C-H bonds.

Mechanism of heterogeneous catalytic oxidation of organic compounds to carboxylic acids

The results of studies on the mechanism of heterogeneous catalytic oxidation of organic compounds of different chemical structure to carboxylic acids are analyzed and generalized. The concept developed by Academician G.K.Boreskov, according to which the direction of the reaction is governed by the structure and bond energy of surface intermediates, was confirmed taking the title processes as examples. Quantitative criteria of the bond energies of surface compounds of oxidizable reactants, reaction products and oxygen that determine the selective course of the reaction are presented.

The bibliography includes 195 references.

Forty years of temporal analysis of products

A detailed understanding of reaction mechanisms and kinetics is required in order to develop and optimize catalysts and catalytic processes. Temporal analysis of products (TAP) is an instrument capable of providing such understanding.

TAP study of toluene total oxidation over a Co3O4/La-CeO2 catalyst with an application as a washcoat of cordierite honeycomb monoliths

The total oxidation of toluene was studied over a Co₃O₄/La-CeO₂ catalyst in a Temporal Analysis of Products (TAP) set-up in the temperature range 713 K to 873 K in the presence and absence of dioxygen.

Degradation of Toluene Using Modified TiO2 as Photocatalysts

Volatile organic compounds (VOCs), especially toluene as the typical indoor air pollutants, are toxic and environmentally persistent whose removal is undoubtedly becoming increasingly urgent matter over these years. Titania is one of the most promising photocatalysts for the degradation of organic compounds, whereas the large band gap of titania and massive recombination of photogenerated charge carriers limit its overall photocatalytic effciency. These defects can be tackled by modifying the electronic band structure of titania including various strategies like metal deposition, non-metal atoms substitution, transition metal ions doping, and coupling with a narrow band gap semiconductor, etc. This review encompasses several advancements made in these aspects, and also the influence factors such as physical morphologies changing, humidity, as well as the presence of O2 etc, are involved. To be practically considering, TiO2 photocatalysts require being fixed on the bulky supports like silica, alumina, clays and activated carbons. Moreover, photocatalytic coatings deposited on external building materials, like roofing tiles and corrugated sheets, is becoming the attractive application potentials to remove toluene from air.

Fe2O3 nanoparticle mediated molecular growth and soot inception from the oxidative pyrolysis of 1-methylnaphthalene

While it is well documented iron oxide can reduce soot through burnout in the oxidative regions of flames, it may also impact molecular growth and particle inception. The role of Fe2O3 nanoparticles in mass growth of soot from 1-methylnapthalene (1-MN) was studied in a dual-zone, high-temperature flow reactor. An iron substituted, dendrimer template was oxidized in the first zone to generate ~5 nm Fe2O3 nanoparticles, which were seeded into the second zone of the flow reactor containing 1-MN at 1100°C and ϕ = 1.4-5.0. Enhanced molecular growth in the presence of Fe2O3 nanoparticles resulted in increased yields of polycyclic aromatic hydrocarbons (PAH) and soot compared to purely gas-phase reactions of 1-MN at identical fuel-air equivalence ratios. This also resulted in an increase in soot-number concentration and a slight shift to smaller particles with increasing addition (from no addition to 3 mM) of Fe2O3. Introduction of Fe2O3 nanoparticles resulted in the formation of stabilization of environmentally persistent free radicals (EPFRs), including benzyl, phenoxyl, or semiquinone-type radicals as well as carbon-centered radicals, such as cyclopentadienyl or a delocalized electron in a carbon matrix. At the high concentrations in the flow reactor, these resonance-stabilized free radicals can undergo surface-mediated, radical-radical, molecular growth reactions which may contribute to molecular growth and soot particle inception.