Environmental concerns have driven the need to remove sulfur-containing compounds from light oil. As the oxidative desulfurization is conducted under very mild reaction conditions, much attention has been recently devoted to this process. In this contribution, the developments in selective removal of organosulfur compounds present in liquid fuels via oxidative desulfurization, including both the chemical oxidation and biodesulfurization, are reviewed. At the end of each section, a brief account of the research directions needed in this field is also included.

This paper describes the oxidation of several model S-containing molecules with hydrogen peroxide in L-L phase system using a heterogeneous catalyst under atmospheric pressure in the 333-353 K temperature range. Molybdenum and tungsten compounds are prepared by anion exchange with alkylammonium derivatives covalently anchored to silica gel. These solids are robust heterogeneous catalysts able to activate selectively hydrogen peroxide to remove sulfur compounds via oxidation (ODS). The influence of several reaction variables (the support, the reaction temperature, the nature of the substrate, the solvent, the molar ratio of the oxidant (H 2 O 2), the S-containing molecule, the catalysts nature and the reuse of the catalysts) on the performance was examined. The potential of this methodology is illustrated by the complete S-removal from a 0.2 wt% dibenzothiophene mixture at 353 K in less than 1 h of reaction. Molybdenum catalysts exposed to hydrogen peroxide form peroxomolybdates moieties which are more active than acid precursors. The activated Mo catalysts are very active in ODS reaction and can be reused four times without lose of activity.

We report a study of the epoxidation of soybean oil and soybean methyl esters with hydrogen peroxide in dilute solution (6 wt%) using an amorphous heterogeneous Ti/SiO 2 catalyst in the presence of tert-butyl alcohol. The influence of some relevant process variables such as temperature and the hydrogen peroxide-to-double bond molar ratio on performance is examined. The highest yields of epoxidized olefins were obtained upon using a H 2 O 2 : substrate molar ratio of 1.1 : 1. Higher ratios than this were not effective for speeding up the reaction. Under the experimental conditions employed in this work, no degradation of the oxirane ring was observed.

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Titanium/silica systems were prepared by grafting a titanium alkoxide (titanium isopropoxide and titanium (triethanolaminate) isopropoxide) precursor onto amorphous silica. The grafting process, which consisted of the hydrolysis of the Ti precursor by the hydroxyl groups on the silica surface, yielded samples containing Ti-loadings of 1-1.6 wt %. The as synthesized and calcined TiO(2)-SiO(2) samples were characterized by UV-vis, FTIR, XPS, and XANES spectroscopic techniques. These systems were tested in the liquid-phase epoxidation of oct-1-ene with hydrogen peroxide reaction. Spectroscopic data indicated that titanium anchoring takes place by reaction between the alkoxide precursor and surface OH groups of the silica substrate. The nature of surface titanium species generated by chemical grafting depends largely on the titanium precursor employed. Thus, the titanium isopropoxide precursor yields tetrahedrally coordinated polymeric titanium species, which give rise to a low-efficiency catalyst. However, if an atrane precursor (titanium (triethanolaminate) isopropoxide) is employed, isolated titanium species are obtained. The fact that these species remain isolated even after calcination is due to the protective effect of the triethanolaminate ligand that avoids titanium polymerization. These differences in the titanium environment have a pivotal role in the performance of these systems in the epoxidation of alkenes with hydrogen peroxide.

Efficient removal of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyl dibenzothiophene (DMDBT) has been successfully achieved via oxidation with hydrogen peroxide in liquid phase using an amorphous silica-loaded titanium oxide catalyst. Both BT and DBT are easily oxidized to the corresponding sulfones, however in the case of DMDBT the steric hindrance of the alkyl groups makes the approach of the S-atom to the catalyst active centre (an isolated Ti(IV) species) difficult and therefore its reactivity is inhibited. The concentration of the organosulfur compound, the H 2 O 2 concentration and the nature of the solvent play a key role in the rate of S-removal.

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A good correlation between the experimental UV-Vis spectra of titanium containing catalysts and the photo-physical properties calculated using Time-Dependent Density Functional Theory (TD-DFT) has been found. This finding makes the TD-DFT methodology an excellent tool to generate and interpret the electronic spectra of isolated atoms in the surface of heteroatomcontaining inorganic substrates.