The demand for clean fuels is increasing throughout the world, with more stringent environmental regulations for transportation fuels including marine fuels, particularly regarding their sulfur ...content. Moreover, the quality of crude oil and derived petroleum cuts is getting lower while fossil fuels are still in high demand. Heavy oils are characterized by high sulfur content where most sulfur is found in bulky thiophenic structures difficult to remove using conventional high pressure hydrodesulfurization process. However they appeared more reactive in oxidative desulfurization (ODS) process, carried out at mild conditions without hydrogen pressure. This review focuses for the first time on the heavy fuels initially containing more than 0.5 wt.%S and upgraded by the ODS process. Different attractive approaches of the literature towards ODS are reported using homogeneous and heterogeneous catalysis. Recent developments in ODS assisted with ultrasound technology and the use of ionic liquid to enhance ODS efficiency will be fully detailed and discussed to better understand their viability when applied to high sulfur content, high viscosity, and high boiling point feeds.
Carbonate-containing hydroxyapatites with different Ca/P ratios and optionally containing Na+ cations were successfully synthesized using a precipitation method. The solids were extensively ...characterized by XRD, LEIS, XPS, IR, TGA and NMR. Further, their acid-base properties were determined by NH3-TPD, PEA-XPS, CO2-TPD and by pulsed liquid chromatography using benzoic acid as a probe. The so-obtained structural, textural and acid-base properties could be finely correlated to give a clear picture of the system. The acidic properties of hydroxyapatites were attributed to Ca2+, surface HPO42- and OH- vacancies and the basic properties were attributed to PO43-, OH- and CaO species. The fine-tuning of the amount, of the nature and the strength of acid-base properties derived by varying the carbonate content in hydroxyapatites can find applications in catalysis, which was illustrated by isopropanol reactivity.
Nickel salts of Keggin heteropolytungstates with the general formula Ni
(A = Si/P) were synthesized and studied as bulk catalytic materials or supported ones by deposition on modified and ...functionalized clay minerals (pillared layered clay and porous clay heterostructure). Characterizations by Raman,
P and
Si-NMR, and ESEM-EDS techniques showed that pure and supported systems preserved the Ni/W ratio and the expected structural properties of heteropolyanions. These materials were evaluated as catalysts in the selective oxidation of sulfides to sulfoxides or sulfones, using aqueous hydrogen peroxide and mild reaction conditions. The bulk materials, with a higher content of Ni, displayed a remarkable catalytic behavior in the oxidation of diphenyl sulfide (Ni
PW
NiO
H, 90% conversion in 15 min at 75°C, 100% sulfone selectivity in 3 h). Supported catalysts, particularly the non-functionalized PCH (Ni
SW
/PCH), showed excellent activity, with also being selective in the oxidation of sulfide to sulfoxide (87% conversion, 88.9% sulfoxide selectivity). The reuse of these materials was studied in the optimum reaction conditions, resulting in similar activity and selectivity.
Selective oxidation reaction of DPS to DPSO2 with hydrogen peroxide as oxidant in presence of nickel salts of Keggin heteropolytungstates as catalysts
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•Oxidative desulfurization was efficient on marine fuels with S content of 3%.•Sulfides conversion was monitored by GC-SCD.•Applying ultrasounds before reaction was beneficial to ...oxidative desulfurization.•High desulfurization efficiency up to 80 % was achieved on marine fuels.
Oxidative desulfurization (ODS) was applied to three marine fuels with viscosities between 380 and 700 cSt (centistokes) and sulfur contents between 0.79 and 3.27 wt.%, using a MoO3/Al2O3 catalyst. H2O2 was chosen as oxidizing agent with a low oxidant to sulfur ratio of 3, for economic and environmental reasons. Global sulfur removal was obtained after extraction of sulfones by dimethylformamide. Oxidation efficiency was evaluated by monitoring the conversion of alkyl-benzothiophenes and dibenzothiophene molecule by gas chromatography (GC) with a sulfur specific detector. Applying ultrasounds prior to oxidation was found to significantly enhance conversions and sulfur removal, the effect being more pronounced when initial efficiency was low, that is for more refractory molecules and heavier fuels. Ultrasound assisted ODS (UAOD) was effective on raw fuels with initial viscosity below 700 cSt. Indeed, dilution decreased the viscosity of the fuels, allowing reaction to be effective even on initially very heavy fuels. The presence of asphaltenes dissolved or precipitated in the feed did not affect the conversion of Cx-BTs and DBT significantly, with only slight variations of global sulfur removal rates. Global desulfurization rates between 60 and 80 % were obtained, clearly showing the efficiency of UAOD applied to complex matrices such as marine fuels.
Catalytic oxidative desulfurization (ODS) of fuel oil has received much attention. For this, the synthesis of a highly efficient ODS catalyst has been strongly pursued. Polyoxometalates (POMs) as ...active centers have been studied for ODS reactions. However, generally the obtained POM catalysts exhibited ordinary catalytic ODS performance mainly due to the role of single active sites. Moreover, the synthesis needs to be completed with the addition of solvent. In this work, we report a new approach to prepare highly efficient ODS catalysts with POM sites. This process can be simply realized by the combination of a common POM (H
3
PW
12
O
40
) and a stable metal-organic framework (MOF) material UiO-66(Zr) without the addition of solvent. More importantly, it is found that polyoxometalate encapsulated in UiO-66(Zr) possesses hierarchical porosity and double active sites. As a result, the catalyst exhibited extraordinary catalytic activity by using H
2
O
2
as an oxidant in the ODS reactions of benzothiophene, dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene. The turnover frequency (TOF) for the removal of DBT reached 293 h
−1
at room temperature, which is much higher than that of the reported catalysts. Such outstanding catalytic performance could be mainly attributed to easy accessibility of active sites and the existence of two types of active centers in polyoxometalate species and defective UiO-66(Zr).
POM/UiO-66(Zr) with hierarchical porosity and double active sites was synthesized by a solvent-free method for oxidation desulfurization of fuel oil.
Deep desulfurization of fuel oil has received much attention due to the stringent demand of environmental regulations. In this work, we report that titanium terephthalate based materials with ...hierarchical porosity have been successfully synthesized for deep oxidative desulfurization of fuel oil. The catalytic results indicated that hierarchical porous titanium terephthalate based materials displayed superior catalytic performance in the ODS reactions of benzothiophene, dibenzothiophene and 4,6-dimethyldibenzothiophene. Additionally, this type of catalyst is also of great potential in other oxidative reactions involving the oxidation of phenethyl alcohol or cyclohexene. Such outstanding catalytic performance could be attributed to the presence of highly active sites and rich mesoporosity in hierarchical porous titanium terephthalate based materials.
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•Hierarchical porous titanium terephthalate based materials have been synthesized.•Relatively high synthetic temperature is beneficial for producing the materials with rich mesoporosity.•Ti-BDC-180 displayed superior catalytic performance in oxidation reactions.•Ti-BDC-180 is a heterogeneous catalyst and can be reused.
During the preparation, the nature of the precipitating agent strongly influences the synthesis of magnesium phosphate. Ortho and pyrophosphate can be obtained with the use of NaOH and NH
4OH, ...respectively. The solids obtained were investigated as synthesized or after calcination by various physico-chemical techniques such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential thermal analysis (DTA). The compounds calcined at 773
K have been further characterized by
31P MAS-NMR spectroscopy.
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