Oxidation of Aromatic Sulfur Compounds Catalyzed by Organic Hexacyanoferrates in Ionic Liquids with a Low Concentration of H₂O₂ as an Oxidant

A series of organic hexacyanoferrates were synthesized and employed as catalysts in ionic liquids (ILs) for catalytic oxidation of dibenzothiophene (DBT), benzothiophene (BT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT). High activity was achieved using 1-butyl-3-methylimidazolium hexacyanoferrate ([C₄mim]₃Fe­(CN)₆) as a catalyst and 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄mim]­BF₄) as an extractant in the presence of H₂O₂ under mild conditions. It was interesting to find that the concentration of H₂O₂ had a significant influence on desulfurization efficiency. The sulfur removal was 76.3% with 30 wt % H₂O₂ as an oxidant, while it could reach 97.9% with 7.5 wt % H₂O₂. Electron spin resonance (ESR) spectroscopy measurements gave the evidence that the active oxygen species O₂^• ^– was generated in the catalytic oxidative desulfurization process, and gas chromatography–mass spectrometry (GC–MS) analysis indicated that the sulfur compounds were oxidized to the corresponding sulfones. The influence factors, such as reaction temperature, time, concentration, and dosage of H₂O₂, amount of catalyst, catalytic system recycling, and different sulfur-containing compounds, were investigated. The kinetic investigations showed that oxidation of sulfur compounds presented a pseudo-first-order kinetic. Under the optimal conditions, the catalytic system could be recycled at least 4 times without a remarkable decrease in activity

A Novel Reaction-Controlled Foam-Type Polyoxometalate Catalyst for Deep Oxidative Desulfurization of Fuels

A novel reaction-controlled foam-type catalyst has been designed by pairing 1-hexadecyl-3-methyl-imidazolium cation with peroxomolybdate anion. This catalyst switched from the powder to the foam-type active species, exhibiting high catalytic activity in the oxidative desulfurization process. After the reaction was finished, the foam became brittle and returned to powder form, which could be easily separated and reused. Reasons for this change were detailed by experiments. The removal of dibenzothiophene (DBT) could reach 98.4% under the optimal conditions of <i>n</i>(DBT)/<i>n</i>(catalyst)/<i>n</i>(H₂O₂) = 30:1:180, at 50 °C for 1 h. The catalyst could be recycled six times, and the sulfur removal still remained to be about 93.9%

Graphene-Analogue Hexagonal BN Supported with Tungsten-based Ionic Liquid for Oxidative Desulfurization of Fuels

Graphene-analogue hexagonal boron nitride (G-<i>h</i>-BN), as a novel few-layer material, was prepared and used as a support to coat with tungsten-based ionic liquid (IL) in oxidative desulfurization. Designed G-<i>h</i>-BN supported with tungsten-based IL (IL/G-<i>h</i>-BN) heterogeneous catalyst was characterized by atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy. This few-layer material supported with IL strategy makes the usage amount of IL reduce remarkably, which not only presents excellent catalytic activity but also is superior to homogeneous catalysts of ILs themselves. Additionally, compared with the multilayer hexagonal boron nitrides (M-<i>h</i>-BN) or commercial bulk BN supported with IL, the IL/G-<i>h</i>-BN catalyst exhibited better catalytic activity in oxidation of dibenzothiophene, reaching 99.3% sulfur removal. The adsorption and catalytic oxidative desulfurization mechanism was further studied by gas chromatography–mass spectrometry, Fourier transform infrared spectroscopy, X-ray diffraction and UV-diffuse reflectance spectroscopy. Moreover, the IL/G-<i>h</i>-BN catalyst could be recycled five times with little decrease in catalytic activity

Phosphotungstic Acid Immobilized on Ionic Liquid-Modified SBA-15: Efficient Hydrophobic Heterogeneous Catalyst for Oxidative Desulfurization in Fuel

A heterogeneous catalyst system was synthesized by immobilizing phosphotungstic acid on ionic liquid-modified mesoporous silica SBA-15 and applied in oxidative desulfurization. Structure and properties of catalyst were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the contact angle. The results demonstrated that the synthesized catalyst possessed ordered mesopore structure and high special surface area. Due to the introduction of imidazole-based ionic liquid, the catalyst exhibited good wettability for model oil, which had significant contribution to desulfurization activity. Both DBT and 4,6-DMDBT could be removed completely at mild conditions (60 °C, 40 min). The removal of BT also can reach 81.3% within 60 min. Furthermore, the catalyst was recovered and reused in four reaction runs with a slight decrease in activity

Silver Nanoparticle-Decorated Boron Nitride with Tunable Electronic Properties for Enhancement of Adsorption Performance

In this paper, a series of silver nanoparticle (AgNP)-decorated boron nitride (Ag-BN) with different Ag amounts were successfully synthesized by a one-pot pyrolysis method and used as novel high-efficiency adsorbents for the removal of organic pollutant tetracycline (TC) and rhodamine B (RhB). According to the adsorption capacity of the samples, the obtained optimal Ag/B molar ratio was 1%. The adsorption data fitted well with the pseudo-second-order kinetics and Langmuir isotherm models with the maximum adsorption capacity of 358 and 880 mg/g for TC and RhB, respectively. The thermodynamic studies suggested that the adsorption process was spontaneous and endothermic in nature. The introduction of AgNP onto BN enhanced the adsorption capacity on account of tunable electronic properties. The adsorption mechanism is discussed in detail with the effect of pH, density function theory (DFT), and thermodynamics