Suhang Xun

One-pot extraction combined with metal-free photochemical aerobic oxidative desulfurization in deep eutectic solvent

Five low-cost deep eutectic solvents (DESs) were synthesized based on choline chloride (ChCl) and a series of straight-chain monobasic acids. Under UV light irradiation, one-pot extraction combined with the metal-free photochemical aerobic oxidative deep desulfurization of fuels in deep eutectic solvents was successfully achieved. This liquid-liquid extraction and photochemical oxidative desulfurization system (EPODS) comprised of air, isobutylaldehyde (IBA), DESs and model oil. The factors influencing sulfur removal were systematically investigated, including the amount of DES, volume ratio of model oil and IBA, different sulfur concentrations, different substrates and fuel composition. The sulfur removal of dibenzothiphene (DBT) could reach 98.6% with air as oxidizing agent under UV light irradiation. Sulfur removal by different sulfur compounds decreased as BT > DBT > 4,6-DMDBT. The possible photochemical oxidative desulfurization mechanism was researched by gas chromatograph-mass spectrometer (GC-MS), electron spin-resonance (ESR) spectroscopy and density functional theory (DFT).

Few-layered graphene-like boron nitride induced a remarkable adsorption capacity for dibenzothiophene in fuels

Metal-free graphene-like boron nitride (BN) samples were prepared and applied as adsorbents for removing dibenzothiophene (DBT) in model oil. The results showed that the graphene-like BN exhibited a remarkable adsorption performance. The adsorption capacity could reach 28.17 mg S g−1 adsorbent. Experiments have been carried out to investigate the effects of the number of BN layers, DBT initial concentration, and temperature on DBT adsorption. Langmuir and Freundlich isotherm models were used to study the adsorption of DBT on BN. The kinetic results showed that the adsorption process was best described by the pseudo-second-order kinetic model. Density functional theory (DFT) was employed to prove that the Lewis acid–base interaction plays an important role in removing DBT over graphene-like BN.

Carbon-doped porous boron nitride: metal-free adsorbents for sulfur removal from fuels

Novel carbon-doped porous boron nitride (C-BN) has been successfully prepared by using 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) as a soft template and the carbon source via calcination under N2 atmosphere. Multiple techniques were applied to investigate the structure, morphology, and adsorptive desulfurization performance. The metal-free porous C-BN displayed enhanced adsorption performance for dibenzothiophene (DBT) than pure BN materials and exhibited one of the highest adsorption capacities reported up to now (49.75 mg S g−1 adsorbent according to the Langmuir isotherm model, 35.2 mg S g−1 adsorbent for 500 ppm sulfur model oil). After three times recycling, the adsorption capacity slightly decreased from 35.2 to 27.2 mg S g−1 adsorbent. The excellent adsorption performance of porous C-BN was attributed to the more exposed atoms along the edges of the pores and the stronger Lewis acid–base interactions between DBT and carbon-doped porous BN. Moreover, it is believed that this strategy to control the structure and composition of BN can be extended to incorporate other heteroatoms and control the pore size for BN materials by changing the anion or cation of the ionic liquids.

Supported ionic liquid [Bmim]FeCl4/Am TiO2 as an efficient catalyst for the catalytic oxidative desulfurization of fuels

High activity oxidation of sulfur compounds to sulfones in extraction coupled with catalytic oxidative desulfurization (ECODS) system catalyzed by supported ionic liquid [Bmim]FeCl4/Am TiO2 was reported. The catalysts were analyzed by thermogravimetric (TG) analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). It was found that [Bmim]FeCl4 and Am TiO2 had a synergistic effect on the desulfurization system. Effects of calcination temperature of the catalyst and various reaction conditions on the catalytic activity of desulfurization were investigated. Moreover, GC-MS analyses were employed to prove the process of the desulfurization. As a solid catalyst, the supported ionic liquid could be separated from the reaction easily. The recycling tests showed that the desulfurization efficiency remained 100% after reusing it for 25 times. Therefore, the ECODS system has excellent reusability and is promising for industrial applications for catalytic oxidative desulfurization.

Deep oxidative desulfurization of fuels catalyzed by magnetic Fenton-like hybrid catalysts in ionic liquids

Three magnetic Fenton-like hybrid materials Q[FeCl4] [Q = (CH3)4N, C14H29N(CH3)3, and C18H37N(CH3)3] were synthesized and characterized, which were used as catalysts in oxidative desulfurization combining ionic liquids (ILs) extraction and H2O2 oxidation. The reaction conditions were optimized by investigating reaction temperature, time, the type of ILs, the amount of H2O2 and catalysts in detail. The removal of dibenzothiophene (DBT) in model oil could get up to 97.0% at 30 °C for 1 h. In addition, the utilization rate of H2O2 could be improved by adding it in batches. The catalytic system, consisting of IL and catalysts, could be easily separated by applying an external magnetic field and regeneration by washing with water, which could be recycled six times with a slight decrease in desulfurization efficiencies.

Synthesis of mesoporous WO3/TiO2 catalyst and its excellent catalytic performance for the oxidation of dibenzothiophene

A series of WO3/TiO2 catalysts with a pore structure were successfully synthesized. The catalysts were systematically characterized and it was found that different calcination temperatures had great effects on the pore structure of the catalysts. The catalyst presented a mesoporous structure after calcining at 550 °C (expressed as 550-WO3/TiO2) and had the largest specific surface area among the mesoporous catalysts. The oxidation of dibenzothiophene (DBT) with 550-WO3/TiO2 catalyst reached 100% under optimum conditions. After recycling for 6 times, the oxidation of DBT could still achieve a DBT removal of 96.7%, suggesting that the catalyst had good stability and recycle performance. In addition, DBT sulfone (DBTO2) was proven to be the only oxidation product of DBT after the reaction, as observed by the GC-MS analysis. The catalytic activities of the catalyst on different substrates were also investigated, and the activities decreased in the order: DBT > 4-MDBT > 4,6-DMDBT > BT.

TiO2 microspheres supported polyoxometalate-based ionic liquids induced catalytic oxidative deep-desulfurization

A series of TiO2 microspheres supported polyoxometalate-based ionic liquids (POM-ILs) with different tungsten–titanium molar ratios and different carbon chains ILs were successfully prepared. The supported catalysts were characterized by TG, FT-IR, Raman, Nitrogen adsorption–desorption isotherms, XPS and SEM. It is confirmed that the POM-ILs were indeed immobilized on TiO2 microspheres and the structures were maintained. The appropriate morphology and loading of the supported catalyst was obtained with [C16mim]4SiW12O40 (C16SiW) IL and the tungsten–titanium molar ratio was 0.1 (0.1-C16SiW–TiO2). This heterogeneous catalyst strategy makes the usage of ionic liquid decrease sharply. The supported catalyst 0.1-C16SiW–TiO2 exhibited high catalytic activity in the extractive coupled catalytic oxidative desulfurization (ECODS) system under mild conditions. The removal of dibenzothiophene (DBT) reached 95.3% with low-dosage oxidant (the molar ratio of H2O2 and DBT is only 2), which means high efficiency utilization of H2O2 was achieved in this system. Moreover, DBT could be removed completely with a little excess oxidant. Furthermore, the 0.1-C16SiW–TiO2 catalyst showed excellent reusing ability, the desulfurization efficiency had no obvious decrease after recycling for 8 times, which made it a promising catalyst in oxidative desulfurization process.

Fabrication and characterization of tungsten-containing mesoporous silica for heterogeneous oxidative desulfurization

A series of functional, tungsten-containing mesoporous silica materials (W-SiO 2 ) have been fabricated directly from an ionic liquid that contained imidazole and polyoxometalate, which acted as mesoporous template and metal source respectively. These materials were then characterized through X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectra (FTIR), diffuse reflectance spectra (DRS), and N 2 adsorption-desorption, which were found to contain tungsten species that were effectively dispersed throughout the structure. The as-prepared materials W-SiO 2 were also found to possess a mesoporous structure. The pore diameters of the respective sample W-SiO 2 -20 determined from the TEM images ranged from 2 to 4 nm, which was close to the average pore size determined from the nitrogen desorption isotherm (2.9 nm). The materials were evaluated as catalysts for the heterogeneous oxidative desulfurization of dibenzothiophene (DBT), which is able to achieve deep desulfurization within 40 min under the optimal conditions (Catalyst (W-SiO 2 -20) = 0.01 g, temperature = 60 ℃, oxidant (H 2 O 2 ) = 20 μL). For the removal of different organic sulfur compounds within oil, the ability of the catalyst (W-SiO 2 -20) under the same conditions to remove sulfur compounds decreased in the order: 4,6-dimethyldibenzothiophene ＞ Dibenzothiophene ＞ Benzothiophene ＞ 1-dodecanethiol. Additionally, they did not require organic solvents as an extractant in the heterogeneous oxidative desulfurization process. After seven separate catalytic cycles, the desulfurization efficiency was still as high as 90.3%. From the gas chromatography-mass spectrometer analysis, DBT was entirely oxidized to its corresponding sulfone DBTO 2 after reaction. A mechanism for the heterogeneous desulfurization reaction was proposed.

Magnetic mesoporous nanospheres supported phosphomolybdate-based ionic liquid for aerobic oxidative desulfurization of fuel

Phosphomolybdate-based ionic liquid [(C8H17)3NCH3]3PMo12O40 was prepared and supported on a magnetic mesoporous silica (γ-Fe2O3@SiO2@mSiO2) to obtain a magnetic mesoporous catalyst. The morphology and components of the catalyst were characterized by FT-IR, XRD, XPS, SEM, TEM, nitrogen adsorption-desorption isotherms, and VSM. With air as oxidant, the catalyst showed perfect desulfurization performance in oxidation of dibenzothiophene (DBT). The removal of DBT from model oil could reach 100% within 5 h at 120 °C. After reaction, the catalyst could be separated by a magnet and recycled at least four times without obvious decrease in the catalytic performance.

Amorphous TiO2-supported Keggin-type ionic liquid catalyst catalytic oxidation of dibenzothiophene in diesel

Supported ionic liquid (IL) catalysts [Cnmim]3PMo12O40/Am TiO2 (amorphous TiO2) were synthesized through a one-step method for extraction coupled catalytic oxidative desulfurization (ECODS) system. Characterizations such as FTIR, DRS, wide-angle XRD, N2 adsorption–desorption and XPS were applied to analyze the morphology and Keggin structure of the catalysts. In ECODS with hydrogen peroxide as the oxidant, it was found that ILs with longer alkyl chains in the cationic moiety had a better effect on the removal of dibenzothiophene. The desulfurization could reach 100% under optimal conditions, and GC–MS analysis was employed to detect the oxidized product after the reaction. Factors affecting the desulfurization efficiencies were discussed, and a possible mechanism was proposed. In addition, cyclic experiments were also conducted to investigate the recyclability of the supported catalyst. The catalytic activity of [C16mim]3PMo12O40/Am TiO2 only dropped from 100% to 92.9% after ten cycles, demonstrating the good recycling performance of the catalyst and its potential industrial application.