Keggin-structured polyoxometalate-based ionic liquid salts: Thermoregulated catalysts for rapid oxidation of sulfur-based compounds using H2O2 and extractive oxidation desulfurization of sulfur-containing model oil

Recent Advances in Catalytic Oxidation of Organic Sulfides: Applications of Metal–Ionic Liquid Catalytic Systems

Catalytic oxidation of organic sulfides is of considerable significance in industrial chemistry and fuel industry. Therefore, numerous methods have been developed for the oxidation. Metal-containing ionic liquid-based catalysts can catalyze the selective oxidation reactions and are highly used in chemical processes, which have also been used as effective solvents, reaction media, extractants, and catalysts for the oxidation of organic sulfides including oxidative desulfurization of fuel oil. Recently, much attention is being drawn to the preparation of heterogenous catalysts based on the immobilization of metal- or nonmetal-containing ILs on diverse solid supports, which can be easily separated after the completion reaction and recycled. Therefore, there is still an increasing interest in developing new and efficient catalytic procedures for the oxidation of organic sulfides. In this review, we have outlined the recent advances in catalytic oxidation of organic sulfides including oxidative desulfurization of fuel oil. The versatilities and adaptabilities of metal–ionic liquid catalytic systems in the selective oxidation of sulfides are considered a powerful research field in these transformations.

Polyoxometalate Dicationic Ionic Liquids as Catalyst for Extractive Coupled Catalytic Oxidative Desulfurization

Wettability is an important factor affecting the performance of catalytic oxidative desulfurization. In order to develop an efficient catalyst for the extractive coupled catalytic oxidative desulfurization (ECODS) of fuel oil by H2O2 and acetonitrile, a novel family of imidazole-based polyoxometalate dicationic ionic liquids (POM-DILs) [Cn(MIM)2]PW12O40 (n = 2, 4, 6) was synthesized by modifying phosphotungstic acid (H3PW12O40) with double imidazole ionic liquid. These kinds of catalysts have good dispersity in oil phase and H2O2, which is conducive to the deep desulfurization of fuel oil. The catalytic performance of the catalysts was studied under different conditions by removing aromatic sulfur compound dibenzothiophene (DBT) from model oil. Results showed that [C2(MIM)2]PW12O40 had excellent desulfurization efficiency, and more than 98% of DBT was removed under optimum conditions. In addition, it also exhibited good recyclability, and activity with no significant decline after seven reaction cycles. Meanwhile, dibenzothiophene sulfone (DBTO2), the only oxidation product of DBT, was confirmed by Gas Chromatography-Mass Spectrometry (GC-MS), and a possible mechanism of the ECODS process was proposed.

Metal-Based Ionic Liquids in Oxidative Desulfurization: A Critical Review

Ionic liquids (ILs) as novel functional desulfurization materials have attracted increasing attentions. Metal-based ionic liquids (MILs) are classified into three types of metal chloride ILs, metal oxide ILs, and metal complex ILs based on the definition and basic structure of MILs in this critical review. On the basis of the properties of ILs such as structure designability, super dissolution performance, good thermal and chemical stability, nonflammability, and wide electrochemical window, MILs exhibit unique advantages on hydrophobicity, oxidation performance, and Brönsted-Lewis acidity. Therefore, MILs possess both the absorption and oxidation centers for the intramolecular adsorption and oxidation to improve the oxidative desulfurization (ODS) process. During the novel nonaqueous wet oxidative desulfurization process (Nasil), H₂S can be oxidized into elemental sulfur with hydrophobic MILs, which can be regenerated by oxygen for recycle, to solve the problems of low sulfur capacity, low sulfur quality, and severe secondary pollution in the aqueous Lo-Cat wet oxidative desulfurization process. Another outstanding feature of MILs in ODS is biomimetic catalysis, which has the function of activating molecular oxygen and improving the oxidation performance. Metal oxide ILs and metal complex ILs are used in combination with hydrogen peroxide or oxygen with the existing water to generate a Fenton-like reaction to convert hydrophobic organic sulfur or SO₂ into hydrophilic sulfoxide/sulfone or sulfur acid, respectively. However, the corrosion of Cl^- to the equipment and emulsification phenomenon in the extraction process of sulfoxide/sulfone separation still need further study. Furthermore, the promising strategies to construct highly efficient and green desulfurization processes for large-scale applications are provided.

Electrochemical investigation and amperometry determination iodate based on ionic liquid/polyoxotungstate/P-doped electrochemically reduced graphene oxide multi-component nanocomposite modified glassy carbon electrode

A novel modified glassy carbon electrode (GCE) was successfully fabricated with a tetra-component nanocomposite consisting of (1,1′-(1,4-butanediyl)dipyridinium) ionic liquid (bdpy), SiW₁₁O₃₉Ni(H₂O) (SiW₁₁Ni) Keggin-type polyoxometalate (POM), and phosphorus-doped electrochemically reduced graphene oxide (P-ERGO) by electrodeposition technique. The (bdpy)SiW₁₁Ni/GO hybrid nanocomposite was synthesized by a one-pot hydrothermal method and characterized by UV-vis absorption, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, thermogravimetric-differential thermal analysis (TGA/DTA), and transmission electron microscopy (TEM). The morphology, electrochemical performance, and electrocatalysis activity of the nanocomposite modified glassy carbon electrode ((bdpy)SiW₁₁Ni/P-ERGO/GCE) were analyzed by field emission scanning electron microscopy (FE-SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), cyclic voltammetry (CV), square wave voltammetry (SWV), and amperometry, respectively. Under the optimum experimental conditions, the as-prepared sensor showed high sensitivity of 28.1 μA mM⁻¹ and good selectivity for iodate (IO₃⁻) reduction, enabling the detection of IO₃⁻ within a linear range of 10–1600 μmol L⁻¹ (R² = 0.9999) with a limit of detection (LOD) of 0.47 nmol L⁻¹ (S/N = 3). The proposed electrochemical sensor exhibited good reproducibility, and repeatability, high stability, and excellent anti-interference ability, as well as analytical performance in mineral water, tap water, and commercial edible iodized salt which might provide a capable platform for the determination of IO₃⁻.

Constructing a sensitive electrochemical sensor based on (bdpy)SiW₁₁Ni/P-ERGO/GCE for IO₃⁻ detection at the nanomolar level with noticeable selectivity.

Halloysite nanotubes based heterogeneous solid acid catalysts

Taking into account the excellent catalytic performance of halloysite nanotubes, the main focus of this review article is to unveil the research on halloysite nanotubes for the preparation of solid acids and their applications in acid catalysis.

Polyoxometalate as an effective catalyst for the oxidative desulfurization of liquid fuels: a critical review

In order to meet the stringent environmental and industrial legislation on fuel specifications, sulfur compounds have to be removed efficiently from fuels. The requirement to produce ultralow-sulfur fuels (S < 10 ppm) has stimulated many works in the area of conventional hydro-desulfurization (HDS) method. Oxidative desulfurization (ODS), as an alternative or complementary technology to HDS for deep desulfurization, is conducted with high selectivity and reactivity to sterically hindered S compounds under mild reaction conditions. In the ODS process, using an appropriate oxidant in the presence of a catalyst, organic sulfur compounds can be oxidized selectively to their corresponding sulfoxides and sulfones, which can be easily removed by different separation methods. Having great catalytic characteristics, polyoxometalate materials have been utilized as a vital class of catalysts for deep desulfurization of fuels. In the past few decades, ODS of fuels using polyoxometalate as catalyst has drawn much attention, and various studies have been carried out in this area. Here, we give a critical review for the removal of sulfur compounds from liquid fuels (mostly from diesel and model fuels) by ODS via homogeneous and heterogeneous polyoxometalate catalysts.

Efficient and selective oxidation of sulfides in batch and continuous flow using styrene-based polymer immobilised ionic liquid phase supported peroxotungstates

Good conversion and high selectivity for sulfoxidation have been achieved under segmented and continuous flow using a polystyrene-based polymer immobilised ionic liquid phase (PIILP) peroxotungstate.

A Mn(iii) polyoxotungstate in the oxidation of organosulfur compounds by H2O2 at room temperature: an environmentally safe catalytic approach

A manganese monosubstituted Keggin-type polyoxometalate was used as a catalyst in the oxidation of recalcitrant organosulfur compounds by hydrogen peroxide at room temperature.

A multicomponent assembly approach for the design of deep desulfurization heterogeneous catalysts

An assembly approach has been employed for the preparation of a multi-component heterogeneous catalyst showing high efficiency in deep desulfurization processes.

Experimental study on deep desulfurization of MTBE by electrochemical oxidation and distillation

With the increasing awareness of environmental protection, deep desulfurization of methyl tert-butyl ether (MTBE), which is the most important octane booster in gasoline, is extremely urgent.

Heterogenization of heteropoly compounds: a review of their structure and synthesis

The heterogenization of different types of heteropoly compoundsviasix popular methods from those published over the past recent 15 years is reviewed.