Efficient oxidation of sulfides catalyzed by a temperature-responsive phase transfer catalyst [(C18H37)2(CH3)2N]7 PW11O39 with hydrogen peroxide

Solvent-Free Desulfurization System to Produce Low-Sulfur Diesel Using Hybrid Monovacant Keggin-Type Catalyst

Two quaternary ammonium catalysts based on the monovacant polyoxotungstate ([PW₁₁O₃₉]⁷⁻, abbreviated as PW₁₁) were prepared and characterized. The desulfurization performances of the PW₁₁-based hybrids (of tetrabutylammonium and trimethyloctadecylammonium, abbreviated as TBA[PW₁₁] and ODA[PW₁₁], respectively), the corresponding potassium salt (K₇PW₁₁O₃₉, abbreviated as KPW₁₁) and the peroxo-compound (TBA-PO₄[WO(O₂)₂], abbreviated as TBA[PW₄]) were compared as catalysts for the oxidative desulfurization of a multicomponent model diesel (2000 ppm S). The oxidative desulfurization studies (ODS) were performed using solvent-free systems and aqueous H₂O₂ as oxidant. The nature of the cation in the PW₁₁ catalyst showed to have an important influence on the catalytic performance. In fact, the PW₁₁-hybrid catalysts showed higher catalytic efficiency than the peroxo-compound TBA[PW₄], known as Venturello compound. TBA[PW₁₁] revealed a remarkable desulfurization performance with 96.5% of sulfur compounds removed in the first 130 min. The reusability and stability of the catalyst were also investigated for ten consecutive ODS cycles without loss of activity. A treated clean diesel could be recovered without sulfur compounds by performing a final liquid/liquid extraction diesel/EtOH:H₂O mixture (1:1) after the catalytic oxidative step.

Improving the Catalytic Performance of Keggin [PW12O40]3- for Oxidative Desulfurization: Ionic Liquids versus SBA-15 Composite

Different methodologies were used to increase the oxidative desulfurization efficiency of the Keggin phosphotungstate [PW₁₂O₄₀]^3- (PW₁₂). One possibility was to replace the acid proton by three different ionic liquid cations, forming the novel hybrid polyoxometalates: [BMIM]₃PW₁₂ (BMIM as 1-butyl-3-methylimidazolium), [BPy]₃PW₁₂ (BPy as 1-butylpyridinium) and [HDPy]₃PW₁₂ (HDPy as hexadecylpyridinium. These hybrid Keggin compounds showed high oxidative desulfurization efficiency in the presence of [BMIM]PF₆ solvent, achieving complete desulfurization of multicomponent model diesel (2000 ppm of S) after only 1 h, using a low excess of oxidant (H₂O₂/S = 8) at 70 °C. However, their stability and activity showed some weakness in continuous reused oxidative desulfurization cycles. An improvement of stability in continuous reused cycles was reached by the immobilization of the Keggin polyanion in a strategic positively-charged functionalized-SBA-15 support. The PW₁₂@TM⁻SBA-15 composite (TM is the trimethylammonium functional group) presented similar oxidative desulfurization efficiency to the homogeneous IL⁻PW₁₂ compounds, having the advantage of a high recycling capability in continuous cycles, increasing its activity from the first to the consecutive cycles. Therefore, the oxidative desulfurization system catalyzed by the Keggin-type composite has high performance under sustainable operational conditions, avoids waste production during recycling and allows catalyst recovery.

Sandwich type polyoxometalates encapsulated into the mesoporous material: synthesis, characterization and catalytic application in the selective oxidation of sulfides

The A-type sandwich polyoxometalates of [(HOSn^IVOH)₃(PW₉O₃₄)₂]¹²⁻ (P₂W₁₈Sn₃) and [(OCe^IVO)₃(PW₉O₃₄)₂]¹²⁻ (P₂W₁₈Ce₃) were immobilized for the first time into the porous metal–organic framework MIL-101(Cr). FT-IR, powder X-ray diffraction, SEM-EDX, ICP analysis, N₂ adsorption and thermogravimetric analysis collectively confirmed immobilization and good distribution of polyoxometalates into cages of MIL-101(Cr). The catalytic activities of the homogeneous P₂W₁₈Sn₃ and P₂W₁₈Ce₃ and the corresponding heterogeneous catalysts were examined in the oxidation of sulfides to sulfones with H₂O₂ as the oxidant at room temperature. The effects of different dosages of polyoxometalates, type of solvent, reaction time, amount of catalyst and oxidant in this catalytic system were investigated. The new P₂W₁₈Sn₃@MIL-101 and P₂W₁₈Ce₃@MIL-101 nanocomposites exhibited good recyclability and reusability in at least five consecutive reaction cycles without significant loss of activity or selectivity.

The A-type sandwich POMs of [(HOSn^IVOH)₃(PW₉O₃₄)₂]^12– (P₂W₁₈Sn₃) and [(OCe^IVO)₃(PW₉O₃₄)₂]^12– (P₂W₁₈Ce₃) were immobilized for the first time into the porous MIL-101 MOF. Their catalytic activities were examined in the oxidation of sulfides to sulfones at room temperature.

Green catalysis for the selective oxidation of sulfides with high turnover numbers in water at room temperature

A hybrid catalyst based on monoprotonated divanadium-substituted phosphotungstate ([γ-HPV₂W₁₀O₄₀]⁴⁻) was synthesized and used for the selective oxidation of sulfides.

Facile synthesis and characterization of Fe3O4@MgAl-LDH@STPOM nanocomposites for highly enhanced and selective degradation of methylene blue

A novel layered and cauliflower-like Fe₃O₄@MgAl-LDH@Ce₃W₁₈ nanocomposite has been synthesized by the selective ion-exchange method.

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.

Selective sulfoxidation with hydrogen peroxide catalysed by a titanium catalyst

A cyclopentadienyl–silsesquioxane titanium complex efficiently catalyses the selective oxidation of sulfides to sulfoxides (85–98% yield in 5 min at ambient temperature) and sulfones with near-stochiometric amount of aqueous H₂O₂ in methanol.

Novel polyoxometalate silica nano-sized spheres: efficient catalysts for olefin oxidation and the deep desulfurization process

A novel method to prepare silica nano-sized particles incorporating polyoxometalates was developed leading to a new efficient heterogeneous oxidative catalyst.