Search Results (77)

This review surveys recent advances and emerging prospects in phase-transfer catalysis (PTC) for fuel desulfurization. In response to increasingly stringent environmental regulations, the removal of sulfur from transportation fuels has become imperative for curbing SO_x emissions. Conventional hydrodesulfurization (HDS) operates under severe temperature–pressure conditions and displays limited efficacy toward sterically hindered thiophenic compounds, motivating the exploration of non-hydrogen routes such as oxidative desulfurization (ODS). Within ODS, PTC offers distinctive benefits by shuttling reactants across immiscible phases, thereby enhancing reaction rates and selectivity. In particular, PTC enables efficient migration of organosulfur substrates from the hydrocarbon matrix into an aqueous phase where they are oxidized and subsequently extracted. The review first summarizes the deployment of classic PTC systems—quaternary ammonium salts, crown ethers, and related agents—in ODS operations and then delineates the underlying phase-transfer mechanisms, encompassing reaction-controlled, thermally triggered, photo-responsive, and pH-sensitive cycles. Attention is next directed to a new generation of catalysts, including quaternary-ammonium polyoxometalates, imidazolium-substituted polyoxometalates, and ionic-liquid-based hybrids. Their tailored architectures, catalytic performance, and mechanistic attributes are analyzed comprehensively. By incorporating multifunctional supports or rational structural modifications, these systems deliver superior desulfurization efficiency, product selectivity, and recyclability. Despite such progress, commercial deployment is hindered by the following outstanding issues: long-term catalyst durability, continuous-flow reactor design, and full life-cycle cost optimization. Future research should, therefore, focus on elucidating structure–performance relationships, translating batch protocols into robust continuous processes, and performing rigorous environmental and techno-economic assessments to accelerate the industrial adoption of PTC-enabled desulfurization. Full article

In wet flue gas desulfurization and denitrification processes, nitrite accumulation inhibits denitrification efficiency and induces secondary pollution due to its acidic disproportionation. This study developed a Mn-modified ZSM-5 zeolite catalyst, achieving efficient resource conversion of nitrite in nitrogen-containing wastewater through an O₃ + Mn/ZSM-5 catalytic system. Mn/ZSM-5 catalysts with varying SiO₂/Al₂O₃ ratios (prepared by wet impregnation) were characterized by BET, XRD, and XPS. Experimental results demonstrated that Mn/ZSM-5 (SiO₂/Al₂O₃ = 400) exhibited a larger specific surface area, enhanced adsorption capacity, abundant surface Mn³⁺/Mn⁴⁺ species, hydroxyl oxygen species, and chemisorbed oxygen, leading to superior oxidation capability and catalytic activity. Under the optimized conditions of reaction temperature = 40 °C, initial pH = 4, Mn/ZSM-5 dosage = 1 g/L, and O₃ concentration = 100 ppm, the $\mathrm{N}{\mathrm{O}}_2^{-}$ oxidation efficiency reached 94.33%. Repeated tests confirmed that the Mn/ZSM-5 catalyst exhibited excellent stability and wide operational adaptability. The synergistic effect between Mn species and the zeolite support significantly improved ozone utilization efficiency. The O₃ + Mn/ZSM-5 system required less ozone while maintaining high oxidation efficiency, demonstrating better cost-effectiveness. Mechanism studies revealed that the conversion pathway of $\mathrm{N}{\mathrm{O}}_2^{-}$ followed a dual-path catalytic mechanism combining direct ozonation and free radical chain reactions. Practical spray tests confirmed that coupling the Mn/ZSM-5 system with ozone oxidation flue gas denitrification achieved over 95% removal of liquid-phase $\mathrm{N}{\mathrm{O}}_2^{-}$ byproducts without compromising the synergistic removal efficiency of NO_x/SO₂. This study provided an efficient catalytic solution for industrial wastewater treatment and the resource utilization of flue gas denitrification byproducts. Full article

To address the challenge of ultra-deep desulfurization in fuels, a series of heteropolyacid-based poly(ionic liquid) catalysts (C4-PIL@PW, C8-PIL@PW, and C16-PIL@PW) were synthesized via radical polymerization and anion exchange methods. The prepared catalysts were characterized via FT-IR, XRD pattern, and Raman spectroscopy. Optimal reaction parameters (e.g., temperature, catalyst dosage, and O/S molar ratio) were systematically investigated, as well as the catalytic mechanism. The typical sample C8-PIL@PW exhibited exceptional oxidative desulfurization (ODS) performance, achieving a sulfur removal of 99.2% for dibenzothiophene (DBT) without any organic solvent as extractant. Remarkably, the sulfur removal could still retain 89% after recycling five times without regeneration. This study provides a sustainable and high-efficiency catalyst for ODS, offering insights into fuel purification strategies. Full article

Nanopowders of hydroxyapatite (HA) and Fe-substituted hydroxyapatite (HAFe) were synthesized by wet precipitation on either MCM-41 (a synthetic, mesoporous aluminosilicate material) or an aluminum-containing MCM-41 (AlMCM) support. According to X-ray diffraction data, all of the synthesized materials are composite powders consisting of amorphous silicate and an HA phase with low crystallinity. The presence of aluminum and iron in the structure of the powders resulted in further amorphization. The obtained samples showed high specific surface areas (SSAs), ranging from 162.3 to 186.6 m²/g for MCM-41-HA and from 112.6 to 127.2 m²/g for AlMCM-HA. The hysteresis loops were found to be of type H3, indicating the formation of slit-like pores in the intercrystalline space, as confirmed by transmission electron microscopy, which revealed the presence of lamellar and flake-like particles. Catalytic activity tests showed that the conversion of dibenzothiophene depended on the iron concentration in the material and the acidity of the support. To further improve the catalytic activity of the materials, they were impregnated with molybdenum compounds. Active molybdenum peroxo complexes formed under these conditions enabled 100% conversion of dibenzothiophene. To our knowledge, this is the first study on the influence of MCM-41-HA- or AlMCM-HA-based materials on dibenzothiophene conversion via oxidative desulfurization using hydrogen peroxide as an oxidant. Full article

In this study, catalytically active coatings on titanium were synthesized by plasma electrolytic oxidation (PEO) in aqueous electrolytes based on sodium tungstate with the addition of sodium phosphate or sodium borate and chelate complexes of iron, cobalt or nickel. Taking into account the EDX, XPS and XRD data, the oxide–phosphate coatings (PWFe, PWCo, PWNi) contained crystalline titanium oxide and amorphous tungstates and/or phosphates of iron triad metals. Amorphization was facilitated by high phosphorus concentrations (up to 6 at.%). Replacing phosphate with borate in the electrolyte with Ni(II)-EDTA complexes led to the crystallization of WO₃ and NiWO₄ in the PEO coatings (BWNi). All formed PEO coatings were active in reactions of the oxidative desulfurization (ODS) of thiophene and dibenzothiophene and oxidative denitrogenation (ODN) of pyridine, as well as in the simultaneous removal of S- and N-containing substrates from their mixture. The stability of samples with MWO₄ increased in the following series: PWNi < PWCo < PW < PWFe < BWNi. Replacing phosphate with borate in the electrolyte resulted in the preparation of catalysts with enhanced stability and activity. In contrast to PWM catalysts, the BWNi catalyst had selectivity toward the oxidation of pyridine in its mixture with thiophene. Full article

NbVO_x mixed oxides were synthesized, characterized, and evaluated as catalysts for the extractive catalytic oxidative desulfurization (ECODS) of dibenzothiophene (DBT) using acetonitrile as a solvent. The mixed oxides were prepared using two different vanadium precursors: ammonium metavanadate and vanadium(IV)-oxy acetylacetonate. These precursors influenced the acidic/basic properties and the concentration of oxygen vacancies in the resulting catalysts. The texture and surface properties of the synthesized materials were analyzed using nitrogen adsorption/desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–visible spectroscopy (UV-vis). Their catalytic activity was evaluated through the dehydration and dehydrogenation of 2-propanol and the ECODS of DBT. The mixed oxides synthesized with an excess of ammonium metavanadate (Nb:V = 1:2) demonstrated superior catalytic activity in removing DBT from the oil phase, achieving approximately 90% removal within 90 min at 60 °C. This enhanced activity is attributed to its higher acidity, greater concentration of oxygen vacancies, and the presence of vanadium peroxo ligands on its surface. Full article

The environmental and health impacts of sulfur compounds in fuel oil have prompted considerable research interest in oxidative desulfurization (ODS) technology. Tetrahedrally coordinated titanium has been demonstrated to exhibit excellent activity in the context of oxidative desulfurization processes. However, further improving the catalytic property of the tetrahedrally coordinated titanium remains a challenging endeavor. In the context of ODS processes conducted at near room temperatures, the improvement of conversion remains a subject of considerable challenge. In this study, hierarchically porous titanosilicate hollow spheres were synthesized by using TS-1 zeolite precursors as Ti and Si sources to obtain the catalyst with only tetrahedrally coordinated titanium. The synthesized materials were characterized through transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet–visible diffuse reflectance spectroscopy (UV-Vis), and nitrogen adsorption analysis. These techniques confirmed the formation of hollow spherical hierarchically porous structures with Ti species uniformly incorporated in tetrahedral coordination and the presence of five-member rings of TS-1 zeolite. As a result, the hierarchically porous titanosilicate hollow spheres demonstrated excellent catalytic performance in ODS, achieving complete dibenzothiophene (DBT) removal within 15 min and a high turnover frequency (TOF) of up to 123 h⁻¹ at 30 °C. Full article

The oxidative desulfurization (ODS) of heavy fuel oil (HFO) offers a promising solution for desulfurizing marine fuels under mild conditions, in line with current environmental regulations. While most studies focus on model or light fuels, explaining deactivation through leaching or sulfone adsorption, the deactivation mechanisms of catalysts in HFO remain poorly understood. In this work, Mo-based catalysts supported on alumina were extensively characterized before and after catalytic reactions, and regeneration through air calcination was considered. Techniques such as XRD, Raman spectroscopy, XRF, and TGA, alongside catalytic testing with H₂O₂ as an oxidant, revealed that Mo surface speciation significantly impacted both activity and deactivation. Contrary to well-dispersed polymolybdates, crystalline MoO₃ induced low activity and hindered regeneration. No leaching of the active phase was demonstrated during the reaction. Sulfone adsorption had minimal impact on deactivation, while non-sulphur compounds appeared to be the key contributors. Regeneration outcomes were found to be molybdenum content-dependent: 10Mo/Al recovered its activity, while 20Mo/Al formed inactive phases, like Al₂(MoO₄)₃. Using an organic oxidant (tBHP) during ODS influenced the regeneration, as it prevented Al₂(MoO₄)₃ formation and redispersed crystalline MoO₃, enhancing performance. These findings advance understanding of catalyst deactivation and suggest strategies to extend catalyst life in the ODS of HFO. Full article

In this work, a novel heterogeneous catalyst consisting of peroxophosphotungstate, microporous MOF-808, and mesoporous SBA-15 was synthesized, characterized, and used to remove sulfides from model fuel. The prepared material, PW₄@MOF-808@SBA-15, exhibits excellent catalytic activity with a desulfurization efficiency of 99.8% in 60 min for multicomponent simulated fuel, and the desulfurization rate can reach more than 90% after ten consecutive cycles. The excellent catalytic activity and reusability are attributed to the hierarchically porous hybrid material MOF-808@SBA-15, which can effectively encapsulate PW₄ and provide a site for the oxidation of sulfides. Full article

Novel and highly stable nitronyl nitroxide radical (NIT) derivatives were synthesized and coated on the surface of multi-walled carbon nanotubes (MWCNTs) to improve their desulfurization performance. They were characterized by FTIR, UV-vis, SEM, XRD, Raman spectroscopy and ESR. Thiophene in fuel was desulfurized by molecular O₂, and the oxidation activity of these compounds was evaluated. At a normal temperature and pressure, the degradation rates of thiophene by four compounds in 4 h can reach 92.66%, 96.38%, 93.25% and 89.49%, respectively. The MWCNTs/NIT-F have a high special activity for the degradation of thiophene, and their desulfurization activity can be recycled for five times without a significant reduction. The mechanistic studies of MWCNTs/NIT composites show that the ammonium oxide ion is the key active intermediate in catalytic oxidative desulfurization, which provides a new choice for fuel oxidative desulfurization. The results show that NIT significantly improves the photocatalytic performance of MWCNTs. Full article

In recent years, TiO₂-based catalysts have received extensive attention from researchers for their excellent oxidative desulfurization (ODS) performances. In this paper, a series of mesoporous TiO₂/SiO₂ catalysts with different TiO₂ loadings are prepared, using an incipient wetness impregnation method with agricultural waste rice husk as both the silicon source and mesoporous template and tetrabutyl titanate as the titanium source. The effect of different TiO₂ loadings on the ODS performance of the samples is investigated, and the appropriate TiO₂ loading is 2.5%. Compared with pure TiO₂, the 2.5%TiO₂/SiO₂ sample exhibits high catalytic activity for oxidative desulfurization. This is, on the one hand, due to the high specific surface area and mesopore volume of the 2.5%TiO₂/SiO₂ sample. On the other hand, it is due to the uniform dispersion of TiO₂ grains with an average diameter of 6.1 nm on the surface of the mesoporous SiO₂ carrier, which greatly increases the active sites of the 2.5%TiO₂/SiO₂ sample, thus improving the catalytic activity of the sample. The recycling performances of the 2.5%TiO₂/SiO₂ sample are further investigated. The results show that, after fifteen cycles, the 2.5%TiO₂/SiO₂ sample still maintains high conversions of dibenzothiophene (99.8%) and 4,6-dimethyldibenzothiophene (99.7%) without deactivation. In addition, the 2.5%TiO₂/SiO₂ sample treated with TBHP aqueous solution is characterized by the technique of UV-Vis, and the Ti-peroxo (Ti-OO^tBu) species, the active intermediate for the ODS of bulky organic sulfides, is successfully captured. Finally, a possible reaction mechanism for the ODS process over the 2.5%TiO₂/SiO₂ sample is proposed. Full article

One of the current challenges is the reduction of sulfur emitted into the atmosphere, usually in the form of sulfur oxides generated by fossil fuel combustion. To achieve this goal, the sulfur content should be reduced in fuel. In this context, vanadium-containing materials based on SBA-15 mesoporous silica supports and two different sources of vanadium were prepared, characterized, and applied as catalysts for oxidative desulfurization (CODS) and extractive oxidative desulfurization processes (ECODSs). The novelty of this work was the comparative study of vanadium-containing materials in two desulfurization systems. The properties of the catalysts, the concentration and state of vanadium species, and their role in the catalytic process were examined by low-temperature nitrogen physisorption, XRD, UV-Vis, XPS, and chemisorption of pyridine combined with FTIR spectroscopy. The catalytic performance of the material prepared using ammonium metavanadate was superior to that of the catalyst obtained using vanadium(IV) oxide sulfate, which was explained by a higher concentration of vanadium species on the surface of the support and their lower oxidation state in the former. Both types of catalysts showed high activity and stability in the ECODS process. Full article

With increasingly stringent emission limits on sulfur and sulfur-containing substances, the reduction and removal of sulfur compounds from fuels has become an urgent task. Emissions of sulfur-containing compounds pose a significant threat to the environment and human health. Ionic liquids (ILs) have attracted much attention in recent years as green solvents and functional materials, and their unique properties make them useful alternatives to conventional desulfurization organic solvents. This paper reviews the advantages and disadvantages of traditional desulfurization technologies such as hydrodesulfurization, oxidative desulfurization, biological desulfurization, adsorptive desulfurization, extractive desulfurization, etc. It focuses on the synthesis of ionic liquids and their applications in oxidative desulfurization, extractive desulfurization, extractive oxidative desulfurization, and catalytic oxidative desulfurization, and it analyzes the problems of ionic liquids that need to be solved urgently in desulfurization, looking forward to the development of sulfuric compounds as a kind of new and emerging green solvent in the field of desulfurization. Full article

Titanium silicon molecular zeolite (TS-1) plays an important role in catalytic reactions due to its unique nanostructure. The straight channel on TS-1 was parallel to the orientation of the short b-axis and directly exposed to the aperture of the 10-member ring with a diameter of 0.54 nm × 0.56 nm. This structure could effectively reduce the diffuse restriction of bulk organic compounds during the oxidative desulfurization process. As a kind of cationic polymer electrolyte, polydimethyldiallyl ammonium chloride (PDDA) contains continuous [C₈H₁₆N⁺Cl⁻] chain segments, in which the Cl⁻ could function as an effective structure-directing agent in the synthesis of nanomaterials. The chain of PDDA could adequately interact with the [0 1 0] plane in the preparation process of zeolite, and then the TS-1 nanosheet with short b-axis thickness (6 nm) could be obtained. The pore structure of the TS-1 nanosheet is controlled by regulating the content of PDDA. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N₂ physical adsorption analysis, infrared absorption spectrum and ultraviolet–visible spectrum were used to determine the TS-1. The thinner nanosheets exhibit excellent catalytic performance in oxidative desulfurization of dibenzothiophene (DBT), in which the removal rate could remain at 100% after three recycles. Here, the TS-1 nanosheet with short b-axis thickness has a promising future in catalytic reactions. Full article

The sulfur in petroleum coke is harmful to carbon products, underscoring the importance of desulfurization for high-sulfur petroleum coke. This paper proposes a method combining alkaline catalytic roasting with ultrasonic oxidation for the deep desulfurization of high-sulfur petroleum coke. The results show that the desulfurization rate reaches 88.99% and the sulfur content is reduced to 0.83 wt.% under a coke particle size of 96–75 μm, sodium-hydroxide-to-petroleum-coke ratio of 50%, roasting temperature of 700 °C, and holding time of 2 h. The alkali-calcined petroleum coke is ultrasonically oxidized and desulfurized in peracetic acid. The results show that, under a hydrogen peroxide content of 10%, hydrogen-peroxide-(liquid)-to-petroleum-coke (solid) ratio of 20 mL/g, acetic acid content of 5 mL, ultrasonic power of 300 W, reaction temperature of 60 °C, and reaction duration of 4 h, the sulfur content is reduced to 0.15 wt.% and the total desulfurization reaches 98.01%. Through a series of characterizations, the proposed desulfurization mechanism is verified. Alkali roasting effectively removes a significant portion of sulfur in petroleum coke. However, the elimination of certain sulfur compounds, such as the more complex thiophene, presents challenges. The thiophene content is subsequently removed via ultrasonic oxidation. Full article