Oxidative Desulfurization Using Polyoxometalates

Facile Construction of Magnetic Ionic Liquid Supported Silica for Aerobic Oxidative Desulfurization in Fuel

With the rapid growth in fuel demand, deep desulfurization of fuel oil is vitally necessary for the sake of health and environmental protection. In this work, a kind of magnetic ionic liquid supported silica is prepared by a facile ball milling method, and applied in the aerobic oxidative desulfurization of organosulfurs in fuel. The experimental results indicated that ball milling procedure can increase the specific surface area of samples, which is beneficial to oxidative desulfurization process. Under the optimal reaction conditions, the prepared materials can have an entire removal of aromatic sulfur compounds as well as a good recycling ability. Moreover, the introduction of Fe3O4 did not decline the desulfurization performance, but help the catalyst to be easily separated after reaction.

Nanocatalysts for Oxidative Desulfurization of Liquid Fuel: Modern Solutions and the Perspectives of Application in Hybrid Chemical-Biocatalytic Processes

In this paper, the current advantages and disadvantages of using metal-containing nanocatalysts (NCs) for deep chemical oxidative desulfurization (ODS) of liquid fuels are reviewed. A similar analysis is performed for the oxidative biodesulfurization of oil along the 4S-pathway, catalyzed by various aerobic bacterial cells of microorganisms. The preferences of using NCs for the oxidation of organic sulfur-containing compounds in various oil fractions seem obvious. The text discusses the development of new chemical and biocatalytic approaches to ODS, including the use of both heterogeneous NCs and anaerobic microbial biocatalysts that catalyze the reduction of chemically oxidized sulfur-containing compounds in the framework of methanogenesis. The addition of anaerobic biocatalytic stages to the ODS of liquid fuel based on NCs leads to the emergence of hybrid technologies that improve both the environmental characteristics and the economic efficiency of the overall process. The bioconversion of sulfur-containing extracts from fuels with accompanying hydrocarbon residues into biogas containing valuable components for the implementation of C-1 green chemistry processes, such as CH4, CO2, or H2, looks attractive for the implementation of such a hybrid process.

Aerobic Oxidative Desulfurization of Liquid Fuel Catalyzed by P–Mo–V Heteropoly Acids in the Presence of Aldehyde

Aerobic oxidative desulfurization (ODS) of model liquid fuel (dodecane spiked with dibenzothiophene (DBT)) was carried out in the presence of bulk and supported Keggin-type heteropoly acids H3+nPMo12-nVnO40 (HPA-n, n = 0–3) as heterogeneous catalysts and benzaldehyde as a sacrificial reductant. In the presence of bulk H4PMo11VO40 (HPA-1), 100% of DBT was removed from fuel (converted to DBT sulfone) at 60 °C and ambient air pressure. Multiple catalyst reuse without loss of activity was demonstrated. The ODS reaction was strongly inhibited by radical scavengers. An unbranched radical chain mechanism was proposed.

A current overview of the oxidative desulfurization of fuels utilizing heat and solar light: from materials design to catalysis for clean energy

The ceaseless increase of pollution cases due to the tremendous consumption of fossil fuels has steered the world towards an environmental crisis and necessitated urgency to curtail noxious sulfur oxide emissions. Since the world is moving toward green chemistry, a fuel desulfurization process driven by clean technology is of paramount significance in the field of environmental remediation. Among the novel desulfurization techniques, the oxidative desulfurization (ODS) process has been intensively studied and is highlighted as the rising star to effectuate sulfur-free fuels due to its mild reaction conditions and remarkable desulfurization performances in the past decade. This critical review emphasizes the latest advances in thermal catalytic ODS and photocatalytic ODS related to the design and synthesis routes of myriad materials. This encompasses the engineering of metal oxides, ionic liquids, deep eutectic solvents, polyoxometalates, metal-organic frameworks, metal-free materials and their hybrids in the customization of advantageous properties in terms of morphology, topography, composition and electronic states. The essential connection between catalyst characteristics and performances in ODS will be critically discussed along with corresponding reaction mechanisms to provide thorough insight for shaping future research directions. The impacts of oxidant type, solvent type, temperature and other pivotal factors on the effectiveness of ODS are outlined. Finally, a summary of confronted challenges and future outlooks in the journey to ODS application is presented.

Highly efficient Co(II) porphyrin catalysts for the extractive oxidative desulfurization of dibenzothiophene in fuel oils under mild conditions

Co(II) porphyrins have been utilized as efficient and selective catalysts for the extractive oxidative desulfurization reaction on the refractory dibenzothiophene (DBT) in [Formula: see text]-dodecane (model middle distillate fuel oil). The acetonitrile was taken as extracting polar solvent and H2O2 was used as oxidant. The reaction optimization was done with respect to DBT:catalyst molar ratio; DBT:H2O2 molar ratio; extracting solvent: CH3CN/[Formula: see text]-dodecane volume ratio; reaction temperature and time. Under the optimized conditions, a maximum of [Formula: see text]98% DBT removal was achieved by using the meso-tetrakis(4[Formula: see text] methoxyphenyl)porphyrinatocobalt(II) as catalyst under mild conditions at 50[Formula: see text]C.

Confining Polyoxometalate Clusters into Porous Aromatic Framework Materials for Catalytic Desulfurization of Dibenzothiophene

Removal of notorious sulfur compounds to produce low-sulfur-content (≤10 ppm) diesel is necessary and vital for modern industry and environmental protection. A new type of inorganic-organic hybrid material has been designed and synthesized via confining molybdenum-containing polyoxometalate (POM) clusters within porous aromatic framework-1 (PAF-1) cavities named POM-PAF-1. Deep oxidative desulfurization experiments reveal that POM-PAF-1 possesses excellent reactivity under mild conditions, exemplified by a sulfur removal degree of 98.5% dibenzothiophene within 30 min at 30 °C. The improvement in oxidative desulfurization reactivity from traditional porous POM-based catalysts is owing to uniform POMs and lipophilic and porous PAF-1. The high performance of POM-PAF-1 in terms of excellent reactivity and good stability means it has potential in new heterogeneous catalysis.

Ultrasound assisted oxidative deep-desulfurization of dimethyl disulphide from turpentine

A promising approach of ultrasound assisted oxidative desulfurization (UAOD) was studied for deep desulfurization of simulated sulphated turpentine containing dimethyl disulphide (DMDS) as model pollutant. The effect of ultrasound parameters such as power (80-120 W) and duty cycle (50-80%) as well as operating conditions as initial concentration (50-100 ppm), volume (100-300 ml) and temperature (28 °C as ambient condition, 50-70 °C) on the extent of desulfurization have been studied. The effect of addition of various oxidizing agents such as hydrogen peroxide over the range of 3-18 g/L, Fenton reagent by varying FeSO₄ loading from 0.75 g/L to 1.75 g/L at constant H₂O₂ loading and titanium dioxide (loading over the range 1-4 g/L) in the presence of ultrasonic horn have also been investigated at laboratory scale. The addition of oxidizing agents in presence of ultrasound enhanced the extent of DMDS removal. The extent of desulfurization was found to be remarkably low for individual approaches as compared to combination approaches of US/oxidizing agents. The kinetic analysis revealed that oxidation follows first order kinetics. A significant increase in cavitational yield was observed for combination approach of US/H₂O₂/TiO₂ (5.78 × 10^-9 g/L) compared to individual ultrasound approach (2.04 × 10^-9 g/L). Under best conditions of 120 W power, 70% duty cycle, 50 ppm initial concentration, 15 g/L H₂O₂ loading and 4 g/L TiO₂ loading, 100% desulfurization was obtained at 23.19 Rs/L as the treatment cost. Based on the obtained results it can be concluded that US/H₂O₂/TiO₂ approach is highly efficient desulfurization technique for deep desulfurization of simulated sulphated turpentine.

Catalytic oxidative desulphurization of gasoline using amphiphilic polyoxometalate@polymer nanocomposite as an efficient, reusable, and green organic-inorganic hybrid catalyst

To preparation of ultra-clean gasoline fuel, a new amphiphilic nanocomposite (TBA-SiWMn@PVA) has been successfully synthesized by supporting sandwich-type silicotungstate polyoxometalate ((n-C₄H₉)₄N)₇H₅Si₂W₁₈Mn₄O₆₈ (TBA-SiWMn) on polyvinylalcohol (PVA) as an efficient catalyst for catalytic oxidative desulphurization (CODS) of gasoline. The synthesized materials were characterized by means of elemental analysis, ¹¹³Mn NMR, ²⁹Si NMR, XRD, SEM, FT-IR and UV-vis techniques. The catalytic activity of TBA-SiWMn@PVA nanocomposite was tested on real gasoline in the presence of CH₃COOH/H₂O₂ as an oxidant and the results were compared with model sulphur compounds at the same conditions. The TBA-SiWMn@PVA nanocomposite was shown excellent catalytic performance and recoverability for ODS of gasoline with high yield. The effects of the reaction time, reaction temperature, dosage and nature of catalyst were investigated. The reaction mechanism and the kinetic parameters of sulphur compounds oxidation were also discussed. The probable mechanism was proposed via the electrophilic mechanism through the formation of a peroxometalate intermediate complex with phase transfer properties. Results were indicated that the kinetics of sulphur oxidation fitted the pseudo-first-order kinetic model. After 5 oxidation runs, the heterogeneous nanocatalyst was separated and recovered easily.

Deep Oxidative Desulfurization of Fuels in the Presence of Brönsted Acidic Polyoxometalate-Based Ionic Liquids

Polyoxometalate-based ionic liquid hybrid materials with a pyridinium cation, containing Brönsted acid sites, were synthesized and used as catalysts for the oxidation of model and real diesel fuels. Keggin-type polyoxometalates with the formulae [PMo12O40]3-, [PVMo11O40]4-, [PV2Mo10O40]4-, [PW12O40]3- were used as anions. It was shown that increasing the acid site strength leads to an increase of dibenzothiophene conversion to the corresponding sulfone. The best results were obtained in the presence of a catalyst, containing a nicotinic acid derivative as cation and phosphomolybdate as anion. The main factors affecting the process consisting of catalyst dosage, temperature, reaction time, oxidant dosage were investigated in detail. Under optimal conditions full oxidation of dibenzothiophene and more than a 90% desulfurization degree of real diesel fuel (initial sulfur content of 2050 ppm) were obtained (the oxidation conditions: NK-1 catalyst, molar ratio H2O2:S 10:1, molar ratio S:Mo 8:1, 1 mL MeCN, 70 °C, 1 h). The synthesized catalysts could be used five times with a slight decrease in activity.

Oxidative desulfurization of dibenzothiophene catalyzed by molybdenum dioxide immobilized on zirconia-modified silica

MoO₂/ZrO₂–SiO₂ catalysts show high activity in the oxidative desulfurization reaction, and the desulfurization rate can reach 99.96%.

Deep oxidative desulfurization of model fuels catalyzed by polyoxometalates anchored on amine-functionalized ceria doped MCM-41 with molecular oxygen

The synergistic effect between the vanadium-substituted POM and ceria doped MCM-41 results in extraordinary catalytic activity for oxidative desulfurization.

[HDMF]Cl-based DES as highly efficient extractants and catalysts for oxidative desulfurization of model oil

N,N-Dimethylformamide hydrochloric acid/XMCl_n ([HDMF]Cl/XMCl_n, M = Zn or Fe, n = 2 or 3) was synthesized by stirring the mixture of [HDMF]Cl and metal chloride. [HDMF]Cl-based DES was characterized by FT-IR spectroscopy, ESI-MS and ¹H-NMR spectroscopy. The oxidative desulfurization activity was investigated using [HDMF]Cl/0.2FeCl₃ and [HDMF]Cl/ZnCl₂ as the extractant and catalyst, and hydrogen peroxide (H₂O₂) as the oxidant. The desulfurization rate can reach up to 98.08% and 99.2% for DBT using [HDMF]Cl/0.2FeCl₃ and [HDMF]Cl/ZnCl₂, respectively. After recycling for 7 times, the removal rate of DBT still can reach more than 97%.

[HDMF]Cl/XMCl_n exhibits high desulfurization activity. Meanwhile, the DES saving a lot of N,N-dimethylformamide protects environment.

A new phosphotungstate-supported rhenium carbonyl derivative: synthesis, characterization and catalytic selective oxidation of thiophenes

We synthesized a new phosphotungstate-supported rhenium carbonyl derivative, [N(CH₃)₄]₆H₄[P₂W₁₇O₆₂{Re(CO)₃}₂]·25H₂O, existing the first {Re₂} fragment. Moreover, it also exhibits high efficiency for the selective oxidation of thiophenes.

Effect of Preparation Method on Ag Modified Ti-HMS Catalyst Structure and Catalytic Oxidative Desulfurization Performance

Ag modified mesoporous molecular sieves Ti-HMS were prepared by in-situ synthesis (Ag/Ti-HMS-I), deposition-precipitation method (Ag/Ti-HMS-D) and ultrasound-assisted impregnation methods (Ag/Ti-HMS-U), respectively. The catalytic performance of catalysts in the oxidative desulfurization(ODS) of benzothiophene with hydrogen peroxide (H2O2) has been investigated. The physicochemical properties of the catalysts were characterized by XRD, SEM, BET and FT-IR techniques. Experimental results showed that the catalyst Ag/Ti-HMS-U exhibited the best catalytic activity, and this maybe because the catalyst possessed relatively good mesoporous structure and high Ag dispersion. Under the best operating condition for the catalytic oxidative desulfurization: temperature 60 °C, atmospheric pressure, 0.1 g catalysts, 8 molar ratio of hydrogen peroxide to sulfur, using acetonitrile as extraction solvent for double extraction, the sulfur content in model diesel fuel (MDF) was reduced from 800 ppm to 17 ppm with 97.8% of total sulfur after 1 h.

Probing the Catalytic Activity of Sulfate-Derived Pristine and Post-Treated Porous TiO2(101) Anatase Mesocrystals by the Oxidative Desulfurization of Dibenzothiophenes

Mesocrystals (basically nanostructures showing alignment of nanocrystals well beyond crystal size) are attracting considerable attention for modeling and optimization of functionalities. However, for surface-driven applications (heterogeneous catalysis), only those mesocrystals with excellent textural properties are expected to fulfill their potential. This is especially true for oxidative desulfuration of dibenzothiophenes (hard to desulfurize organosulfur compounds found in fossil fuels). Here, we probe the catalytic activity of anatases for the oxidative desulfuration of dibenzothiophenes under atmospheric pressure and mild temperatures. Specifically, for this study, we have taken advantage of the high stability of the (101) anatase surface to obtain a variety of uniform colloidal mesocrystals (approximately 50 nm) with adequate orientational order and good textural properties (pores around 3-4 nm and surface areas around 200 m²/g). Ultimately, this stability has allowed us to compare the catalytic activity of anatases that expose a high number of aligned single crystal-like surfaces while differing in controllable surface characteristics. Thus, we have established that the type of tetrahedral coordination observed in these anatase mesocrystals is not essential for oxidative desulfuration and that both elimination of sulfates and good textural properties significantly improve the catalytic activity. Furthermore, the most active mesocrystals have been used to model the catalytic reaction in three-(oil-solvent-catalyst) and two-phase (solvent-catalyst) systems. Thus, we have been able to observe that the transfer of DBT from the oil to the solvent phase partially limits the oxidative process and to estimate an apparent activation energy for the oxidative desulfuration reaction of approximately 40 kJ/mol in the two-phase system to avoid mass transfer limitations. Our results clearly establish that (101) anatase mesocrystals with excellent textural properties show adequate stability to withstand several post-treatments without losing their initial mesocrystalline character and therefore could serve as models for catalytic processes different from the one studied here.

Propionic acid-based deep eutectic solvents: synthesis and ultra-deep oxidative desulfurization activity

Propionic acid-based deep eutectic solvents (C₃H₆O₂/X ZnCl₂, X from 0.1 to 0.6) were synthesized by stirring a mixture of propionic acid and zinc chloride at 100 °C.

Ultrasound-assisted oxidative desulfurization process of liquid fuel by phosphotungstic acid encapsulated in a interpenetrating amine-functionalized Zn(II)-based MOF as catalyst

In this work, ultrasound-assisted oxidative desulfurization (UAOD) of liquid fuels performed with a novel heterogeneous highly dispersed Keggin-type phosphotungstic acid (H₃PW₁₂O₄₀, PTA) catalyst that encapsulated into an amino-functionalized MOF (TMU-17-NH₂). The prepared composite exhibits high catalytic activity and reusability in oxidative desulfurization of model fuel. Ultrasound-assisted oxidative desulfurization (UAOD) is a new way to performed oxidation reaction of sulfur-contain compounds rapidly, economically, environment-friendly and safely, under mild conditions. Ultrasound waves can be apply as an efficient tool to decrease the reaction time and improves oxidative desulfurization system performance. PTA@TMU-17-NH₂ could be completely performed desulfurization of the model oil by 20mg of catalyst, O/S molar ratio of 1:1 in presence of MeCN as extraction solvent. The obtained results indicated that the conversions of DBT to DBTO₂ achieve 98% after 15min in ambient temperature. In this work, we prepared TMU-17-NH₂ and PTA/TMU-17-NH₂ composite by ultrasound irradiation for first time and employed in UAOD process. Prepared catalyst exhibit an excellent reusability without PTA leaching and loss of activity.

Efficient concurrent removal of sulfur and nitrogen contents from complex oil mixtures by using polyoxometalate-based composite materials

Efficient and simultaneous deep desulfurization and denitrogenation of complex oil systems under mild conditions is reported using a heterogeneous Tris-LDH-LaW₁₀ catalyst.

Influence of a porous MOF support on the catalytic performance of Eu-polyoxometalate based materials: desulfurization of a model diesel

An aluminum 2-aminoterephthalate based metal–organic framework material was used to prepare highly efficient heterogeneous catalysts in desulfurization processes.

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

Supported ionic liquid catalyst [Bmim]FeCl₄/Am TiO₂ was synthesized and showed excellent desulfurization efficiency and reuseable performance in the ECODS system.

Catalytic system for pyridine oxidation to N-oxides under mild conditions based on polyoxomolybdate

A reusable and effective catalytic system has been developed for oxidation of pyridines catalyzed by Keplerate polyoxomolybdate ({Mo₁₃₂}) at room temperature. Pyridine compounds could be oxidized in high yields under mild conditions.

Magnetic amphiphilic nanocomposites based on silica–carbon for sulphur contaminant oxidation

Magnetic amphiphilic nanocomposites based on silica–carbon promote the desulfurization of diesel fuel and their activity is enhanced by Mo nuclei supported on the surface.

Light irradiation induced aerobic oxidative deep-desulfurization of fuel in ionic liquid

One-pot extraction combined with metal-free photochemical aerobic oxidative deep desulfurization of fuels in ionic liquid was successfully achieved.

Ultra-deep desulfurization via reactive adsorption on peroxophosphomolybdate/agarose hybrids

A catalyst system composed of peroxophosphomolybdates as catalytic center and agarose as matrix material had been designed. The [C16H33N(CH3)3]3[PO4{MoO(O2)2}4]/agarose (C16PMo(O2)2/agarose) hybrid was found to be active for oxidation desulfurization (ODS) of dibenzothiophene (DBT) or real fuel into corresponding sulfone by H2O2 as an oxidant, while the sulfur content could be reduced to 5ppm. The higher activity comes from its components including [PO4{MoO(O2)2}4] catalytic sites, the hydrophobic quaternary ammonium cation affinity to low polarity substrates, and agarose matrix affinity to H2O2 and sulfone. During the oxidative reaction, the mass transfer resistance between H2O2 and organic sulfurs could be decreased and the reaction rate could increase by the assistance of agarose and hydrophobic tails of [C16H33N(CH3)3]3[PO4{MoO(O2)2}4]. Meanwhile, the oxidative products could be adsorbed by agarose matrix to give clean fuel avoiding the post-treatment. In addition, the hybrid was easily regenerated to be reused.