Oxidation Of DBT Research Articles

Facile fabrication of confined spaces with molybdenum atoms for fast oxidative desulfurization of fuel oil

Molybdenum-based heterogeneous catalysts are promising for oxidative desulfurization (ODS) of fuel oil. However, the catalytic activity is linked with the dispersibility of Mo atoms on appropriate carriers. Here, Mo-based mesoporous silica was constructed by using confined spaces of as-synthesized SBA-15 (AS), where Mo atoms are homogeneously dispersed. By utilizing facile solid phase grinding followed by calcination, the Mo precursor was introduced into the confined spaces between template and silica walls to form Mo-O-Si structure during which the template P123 was also released. Characterization results revealed that up to 5 wt% of Mo can be well dispersed while sever aggregation takes place in the catalysts derived from template free SBA-15(CS) at similar loading. Confined spaces and abundant hydroxyl groups played a significant role for Mo dispersion. The catalysts derived from AS showed superior ODS activity to their counterparts derived from CS and converted 100 % of DBT in 25 min at T = 30 °C, O/S = 5 and a catalyst dose of 0.1 g. The kinetic studies revealed that the DBT oxidation follow pseudo-first-order kinetic and the activation energy of DBT calculated via Arrhenius equation is 36.97 kJ/mol and 33.88 kJ/mol over Mo-AS and Mo-CS, respectively. The thermodynamic studies demonstrated that DBT oxidation is endothermic with positive Gibbs free energy, suggesting the non-spontaneity of ODS of DBT over Mo based catalysts. Furthermore, the stability and regeneration capability of Mo-AS made it promising for ODS technology for fuel oil.

Amorphous MoOx loaded on N-doped carbon-modified SiO2 for strongly enhanced oxidative desulfurization activity

Transition-metal oxides (TMOs) are good catalyst candidates for oxidation desulfurization (ODS) reaction, and its excellent dispersion in carriers could exert great influence on its catalytic performance. However, improving its catalytic activity still remains challenging. Herein, the amorphous molybdenum oxide (MoOx) was synthesized as the active sites for ODS reaction. Via a facile adsorption-pyrolysis approach, the amorphous MoOx was dispersedly immobilized onto N-doped carbon layer (NC)-encapsulated SiO2 using zinc pyridine porphyrin (ZnTPyP) and phosphomolybdic acid (PMo12)-modified SiO2 nanocomposites as precursor, obtaining the MoOx@NC@SiO2 catalyst. Owing to the wonderful pre-dispersion of Mo sources on the precursor leaded by the electrostatic interaction and spacial effect, the confinement effect of the derived carbon matrix, and the strong Mo-N bonds, the growth of MoOx crystal could be inhibited in pyrolysis procedure, ensuring the amorphous structure and good dispersion of MoOx species on SiO2. The as-prepared MoOx@NC@SiO2 exhibits excellent oxidation desulfurization (ODS) performances, and could promote the complete oxidation of DBT in model fuel into DBTO2 at the theoretical O/S molar ratio of 2, due to the perfect activation of all oxygen atoms of H2O2 by the amorphous MoOx. In addition, a plausible ODS mechanism over MoOx@NC@SiO2 is depicted to be the •OH radicals. Moreover, MoOx@NC@SiO2 still displays an outstanding reusability over at least 10 cycles owing to the encapsulation of NC layers and the strong Mo-N bonds. Therefore, this work provides a promising catalyst for industrial ODS application, and opens up a new avenue for developing the amorphous TMOs catalysts.

Cobalt-manganese spinel structure catalysts for aerobic oxidative desulfurization

For the first time cobalt-manganese spinel structure catalysts were effectively applied for aerobic oxidation of sulfur-containing compounds. High activity of obtained catalysts is achieved due to the existence of the redox couples Co2+/Co3+ and Mn3+/Mn4+ in the spinel structure. It has been shown that the high mobility of oxygen in the spinel structure contributes to the efficient oxidation of sulfur-containing compounds. The CoMn2O4 and MnCo2O4 spinel-type catalysts were obtained by the hydrothermal method and characterized by a complex of physicochemical methods: XRD, FTIR, nitrogen adsorption–desorption, SEM, TEM, TPR-H2, and XPS. Under optimal conditions (130 °C, ω(cat.) = 0.034 wt%, 2 h), the complete DBT oxidation was achieved in the presence of CoMn2O4. High stability of catalyst over 5 cycles of oxidation was demonstrated. A possible reaction mechanism has been proposed based on EPR data and catalysts characterization results.

Heterogeneous oxidative desulfurization of fuels using amphiphilic mesoporous phosphomolybdate-based poly(ionic liquid) over a wide temperature range

Four new types of amphiphilic polyoxometalate-based poly(ionic liquid) (PDB-PMo, PDO-PMo, PDD-PMo and PDH-PMo) were prepared by ion exchange between poly(ionic liquid) (PIL) and H3PMo12O40 (HPMo), where PIL are copolymerized by hydrophilic 3,3′-methylenebis(1-vinylimidazol) bromine and hydrophobic [3–alkyl–1–vinylimidazolium] bromine (alkyl = C4, PDBBr; alkyl = C8, PDOBr; alkyl = C12, PDDBr and alkyl = C16, PDHBr). Among them, the desulfurization rate of PDD-PMo can reach 100% within a wide temperature range of 0–50 °C, especially at 0 °C, DBT can be completely removed within 100 min. The influences of reaction temperature, molar ratio of H2O2/S, catalyst dosage and different sulfur-containing compounds were investigated. The kinetic study shows that the apparent activation energy of the DBT oxidation reaction is 36.73 ± 1.42 kJ/mol. In addition, EPR analysis and the free radical quenching experiment proved that both active radicals O2•− and HO• played an active role in the oxidative desulfurization (ODS) reaction system and proposed a reasonable reaction mechanism. The introduction of hydrophilic IL monomer is also an efficient strategy to construct amphiphilic polyoxometalate-based poly(ionic liquid), which further implements ultra-deep desulfurization.

LaMnxCo1‐xO3 (x=0, 0.25) Perovskites: Novel Nano Catalysts for Removal of Thiophene compounds in Fuels by Catalytic and Ultrasound‐assisted Oxidative Desulfurization

AbstractLaMnxCo1‐xO3 (x=0, 0.25) perovskites were developed as novel nanocatalysts for the desulfurization of thiophenes compounds by catalytic oxidative desulfurization (CODS) and ultrasound‐assisted oxidative desulfurization (UAOD). The perovskites were synthesized by the sol‐gel auto‐combustion method and characterized by X‐ray diffraction (XRD), temperature programmed reduction (TPR), Scanning electron microscopy (SEM) and BET surface area. The experiments were designed by the Box‐Behnken method of response surface methodology. The catalytic experiments were designed by response surface methodology (RSM). LaMn0.25Co0.75O3 despite having a lower surface area rather than LaCoO3 exhibited superior activity due to easy reducibility and high surface electron density approved by TPR. Pareto analysis indicated that the DBT concentration had the most effect on the CODS process. Ultrasound waves enhanced the activity of the catalysts via the formation of hot spots as an accelerating and de‐agglomerating agent in the UAOD process, leading the LaMn0.25Co0.75O3 to be reusable at least for 5 cycles. A mechanism for DBT oxidation was proposed by the formation of DBT sulfone. Due to steric hindrance and the electron density of the sulfur atoms in thiophene derivatives, the following order resulted in their desulfurization rate: DBT>4‐MDBT>BT. The study indicated that perovskites could be novel and promising nanocatalysts for the desulfurization of fuels.

In situ highly dispersed loading of molybdenum dioxide with oxygen vacancies on N-doped graphene for enhanced oxidative desulfurization of fuel oil

Herein, molybdenum dioxide (MoO2) nanoparticles with a particle size of 1.78 nm was uniformly anchored on nitrogen-doped reduced graphene oxide (NrGO) with strong electron-donating effect by in situ annealing of the precursor composed of polyaniline-modified graphene oxide (PANI/GO) and ammonium molybdate. The as-prepared MoO2/NrGO catalyst at 800 °C showed the excellent oxidative desulfurization (ODS) activity and reusability. In the presence of H2O2, the DBT removal over MoO2/NrGO-800 could reach 99.8 % within 10 min at 60 °C, and it was almost still retained even after 8 cycles. The outstanding ODS performance is importantly ascribed to the following aspects. The electron transfer from electron-rich NrGO to MoO2 could not only weaken Mo-O bonds and improve the small size and dispersion of MoO2, resulting in more oxygen vacancies and exposed active sites, but also reduce the leaching of active sites due to the induced electronstatic interaction. Oxygen vacancies intrinsiclly facilitate the generation of active oxygen intermediates. Radical scavenger experiments and electron paramagnetic resonance (EPR) revealed that during the DBT oxidation over MoO2/NrGO-800, •OH radicals are the major active species, and electron transfer is still an important step.

Crystal Growth Blocking Strategy Enabling Efficient Solvent-Free Synthesis of Hierarchical UiO-66 for Large-Molecule Catalysis

Metal–organic frameworks (MOFs) with rich hierarchical structures have attracted great attention in processes with large molecules, such as catalysis and adsorption. However, efficiently and cost-effectively fabricating hierarchical MOFs with robust stability remains challenging. Herein, we report a crystal growth blocking strategy to prepare hierarchical UiO-66 by a solvent-free method. The addition of FeCl3 to the synthetic system blocks the overgrowth of UiO-66 crystals and limits the particle size to around just 12 nm. After the removal of Fe by ethanol treatment, these small particles loosely aggregate and gain intercrystalline mesopores. The optimal sample Mes-UiO-66 exhibits a well-developed hierarchical structure, the BET surface area reaches 1161.9 m2 g–1, and the mesopore volume attains a state-of-the-art 1.21 cm3 g–1. The superior catalytic performance and the robust stability of Mes-UiO-66 are demonstrated by the oxidation of DBT, in which the DBT conversion surpasses 99% and shows a slight decrease after five cycles. Our finding may provide a novel platform for efficiently fabricating hierarchical MOFs for large-molecule catalysis.

Combined Heterogeneous Catalyst Based on Titanium Oxide for Highly Efficient Oxidative Desulfurization of Model Fuels.

In this work, new heterogeneous Mo-containing catalysts based on sulfonic titanium dioxide were developed for the oxidation of sulfur-containing model feed. The synergistic effect of molybdenum and sulfonic group modifiers allows for enhancing catalytic activity in dibenzothiophene oxidative transformation, and a strong interaction between support and active component for thus obtained catalysts provides increased stability for leaching. For the selected optimal conditions, the Mo/TiO2-SO3H catalyst exhibited 100% DBT conversion for 10 min (1 wt % catalyst, molar ratio of H2O2:DBT, 2:1; 80 °C). Complete oxidation of DBT in the presence of the synthesized catalyst is achieved when using a stoichiometric amount of oxidizing agent, which indicates its high selectivity. The enhanced stability for metal leaching was proved in recycling tests, where the catalyst was operated for seven oxidation cycles without regeneration with retainable activity in DBT-containing model feed oxidation with hydrogen peroxide under mild reaction conditions. In 30 min of the reaction (H2O2:S = 2:1 (mol), 0.5% catalyst, 5 mL of acetonitrile, 80 °C), it was possible to reduce the content of sulfur compounds in the diesel fraction by 88% (from 5600 to 600 ppm).

Facial synthesis of mesoporous {Mo132}/BiOCl for the efficient oxidative desulfurization of fuel

The Keplerate nanoball iso-polyoxomolybdate {Mo132} supported on BiOCl was prepared and assessed as a green, innovative, and low-cost oxidative desulfurization catalyst for dibenzothiophene-containing model oil (DBT). The XRD, FT-IR, Raman, SEM, TEM, BET, and XPS characterize the prepared catalysts. The optimum operating parameters were identified by evaluating factors such as reaction time, catalyst quantity, oxygen to sulfur molar ratio, and temperature. Experiments indicated that the catalyst was greatly efficient in removing DBT, with a sulfur removal rate up to 100 % at optimum conditions (catalyst dosage = 5 g/L, O/S = 10, time = 180 min, and temperature = 40 °C) utilizing hydrogen peroxide (H2O2) as oxidizing agent and acetonitrile as extracting solvent. Furthermore, {Mo132}/BiOCl showed high stability and catalytic activity like that of the fresh one after four cycles. ODS activity of the catalyst was evaluated for various thiophenes (thiophene, BT, 4,6-DMDBT, and DBT) derivative and feed at optimum conditions. The proposed mechanism for catalytic oxidation of DBT in the existence of {Mo132}/BiOCl nanocomposite was studied.

Light-Enhanced Oxidative Adsorption Desulfurization of Diesel Fuel over TiO2–ZrO2 Mixed Oxides

This study explored a new method for the adsorptive desulfurization of liquid hydrocarbon fuels called “light-enhanced oxidative adsorption desulfurization (LEOADS)”, which combines the photo-oxidation of aromatic sulfur compounds with the adsorption of oxidized-sulfur compounds over an adsorbent. The LEOADS of dibenzothiophene in real diesel fuel (DBT/diesel) was conducted in a batch system under UV–vis irradiation at ambient conditions using air as an oxidant. The desulfurization performance of DBT decreased in the order of TiO2–ZrO2 ≫ TiO2-CeO2 > TiO2 ≈ ZrO2. Introducing simultaneous light irradiation together with an adsorption process using TiO2–ZrO2 can dramatically improve the sulfur uptake by 9-fold (5.2 mg-S/g-A) compared to one-step adsorptive desulfurization (0.6 mg-S/g-A) and by 1.4-fold compared to two-step photo-oxidative desulfurization (3.8 mg-S/g-A). Light and TiO2–ZrO2 play important roles in the LEOADS: Light enhanced peroxide generation and the TiO2–ZrO2 promoted the oxidation of DBT to DBTO2 with the in situ generated peroxide. X-ray diffraction, UV–vis spectroscopy, N2-adsorption desorption, and scanning electron microscopy techniques were used for the characterization of the materials.

Oxidative desulfurization of dibenzothiophene and simultaneous adsorption of products on BiOBr-C3N4/MCM-41 visible-light-driven core–shell nano photocatalyst

In this study, different amounts of BiOBr (x = 0, 5, 10, 15 wt%) and 5% wt. of g-C3N4 were loaded on MCM-41 as core for photo oxidation of DBT and simultaneous adsorption of oxidation products. Among studied photocatalysts, the BiOBr-C3N4/MCM-41 photocatalyst with 10% wt. of BiOBr indicated the highest activity so that this sample reduced DBT concentration to the lowest value of C/C0 = 0.08 after 150 min irradiation of visible light. The characterization of the as prepared photocatalysts by XRD, FESEM, TEM, FTIR, BET-BJH, UV–Vis DRS, and PL analyses revealed that this achievement was due to the highest amount of structural defects and the strongest interaction between BiOBr-C3N4 shell and MCM-41 core in this sample. Moreover, this sample indicated the lowest recombination rate of charge carriers, the narrowest band gap, and high porosity that enhanced the photocatalytic efficiency. However, this sample lost 18% of initial activity after four successive cycles of photo oxidation-adsorption that based on FTIR and BET-BJH was because of plugging of pores by DBT sulfones.

Experimental and theoretical study of deep oxidative desulfurization of Dibenzothiophene using Oxalate-Based catalyst

The present study reports the experimental and theoretical investigation for production of ultra-low sulfur liquid fuels through estimation of various reactive species formed during the reaction with the help of simulation. All the experiments were performed using an ultrasound bath which operates at a frequency of 37 kHz and a theoretical power of 95 W. The presented oxalate-based technique is found to be more efficient with > 93% DBT oxidation within 15 min of reaction time at 25 °C due to formation of reactive species like FeIIC2O4 and FeIIC2O422- which accelerate the reaction kinetics. Moreover, we have also investigated the influence of process parameters such as molar ratio of C2O42-/Fe2 +, oxidant concentration, volume ratio of organic to aqueous phase, sulfur concentration, and activation methods of oxidant. The results revealed that catalyst can be reused for several runs without decrease in catalytic activity. The experimental and simulation of cavitation bubble dynamics results revealed that sonochemical effect assists to accelerate the reaction kinetics through formation of free radicals (•O, •H, •OH and HO2∙) and other reactive species like O3 and H2O2 generated during transient cavitation. The sono-physical effects of cavitation help to create a fine emulsion in the liquid–liquid heterogeneous system leading to enhanced mass transfer rate by providing more interfacial surface area for occurring chemical reaction.

Deep aerobic oxidative desulfurization of model fuel by Anderson-type polyoxometalate catalysts

Anderson-type polyoxometalate (POM) catalysts were synthesized and applied for deep oxidative desulfurization of model fuel containing dibenzothiophene. O2 contained in air was used as oxidant under mild conditions. The influence of the nature of central heteroatom and that of the quaternary ammonium cation used on the conversion of DBT was investigated. For the first time to the best of our knowledge, the role of the solvent in aerobic oxidative desulfurization was investigated and the possible mechanism of DBT oxidation was suggested. It was shown that the key stage in the oxidation of the sulfur-containing compound is the generation of alkyl peroxides from the solvent.

Oxidation of Dibenzothiophene in Water Vapor and Argon at Increased Pressure

This article presents the results of study of dibenzothiophene (DBT, the fuel equivalence ratio $$\varphi = 0.94$$ –1.01) oxidation in a medium of dense water vapor or argon at uniform heating (1 K/min) to 853 K of a tubular reactor made of stainless steel. The oxidation of DBT was found to proceed by the mechanisms of heterogeneous and homogeneous reactions. From the dynamics of the temperature of the reaction mixtures it follows that self-ignition of DBT in an environment of water vapor and argon occurs at 532 K. A Pt-Rh/Pt thermocouple introduced into the center of the reaction volume was found to have a catalytic effect on DBT oxidation. The results of mass spectrometry analysis of gas products show that the degree of carbon burnout exceeds 95% mol. The interaction of stainless steel and H $$_{2}$$ SO $$_{4}$$ formed in the DBT oxidation in water vapor causes steel corrosion, which is suppressed due to neutralization of the acid by calcium carbonate. The composition of the corrosion products was determined by the X-ray diffraction and energy-dispersive analysis methods.

Preparation of vanadium-MFI zeolite for oxidative desulfurization with the aid of ammonium carbonate

Vanadium-MFI zeolites with enhanced vanadium insertion were synthesized through an ammonium carbonate-assisted hydrothermal synthesis and applied as heterogeneous catalyst for the oxidation of organosulfur compounds DBT and 4,6-DMDBT. The prepared vanadium-MFI zeolites were characterized by Scanning electron microscope, Transmission electron microscope, X-ray diffraction, Fourier-transform infrared spectroscopy, UV–vis diffuse reflectance spectroscopy and Raman spectroscopy. The obtained UV–vis spectra disclosed that addition of ammonium carbonate could effectively strengthen the insertion of vanadium element, and on the same time enhance the tetrahedral framework vanadium percentage in vanadium species. The synthesized N-VS(4) zeolite could realize almost complete oxidation of DBT in 240 min, which is obviously better than N-VS(3) and N-VS(5) zeolite. Moreover, the calcined recycled N-VS(4) zeolite shows good re-usability for more than four cycles, which indicates it is an active and stable heterogeneous catalyst.

New mesoporous catalysts with Brønsted acid sites for deep oxidative desulfurization of model fuels

Mesoporous silica of MCM-41 type modified by sulfonic groups and molybdenum atoms has been synthesized. First time was investigated the activity of MCM-41 with chemically immobilized sulfonic groups as oxidative desulfurization catalysts and its activity was compared with molybdenum containing analogs. The main factors affecting the process consisting of catalyst dosage, temperature, reaction time, oxidant dosage were investigated in detail. In optimal conditions dibenzothiophene and 4-methyldibenzothiophene were removed completely. It was shown that nonmetal containing MCM-SO3H is an effective catalyst of oxidation desulfurization even better than molybdenum containing analogs. These catalysts retain their activity in DBT oxidation for 10 cycles.

Catalytic oxidation of DBT for ultra-deep desulfurization under MoO3 modified magnetic catalyst: The comparison influence on various morphologies of MoO3

In this work, deep oxidative desulfurization was attained using a new kind MoO3 modified magnetic catalysts, in which metal organic framework (MOF-199) as supports and the magnetic Fe3O4 added to provide the extra character for increasing practical use value. The characterization of the as-designed catalysts were assessed by FT-IR, XRD, SEM, TPR and XPS analyses. To be noted, various morphologies of MoO3 were used to form the final products and compared to discuss their influences on the ODS performance in this work. Among them, the Fe@Mo-4@MOF, containing the fibroid MoO3, showed an excellent catalytic performance to the ultra-deep oxidative desulfurization in 45 min, which was mainly attributed to the special morphology of MoO3, providing the higher contact area with the DBT to increase the ODS efficiency. Moreover, the possible mechanism was proposed to illustrate the ODS process and only slight decrease of DBT removal was observed after 15 recycling times.

Iron and molybdenum mixed oxide supported on Al-PILC for the catalytic oxidative desulfurization of dibenzothiophene in simulated diesel fuel.

In this work, three novel catalysts were prepared by 2.5, 5.0, and 10.0wt.% facile impregnation with an iron and molybdenum mixed oxide (Fe/Mo) on an aluminum pillared clay (Al-PILC) support. These materials were characterized by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), temperature programed reduction (TPR), and nitrogen (N2) physisorption at 77K. Characterizations indicated that the metal particles were dispersed on the surface of the three catalysts, and the interlayer d001 spacing of the pillared material remained unchanged after the impregnation process. The catalytic tests showed good results for DBT oxidation using the synthesized catalysts, with high turnover frequency (TOF) values, particularly for the material with 5.0wt.% Fe/Mo. Theoretical calculations were carried out at the density functional theory (DFT) level, to investigate how the DBT molecules were adsorbed onto the surface of the mixed oxide. The lowest energy proposal was obtained when both Fe and Mo were present at the active sites, indicating a possible synergistic effect of the metals on catalyst activity. Reuse tests indicated that the catalysts could be employed effectively for up to 3cycles in a row, then a decrease in activity occurred and the active sites needed to be regenerated.

MoWFe based catalysts to the oxidative desulfurization of refractory dibenzothiophene compounds: Fe promoting the catalytic performance

The oxidative desulfurization (ODS) process is a potential technology to complement the actual hydrodesulfurization process to reach the ultra-low sulfur level in diesel fuels. In this work, oxides of MoWFe based catalysts (totally calcined and partially reduced) were prepared and tested in the ODS process to study the promoting effect of Fe species on the catalytic activity and the interactions between Mo, W and Fe. γ-Al2O3 was used as catalytic support and H2O2 as oxidant agent. The catalysts were characterized by temperature programmed reduction (TPR), scanning electron microscopy (SEM-EDX), X-ray diffraction (XRD) and N2-physisorption. The characterization results shown a synergetic effect between Mo and W that improve the catalytic activity. Also, it was observed a promoting effect of Fe on W and Mo species improving the distribution of high-interaction Mo species and low-interaction W species which enhanced the ODS activity. The catalytic activity of MoWFe catalysts was higher than monometallic and bimetallic catalysts. It was reached the complete oxidation of DBT, 4-MDBT and 4,6-DMDBT in a simplified ODS system and a removal of 98% of sulfur compounds in a three-phase extraction-oxidation system.

Ce/Al2O3 as an efficient catalyst for oxidative desulfurization of liquid fuel

Present paper evaluates the catalytic activity of Ce/Al2O3 (CeAl) catalyst for the oxidative removal of sulfur from model oil (dibenzothiophene, DBT, dissolved in iso-octane). CeAl catalyst synthesized using wetness impregnation technique was characterized by various techniques like Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Thermo gravimetric and Brauner- Emmett-Teller (BET) surface area. CeAl catalyst was further used as catalyst for the optimization of operating parameters. Optimum dose was found to be 10 g/l. The catalytic oxidation of DBT was found to be gradual process with optimum reaction time of 3 h at mild conditions (atmosphere pressure and 60 °C).