Catalyst For Oxidative Desulfurization Research Articles

Sequential Post-Synthetic Modification and Evaluation of Catalytic Activity of Hierarchically Porous Sulfated Geopolymer in the Oxidative Desulfurization of Dibenzothiophene

A novel sulfated hierarchically porous geopolymer catalyst for the oxidation of dibenzothiophene was prepared through sequential treatment with desilication, ion-exchange and sulfation techniques. Desilication and ion-exchange treatments were aimed at the creation of hierarchical porosity and controlling the surface area of the geopolymer, while sulfation treatment was primarily done to enhance the acidity of the hierarchically porous geopolymer. The properties of the catalyst obtained after the modifications was studied by BET, NH3-TPD, SEM, TEM, XRD, FTIR and XRF analyses. As a result of the proposed sequential treatment, the activity of the geopolymer towards the oxidation of dibenzothiophene was profoundly increased and reflected in the enhanced conversion from 14 to 85%. A plausible electronic mechanism proposed for the reaction accentuated that the reaction might take place in two stages: the formation of sulfated geopolymer peroxo complex as the active catalyst and nucleophilic attack by dibenzothiophene over the peroxo complex to form the product, both were elaborated with suitable kinetic model. The interaction between dibenzothiophene and peroxo complex was considered to be of primary concern, based on which, Langmuir–Hinshelwood kinetic model was developed. Effective regeneration upto three cycles emphasized its potential to be exploited as an efficient catalyst for oxidative desulfurization.

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.

An Effective Magnetic Catalyst for Oxidative Desulfurization of Model and Real Fuels: Fe3O4/ZIF-8/TiO₂

In the current research, an advanced and innovative composite based in zeolitic imidazolate framework-8 (ZIF-8) incorporating magnetic and effective oxidative catalytic properties was successfully used to prepare ultra-low sulfur model and real fuels by oxidative desulfurization (ODS) process. To this purpose, the surface of ZIF-8 was decorated by TiO 2 and Fe 3 O 4 nanoparticles (NPs) to prepare the composite catalyst (Fe₃O₄/ZIF-8/TiO₂). Structural characterization was performed by XRD, FT-IR, SEM, EDS, TEM, N 2 adsorption-desorption isotherm and VSM. TEM images showed that the semi-spherical TiO 2 and Fe 3 O 4 NPs are fairly doped. The effect of TiO 2 and Fe 3 O 4 NPs incorporated in ZIF-8 support allowed an efficient catalytic oxidative desulfurization of model fuel (500 ppm of dibenzothiophene, DBT) and real fuels (gasoline, diesel, among others) using tert-Butyl hydroperoxide (TBHP) as oxidant under a solvent-free system. Optimization studies were performed and complete desulfurization of model fuel was found after 6 h using O/S = 3 at 80 °C, instead of the 33% of desulfurization obtained with the pristine ZIF-8. Under optimized conditions, sulfone was the only product observed. The stability and the recycle capacity of the Fe₃O₄/ZIF-8/TiO₂ composite catalyst was confirmed and after ten consecutive ODS cycles only a slight decrease of desulfurization efficiency was detected (around 10%). Therefore, the results here presented confirm that the magnetic catalyst conciliates efficiency, stability and easy recovery, that are essential properties for future industrial application. • Magnetic catalytic composite has been prepared based on ZiF-8 support. • Fe 3 O 4 /ZIF-8/TiO 2 presents high catalytic efficiency for oxidative desulfurization of model and real fuels. • Solvent-free oxidative catalytic system was successfully used. • Complete desulfurization was achieved after 6 h using O/S = 3. • Catalyst presented high stability and recycle capacity for 10 consecutive desulfurization cycles.

Molybdenum nitride@porous carbon, derived from phosphomolybdic acid loaded metal-azolate framework-6: A highly effective catalyst for oxidative desulfurization

A new composite of the metal-azolate framework (MAF-6) and phosphomolybdic acid (PMA), named PMA(x)@MAF-6, was prepared. Well-dispersed (size: ∼4 nm) Mo2N, on porous carbon, was prepared without external nitrogen sources firstly via carbonization of the PMA(x)@MAF-6. The prepared catalyst was applied in oxidative desulfurization (ODS) with H2O2 as a greenoxidant and showed remarkable performance. A selected catalyst Mo2N@C-3 had the highest turnover frequency (30 h-1, around 2–3 times of the best catalyst so far) with the lowest activation energy (27.8 kJ·mol−1) in ODS (with H2O2) among any molybdenum-based catalysts. The ODS over Mo2N@C was explained by a non-radical mechanism via active Mo-peroxo species. Moreover, the high activity of the catalyst is partly because of the contribution of nitrogen in Mo2N. The studied catalyst could be easily recycled by solvent washing. Therefore, Mo2N, especially supported on carbon (like Mo2N@C), could be firstly suggested as a promising catalyst in ODS.

Natural clay nanotube supported Mo and W catalysts for exhaustive oxidative desulfurization of model fuels

Abstract Oxidative desulfurization is a promising way to produce, under mild conditions, clean ecological fuels with ultra-low sulfur content. Herein, we present for the first time heterogeneous catalysts based on natural aluminosilicate nanotubes (halloysite) loaded with transition metal oxides for oxidative sulfur removal using hydrogen peroxide as environmentally safe oxidant. The halloysite nanotubes (HNTs) provide acid sites for C–S bond scission, while the Mo and W oxides act as hydrogen peroxide activators. The structure and acidity of both the clay support and catalysts were investigated by low-temperature nitrogen adsorption/desorption, Fourier-transform infrared spectroscopy, X-ray fluorescence analysis, and transmission electron microscopy techniques. These clay-based catalysts revealed the high activity in the oxidation of various classes of sulfur-containing compounds (sulfides, heteroatomic sulfur compounds) under mild reaction conditions. The conversion of various substrates decreases in the following trend: MeSPh > Bn2S > DBT > 4-MeDBT > BT, which deals with substrate electron density and steric hindrance. The influence of the temperature, oxidant to sulfur molar ratio, and reaction time on catalytic behavior was evaluated for Mo- and W-containing systems with various metal content. The complete oxidation of the most intractable dibenzothiophene to the corresponding sulfone was achieved at 80 °C and H2O2:S = 6:1 (molar) for 2 h both for Mo- and W-containing systems. These transition metal oxides HNTs supported catalysts are stable for 10 cycles of dibenzothiophene oxidation, which makes them promising systems for clean fuel production.

Construction of bifunctional 3-D ordered mesoporous catalyst for oxidative desulfurization

The development of catalysts with the functions of catalyzing the oxidation of organosulfur and separating the products from reaction mixturesis facilitates to achieve high-efficiency oxidative desulfurization (ODS) of fuel. Herein, the MoO3 nanoparticles (mean diameter = 1.33 nm) confined in Ti-doped KIT-6 could be synthesized by triblock copolymer (EO20PO70EO20)-assisted in-situ synthesis method combined with stepwise pyrolysis. The prepared catalyst (Mo/KIT-6-Ti) exhibited excellent ODS performance. When cumene hydroperoxide (CHP) was used as the oxidant, Mo/KIT-6-Ti not only could completely remove dibenzothiophene (DBT) in the model gasoline at room temperature in 40 min but also had the excellent ability to adsorb and separate the sulfone product from the model gasoline. After five reaction-regeneration cycles, the DBT conversion over Mo/KIT-6-Ti still reached above 99% in 60 min. Furthermore, kinetic studies revealed that the oxidation reaction of DBT on Mo/KIT-6-Ti had extremely low activation energy (34.9 kJ/mol). Data from radical scavenger experiments suggested that hydroxyl radicals play a dominant role in the ODS. This catalyst has the potential to negate the need for a solvent extraction step in fuel desulfurization and produce ultralow sulfur fuel.

Ti-grafted MIL-101 as hydrophilic catalyst for efficient oxidative desulfurization of dibenzothiophene with hydrogen peroxide

Ti-containing porous materials are extensively studied in liquid-phase oxidative desulfurization (ODS) to obtain low-sulphur fuel, these materials displayed excellent ODS performance co-operating with organic oxidants but relatively poor ability with H2O2, which is a green and cheap oxidant widely used in industrial process. To overcome this challenge, we reported a H2O2 compatible ODS catalyst Ti-MIL-101 by treating MIL-101 with TiCl4 in dehydrated CH2Cl2. The results of N2-absorption, UV–vis, IR and XPS indicated that Ti species were mainly confined in mesopore cages of MIL-101 in the form of isolated and oligomeric octahedral Ti which were grafted to Cr centres of MIL-101 by Cl bridge. Moreover, wettability studies further suggested this catalyst possessed good affinity with water-based substance. As a result, Ti-MIL-101 exhibited efficient ODS ability in the oxidative reaction of DBT with H2O2 compared with that with organic oxidant. In model fuel, sulphur content was reduced to less than 10 ppmw from 1000 ppmw within 30 min at 333 K and the corresponding TOF value over Ti-MIL-101 reached 16.8 h−1. This outstanding catalytic ability might be the result of the synergy between the distinct active Ti species and the good surface affinity of Ti-MIL-101. Ti-containing metal–organic frameworks were prepared for oxidative desulfurization of obstinate sulphur compounds with H2O2. This catalyst displayed highly efficient activity in ODS of DBT. The sulphur content was reduced from 1000 ppmw to less than 10 ppmw in 30 min, corresponding TOF number reached 16.8 h−1. This outstanding catalytic result could be attributed to the superior affinity between catalyst and oxidant.

Triphenyl methyl phosphonium tosylate as an efficient phase transfer catalyst for ultrasound-assisted oxidative desulfurization of liquid fuel.

The novel phosphonium-based ionic liquid (IL), triphenyl methyl phosphonium tosylate ([TPMP][Tos]), has been synthesized and applied as a phase transfer catalyst (PTC) in the ultrasound-assisted oxidative desulfurization (UAODS). Oxidation of model fuel (MF) containing dibenzothiophene (DBT) was carried out using an equimolar mixture of H2O2-CH3COOH as an oxidant at 40-70 °C in the presence of IL. The sulfur compound is converted into polar sulfone, and the maximum desulfurization efficiency was examined. The effect of process parameters such as reaction temperature, reaction time, molar ratio of oxidant to sulfur (n(O/S)), and the mass ratio of ionic liquid to model fuel (m(IL/MF)) was studied, and the conditions for maximizing the DBT conversion rate were found. Maximum conversion (> 99%) was obtained at a temperature of 70 °C with m(IL/MF) of 0.8. The oxidation reactivity of various sulfur compounds was studied at different time intervals. To verify the effect of ionic liquid and ultrasound irradiation, extractive desulfurization (EDS), oxidative desulfurization (ODS), and UAODS in the presence of IL were carried out. The experimental results show that the UAODS process gives the highest desulfurization efficiency. A kinetic study was performed to estimate the rate constant and the order of oxidation reaction.

Enrichment of polymeric WOx species in WOx@SnO2 catalysts for ultra-deep oxidative desulfurization of liquid fuels

Designing an efficient and selective catalyst for the ultra-deep sulfur removal from liquid fuels under mild conditions is vibrant in environmental catalysis. This work reports the preparation of catalysts, i.e., WOx-based active sites generated on SnO2, for the sulfur removal from model diesel via biphasic oxidative desulfurization (ODS). The different active species generated on SnO2 such as monomeric and polymeric WOx species, and crystalline WO3 are characterized. Besides being the support, SnO2 adsorbs the sulfur compounds from the oil phase and boosts the ODS performance. No significant change in the ODS activity of WOx@SnO2 is observed in the presence of intrusive nitrogen and aromatic compounds. The order of ODS activity towards different sulfur compounds is dibenzothiophene (DBT) > 4,6-dimethyl DBT > benzothiophene. While using SnO2 with a higher surface area (96.5 m2/g) instead of that with a lower surface area (19.2 m2/g), the formation of highly efficient polymeric WOx species is enhanced. Consequently, the turn over frequency is augmented from 10.99 to 43.23 h−1, which is closely a 4-fold increase. The polymeric WOx species produced on SnO2 having the higher surface area are visualized by HAADF-STEM analysis. Scalable preparation and the higher turnover frequency of the present catalyst can develop a promising catalytic system for the ODS.

Synthesis, Characteristic and Application of PAM Catalysts for Oxidative Desulfurization

Oxidative desulfurization has been widely used in the desulfurization process for petroleum production. But conventional oxidative desulfurization catalyst was low desulfurization efficiency, low recycle use, and the mechanism was unclear. In this work, polyacrylamide (PAM) was first used in the loading of heteropolyacids and was used in oxidative desulfurization, which was prepared by simple reaction of each of the heteropolyacids and PAM. The optimal process condition for the catalyst was chosen by the single factor experiment. The optimal condition was as follows: the temperature was 60°C, the amount of the catalyst was 0.2 g, the oxygen to sulfur ratio was 16, and the reaction time is 100 minutes. Besides, the cycle use experiment indicated the desulfurization efficiency was high after 10 times. In the end, the oxidative desulfurization mechanism was put forward. The catalyst had a good industrial development prospect.

The optimization of preparation mode of metal-carbon catalysts for oxidative desulfurization of diesel fractions

To create new nanosized catalysts for oxidative transformations of sulfur compounds of thiophene series, monometallic catalysts based on carbon nanotubes M/CNTs (M = Ce, Cu, Mo) were prepared with a variation of the synthesis method. The incipient wetness impregnation method, adsorption, and precipitation methods were applied for active component introduction onto CNTs. The effect of preparation mode on textural and structural characteristics of M/CNTs was investigated using a set of physicochemical methods (optical emission spectrometry with inductively coupled plasma, low-temperature nitrogen adsorption, X-ray phase analysis, Raman spectroscopy, and scanning electron microscopy). It was shown that precipitation and impregnation methods provide appropriate metal content in catalyst composition while adsorption is suitable for synthesizing samples with a low active component concentration. The kinds of active component species are similar (CeO2, Cu2O/Cu or MoO3/MoO2) but their distribution behavior and dispersion are controlled by the preparation mode. The using precipitation method for M/CNTs synthesis provides uniform distribution of the nanosized metal-containing particles on the carbon matrix surface.

Efficient and reusable ordered mesoporous WO x /SnO2 catalyst for oxidative desulfurization of dibenzothiophene.

The oxidative desulfurization (ODS) of organic sulfur compounds over tungsten oxide supported on highly ordered mesoporous SnO2 (WOx/meso-SnO2) was investigated. A series of WOx/meso-SnO2 with WOx contents from 10 wt% to 30 wt%, were prepared by conventional wet impregnation. The physico-chemical properties of the WOx/meso-SnO2 catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption isotherms, electron microscopy, Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, and the temperature-programmed reduction of hydrogen (H2-TPR). The characterization results indicated that these catalysts possessed mesoporous structures with uniform pores, high specific surface areas, and well-dispersed polyoxotungstate species on the surface of meso-SnO2 support. The ODS performances were evaluated in a biphasic system (model oil/acetonitrile, Sinitial = 2000 ppm), using H2O2 as an oxidant, and acetonitrile as an extractant. Dibenzothiophene (DBT) in the model oil was removed completely within 60 min at 50 °C using 20 wt% WOx/meso-SnO2 catalyst. Additionally, the effect of reaction temperature, H2O2/DBT molar ratio, amount of catalyst and different sulfur-containing substrates on the catalytic performances were also investigated in detail. More importantly, the 20 wt% WOx/meso-SnO2 catalyst exhibited 100% surfur-removal efficiency without any regeneration process, even after six times recycling.

Ligand Modified Metal Organic Framework UiO-66: A Highly Efficient and Stable Catalyst for Oxidative Desulfurization

It is reported that the UiO-66(Zr) material could catalyze oxidative desulfurization (ODS) reaction, but its stability is inferior. In this work, a family of functionalized UiO-66(Zr) with different groups (–NH2, –NO2, –Br) were prepared to enhance this material’s activity and stability. Characterizations and ODS tests show that the groups have profound influence over the physicochemical properties of UiO-66(Zr). Among functionalized UiO-66(Zr), UiO-66(Zr)-NO2 exhibited the best ODS activity, their ODS performance is linear correction with their Hammett values. Recycling experiments indicate UiO-66(Zr)-NO2 has no deactivation.

Enhancement of catalytic performance over MOF-808(Zr) by acid treatment for oxidative desulfurization of dibenzothiophene

The development of active oxidative desulfurization (ODS) catalysts is of practical importance. Recently, MOF-808(Zr) has been attempted to use as ODS catalyst due to its various advantages. However, generally MOF-808(Zr) prepared by conventional method was less active in the oxidation reactions due to the lack of defect sites in the structure. In this contribution, we report that the catalytic oxidative performance of MOF-808(Zr) can be enhanced by acid treatment due to the formation of defect sites resulting from the partial removal of organic linkers in the structure. During the experiment, the effect of acid concentration, treatment time, the addition amount of oxidant and reaction parameters on the performance of MOF-808(Zr) was studied. The catalytic results show that MOF-808(Zr) treated with 0.4 M HCl for 1h can catalyze the oxidation of dibenzothiophene completely at 60°C in 15 min. The activity (mole number of converted DBT per hour per unit mass) is 70 mmol h−1 g−1, which is much higher than that (45 mmol h−1 g−1) of parent MOF-808(Zr). In addition, the catalyst can be reused several times without obvious loss of catalytic performance.

The encapsulation of POM clusters into MIL-101(Cr) at molecular level: LaW10O36@MIL-101(Cr), an efficient catalyst for oxidative desulfurization

The anchoring of Weakley-type polyoxometalate (POM) Na 7 [H 2 LaW 10 O 36 ] in mesoporous metal-organic framework (MOF) MIL-101(Cr) to prepare a novel host-guest composite is here reported for the first time. The successful encapsulation of LaW 10 into MIL-101(Cr) has been achieved via facile tandem post-synthetic modification strategy and confirmed by several instrumental techniques. The LaW 10 guests were dispersed homogeneously in MIL-101(Cr) nanocages at molecular level. The as-synthesized composite combines both the merits of the POMs (remarkable efficiency and reversible redox) and MOF (sufficient recyclability and exceptional porosity), thus displaying obvious host-guest synergistic effect. The LaW 10 O 36 @MIL-101(Cr) composite served as heterogeneous single-site catalyst for ODS process and exhibited excellent catalytic performance, with removal efficiency of 99.1, 94.5 and 84.7% for DBT, 4,6-DMDBT and BT, respectively. Thanks to the confinement effect from Cr···O W coordinative interaction, the catalyst provided outstanding recyclability and stability, and can be reused for seven times without leaching, structural alteration and deactivation. Moreover, the structure-activity relationship was investigated in detail, as well as the proposed mechanism. • The Weakley structure POMs were encapsulated into MIL-101(Cr) for the first time. • The LaW 10 O 36 were dispersed uniformly within MIL-101(Cr) at molecular level. • The host-guest synergistic effect enhanced remarkably ODS efficiency and durability. • The confinement effect of MIL-101(Cr) on LaW 10 O 36 results in excellent ODS recyclability.

Phosphomolybdic acid niched in the metal-organic framework UiO-66 with defects: An efficient and stable catalyst for oxidative desulfurization

The synthesis of highly efficient and stable catalysts for oxidative desulfurization is still a challenging task. Herein, a composite material (HPMo@UiO-66) of phosphomolybdic acid (HPMo) encapsulated in the metal-organic framework UiO-66 with missing-linker defects was prepared via a one-pot hydrothermal method. A series of as-synthesized catalysts were systematically characterized by XRD, FT-IR, SEM, BET, TGA, XPS, UV–vis and PL. Through oxidative desulfurization experimental evaluations, the catalyst 0.5-HPMo@UiO-66-D with defects shows the superior catalytic oxidative desulfurization performance and high reusability. 0.5-HPMo@UiO-66-D is able to completely remove DBT in the model fuel in 60 min, and the reaction system can be recycled 10 times with a high activity. In addition, the kinetics and the activation energy of the oxidative desulfurization were studied.

PMo12@UiO-67 nanocomposite as a novel non-leaching catalyst with enhanced performance durability for sulfur removal from liquid fuels with exceptionally diluted oxidant

In the present study, Keggin-type phosphomolybdic acid (H3PMo12O40) was encapsulated in a sized-matched Zirconium metal-organic framework (PMo12@UiO-67) to be used as a heterogeneous catalyst for oxidative desulfurization. A proper cage size and narrow window of UiO-67 were exploited to avoid the phosphomolybdic acid leaching to provide a suitable platform for a majority of the sulfur compounds. The prepared composite demonstrated remarkable catalytic activity for ultra-deep oxidative desulfurization of 5 sulfur compounds under mild conditions. 37.50 ppm sulfur remained in the oil after 20 min and no sulfur compounds were detected after 30 min. The trapping experiments indicated no contribution of the radical scavenger to the desulfurization activity. Also, it could be concluded that PMo12@UiO-67 can be readily regenerated and recycled for 6 successive cycles with no considerable loss of catalytic activities.

Few Layer g-C3N4 Dispersed Quaternary Phosphonium Ionic Liquid for Highly Efficient Catalytic Oxidative Desulfurization of Fuel

Functionalized ionic liquids (ILs) have been considered as efficient catalysts for oxidative desulfurization (ODS), but the further industrial applications are hampered by the poor separability wit...

Titanium-Modified MIL-101(Cr) Derived Titanium-Chromium-Oxide as Highly Efficient Oxidative Desulfurization Catalyst

A titanium-chromium-oxide catalyst was prepared by a facile calcination of titanium-modified MIL-101(Cr). The resulting material, possessing a surface area of 60 m2 g−1 and a titania content of 50.0 wt%, can be directly used as the catalyst for oxidative desulfurization (ODS) reaction of dibenzothiophene (DBT). This novel ODS catalyst can remove 900 ppm sulfur-containing compounds in a reaction time of 30 min at 60 °C. The experimental results showed that the specific activity increased with the titanium content. The specific activity of the catalyst with 50%Ti reached 129 μmol/m2, which was much higher than that of reported Ti-based catalysts.

Iron Oxide Catalyst for Oxidative Desulfurization of Model Diesel Fuel

— The catalytic oxidative desulfurization (Cat-ODS) process has been introduced as a new technology to achieve ultra-low sulphur levels in diesel fuels. In this study, the performance of the alumina supported iron oxide based catalysts doped with cobalt, synthesized via wet impregnation method on the Cat-ODS of the model diesel with the total sulphur 500ppm was investigated using tert-butyl hydroperoxide (TBHP) as an oxidizing agent and N,N-dimethylformamide as an extraction solvent. A series of dopant was being screened. Co/Fe-Al2O3 (10:90) and Co/Fe-Al2O3 (20:80) prepared at 400°C. Overall, the catalytic activity decreased as dopant ratio increased. Catalyst with 10 wt% of Co was successfully removed 96% of thiophene, 100% of DBT and 92% of 4,6-DMDBT in model diesel. Further investigation, potential catalyst that calcined at 400°C contributed higher sulphur removal compared to the catalyst calcined at 500°C. X-ray diffraction analysis (XRD) result showed that Co/Fe-Al2O3 (10:90) prepared at 400°C was amorphous, while micrograph of the field emission scanning electron microscopy (FESEM) illustrated an inhomogeneous distribution of various particle sizes. The energy dispersive X-ray analysis (EDX) result have confirmed the presence of Fe and Co in all of the prepared catalyst.