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Ti/TiO2/NiWO4 + WO3 composites for oxidative desulfurization and denitrogenation
Abstract
The catalytic properties of Ti/TiO2/NiWO4 + WO3 composites fabricated by plasma electrolytic oxidation (PEO) of titanium in a solution containing 0.1 mol/L Na2WO4 + 0.1 mol/L CH3COOH + 0.05 mol/L Ni(CH3COO)2 were studied in model reactions of peroxide oxidation of thiophene (T), dibenzothiophene (DBT), methylphenyl sulfide (MPhS), and pyridine (Py). This paper demonstrates for the first time that such composites are promising for catalytic oxidation of both S-containing and N-containing petroleum compounds. By the example of the reaction of dibenzothiophene oxidation, the optimal reaction temperature (60 °C) and the content of hydrogen peroxide in the reaction mixture were established, and the efficiencies of the Ti/TiO2/NiWO4 + WO3 and Ti/TiO2/WO3 composites were compared to show the role of nickel in increasing their activity and stability. It was found that, with respect to organosulfur substrates, the activity of the Ti/TiO2/NiWO4 + WO3 catalyst decreases in the series: methylphenyl sulfide > dibenzothiophene > thiophene. The changes in surface morphology and elemental composition of composites after catalytic tests have been evaluated using SEM, EDS and XPS. It has been established that the use of the Ti/TiO2/NiWO4 + WO3 catalyst makes it possible to achieve a deep degree of desulfurization of the diesel fraction of petroleum feedstock (>90%).
... The reactivity of PEO layers can be easily influenced by changing the composition of the electrolytic bath, which is usually completed by adding soluble ions of dopants, i.e., Ni and Cu, to the electrolytic bath to prepare catalytic materials for CO to CO 2 oxidation [27][28][29], photoactive materials [26,30,31], biomaterials with possible antibacterial properties [32,33] or even catalysts for desulphurization and denitrification [34]. Other methods of doping of PEO layers are the impregnation of the coating with the soluble salt of the dopant, followed by drying and air annealing (500-1050 • C) [29,[35][36][37][38][39][40][41][42], the hydrothermal route [43,44], electrodeposition [45,46], the sol-gel method [47], electroless plating [48], the solid-state reaction method [49], the alcohol-thermal method [50], reactive magnetron co-sputtering [51], dip coating [52] or even the coating of different materials with a TiO 2 paste [53]. ...
... A similar electrolytic bath, based on silicates, resulted in the preparation of an oxide layer with an average thickness of 13 μm [40], which is almost three times thinner than in our case. Similar values were observed for a phosphate-based solution, with an average thickness of 13.1 μm [63], for an acetic acid-based solution with the addition of nickel acetate, with a value of 12 μm [34], and for a H3PO4-based solution with the addition of copper nitrate with a value of 27.8 μm [33]. Depending on the process conditions, the oxide layers prepared in PBW (Na3PO4 + Na2B4O7 + Na2WO4) electrolytes containing Ni and Cu were thinner (10-14 μm) [28,35], similar (40 μm) [29] or even thicker after the addition of sodium silicate to the electrolytic bath (53.5 μm) [39]. ...
... A similar electrolytic bath, based on silicates, resulted in the preparation of an oxide layer with an average thickness of 13 µm [40], which is almost three times thinner than in our case. Similar values were observed for a phosphate-based solution, with an average thickness of 13.1 µm [63], for an acetic acid-based solution with the addition of nickel acetate, with a value of 12 µm [34], and for a H 3 PO 4 -based solution with the addition of copper nitrate with a value of 27.8 µm [33]. Depending on the process conditions, the oxide layers prepared in PBW (Na 3 PO 4 + Na 2 B 4 O 7 + Na 2 WO 4 ) electrolytes containing Ni and Cu were thinner (10-14 µm) [28,35], similar (40 µm) [29] or even thicker after the addition of sodium silicate to the electrolytic bath (53.5 µm) [39]. ...
The increasing climate crisis requires an improvement in renewable energy technologies. One of them are fuel cells, devices that are capable of generating electricity directly from the chemical reaction that is taking place inside of them. Despite the advantages of these solutions, a lack of the appropriate materials is holding them back from commercialization. This research shows preliminary results from a simple way to prepare black TiO2 coatings, doped with Cu or Ni using the plasma electrolytic oxidation process, which can be used as anodes in urea-fueled fuel cells. They show activity toward urea oxidation, with a maximum current density of 130 μA cm−2 (@1 V vs. Hg|HgO) observed for Cu-enhanced TiO2 and low potential of only 0.742 V (Vs Hg|HgO) required for 50 μA cm−2 for Ni-enhanced TiO2. These results demonstrate how the PEO process can be used for the preparation of TiO2-based doped materials with electrocatalytic properties toward urea electrooxidation.
... Titanium catalysts such as TiO 2 @porous carbon and TiN@nitrogen enriched porous carbon have demonstrated high efficiency for the oxidation of neutral indoles but are slightly ineffective towards the oxidation of basic NCCs [7,8]. Incorporating tungsten and nickel in titanium-based catalysts have been reported to facilitate the oxidation of basic thiophenes and pyridines without altering their efficacy towards the oxidation of neutral indoles and pyrroles [1,9]. The activity of some zeolite-based catalysts towards the oxidation of nitrogen heterocycles has also been explored [10][11][12]. ...
... As shown in Fig. 7c, the conversion increased with an increase in the O:N from 2 to 14 but declined afterward. The requirement of high amounts of the oxidant can be attributed to three factors, (i) accelerated rate of decomposition of H 2 O 2 into free radicals, (ii) formation of a liquid film of H 2 O 2 over the catalyst surface, and (iii) blocking of the active centers of the catalyst by the water molecules generated from H 2 O 2 decomposition [9,52,53]. The proposed reaction pathway suggests that the reaction occurred via the peroxo pathway, confirming that the short-lived free radicals generated via homolytic cleavage did not participate in the reaction [53]. ...
A hierarchically porous sulfated geopolymer catalyst was prepared by three staged sequential treatments involving desilication, ion exchange, and sulfation steps. The first step helped generate hierarchical porosity through the selective removal of Si. The desilicated geopolymer was converted from basic Na-form to acidic H-form through ion exchange with ammonium chloride solution. The ion-exchanged geopolymer was then impregnated with sulfuric acid to produce a super-acidic sulfated geopolymer catalyst. The physicochemical characteristics of the catalyst were analyzed by XRD, FE-SEM, TEM, BET, XPS, NH3-TPD, and FTIR analysis. Three types of model fuels containing pyridine, indole, and carbazole were prepared to evaluate the performance of the catalyst. The influence of parameters affecting the oxidation of pyridine was assessed by conducting the reaction with varying amounts of catalyst, stirring speed, oxidant to nitrogen ratio, temperature, and initial nitrogen concentration. The reaction proceeded via nucleophilic attack by pyridine on the catalyst and followed pseudo first-order kinetics with a TOF and TON of 22.4 h⁻¹ and 134.4, respectively. The oxidized products were removed from the model oil by extraction with aqueous solvents, and the effect of influencing parameters on the extraction efficiency was also studied. The efficiency of the coupled oxidation-extraction process for the three model fuels varied in the order: pyridine > indole > carbazole.
Graphical Abstract
... An analysis of the literature shows that the most active systems for ODS are formed on the basis of derivatives of W, Mo, and V. Phosphorus often has a promoting effect, since the formation of phosphates affects the structural features of polyoxometalates [17]. Previously, we showed that compositions based on mixed oxides of W with Zn, Mn, Ni, and Ti obtained by plasma electrolytic oxidation (PEO) are active catalysts for the oxidation of S-and N-containing compounds [18,19]. PEO-systems based on molybdenum and vanadium compounds have not yet been studied in these reactions. ...
... Tungsten oxides-based metal catalysts have significant importance due to easy synthesis, low toxicity, cheap cost, and consistent multifunctional performance. 21 The active components are frequently put on supports to improve the activity and separation of the catalysts. Silica, alumina, activated carbon, zeolite, carbon nitride (g-C 3 N 4 ), and other supports have all been studied. ...
The catalysts utilized for oxidative desulfurization have acquired significant attention and ability to improve the quality of the fuel oil by removing sulfur. In this work, the catalysts used for oxidative desulfurization include CoWO 4 and Bi 2 WO 6 with graphitic carbon nitride (g-C 3 N 4 ) as support were synthesized by the one-pot hydrothermal method. Graphitic carbon nitride was obtained by thermal polycondensation of melamine at 550°C for 5 h. These catalysts were homogeneously dispersed on the surface of the support and their structure, morphology, and properties were determined by different characterization techniques (Powder X-Ray Diffractometer, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy and Energy Dispersive X-Ray Spectroscopy, Specific Surface Area (Brunauer, Emmett and Teller (SBET)). The parameters that affect the efficiency of the desulfurization process such as catalyst amount, amount of oxidizing agent, and reaction temperature have been optimized thoroughly. The oxidative desulfurization reaction was studied in terms of kinetics which shows that reaction is pseudo first order. The thermodynamic studies revealed that the reaction is endothermic and spontaneous in nature. The results determined that the catalytic efficiency for the removal of sulfur (as dibenzothiophene) is more than 90% in the presence of support (g-C 3 N 4 ) to obtain sulfur free fuel.
An as-synthesized recyclable Al-NDC@GO composite exhibited remarkable adsorption capacity and high selectivity for pyridine, quinoline and indole.
As sulfur compounds produced by the combustion of fossil fuels are one of the main elements in air pollution, some strict legislation has been issued that specifies the sulfur ratios of different fuels. Therefore, periodic mesoporous organosilicas (PMO) composed of 1,3- bis(trimethoxysilylpropyl)imidazolium chloride ionic liquid, 1,2- bis(trimethoxysilyl)ethane, and phosphotungstic acid or permanganate as counter ions of imidazolium moieties in the framework of PMO-IL were fabricated to obtain highly reactive -MnO4 or -HPW12O40 based heterogeneous catalysts. The synthesized materials were characterized by FT-IR, N2 adsorption–desorption, low and wide-XRD, XPS, TGA, and HRTEM. The surface area was of 615, 425 and 347 m² g–1 for PMO-IL, HPW12O40–PMO-IL and MnO4- PMO-IL, respectively. The desulfurization was studied on three types of aromatic sulfur models. The results revealed that MnO4-PMO-IL and HPW12O40– PMO-IL outperform other catalysts in the oxidative desulfurization process of three kinds of aromatic sulfur compounds; comprising benzothiophene, dibenzothiophene, and 4, 6-dimethyldibenzothiophene even at smaller O/S ratio. The MnO4–PMO-IL catalyst showed the maximum efficiency in reducing sulfur at 50 °C, as it achieved sulfur reduction rates of 93.2, 92.7, and 98.8% after 90 min, while the HPW12O40– PMO-IL catalyst showed a reduction of sulfur by 85.1, 94.3 and 98% after 120 min for BT, DBT, and 4,6-DMDBT compounds, respectively. The two catalysts can be suggested as effective catalysts for oxidative desulfurization of fuel. Furthermore, our research showed that the catalyst might be retrieved and reused at least nine times without a noticeable loss in performance.
The plasma electrolytic oxidation is an innovative method for the surface treatment of titanium and its alloys. This review provides an overview of the historical development of the process and summarizes the current state of the art. The chemical as well as the electro- and plasma-chemical basics of the layer forming mechanisms, which comprises the substrate/electrolyte interface before discharge initiation and the different types and stages of plasma electrolytic discharge phenomena are explained within the context of titanium-based materials. How these phenomena can be influenced by the use of suitable electrolytes and controlled by the electrical regime is described. Subsequently, the microstructures and composition of the layers are described in detail, and the properties for specific applications are then discussed. The resistance of a PEO coating to corrosive environments, tribological factors, and alternating mechanical stress is viewed critically, and the extensive functional properties such as physiological compatibility, photocatalytic activity, and decorative properties are revealed. Finally, examples of various practical applications in the medical engineering, aviation, automotive, and environmental technology fields, as well as other branches of industry, are presented.
An effective process to remove nitrogen-based compounds from fossil fuels without harming the process of sulfur removal is an actual gap in refineries. A success combination of desulfurization and denitrogenation processes capable of completely removing the most environmental contaminates in diesel under sustainable conditions was achieved in this work, applying polyoxometalates as catalysts, hydrogen peroxide as oxidant, and an immiscible ionic liquid as an extraction solvent. The developed process based in simultaneous oxidative desulfurization (ODS) and oxidative denitrogenation (ODN) involved initial extraction of sulfur and nitrogen compounds followed by catalytic oxidation. Keggin-type polyoxomolybdates revealed much higher reusing capacity than the related polyoxotungstate. Effectively, the first catalysts practically allowed complete sulfur and nitrogen removal only in 1 h of reaction and for ten consecutive cycles, maintaining the original catalyst and ionic liquid samples.
This study aimed to extend the application of plasma electrolytic oxidation (PEO) process to the production of immobilized composite photocatalysts with sensitizing nanoparticles (NPs) on the metallic substrate. For this purpose, the immobilized Fe2O3/TiO2 layers with different amounts of sonochemically synthesized Fe2O3 NPs were prepared on the titanium substrate using the PEO method and their structural, morphological, optical, and photocatalytic properties were investigated. The results showed that the immobilized Fe2O3/TiO2 layers with pancake-like morphology were homogeneously formed and the Fe2O3 NPs were uniformly embedded. The participation of the Fe2O3 NPs in layer formation events resulted in the phase transformation of anatase to rutile and an increase in the number of small surface pores. With the increment in the amount of incorporated Fe2O3 NPs, the absorption band-edge of immobilized layers shifted to the longer wavelengths and their light utilization from the visible region of the solar radiation spectrum considerably increased. As a result of these changes, the degradation efficiency of methylene blue aqueous solution under ultraviolet irradiation significantly enhanced with adding 3 g.L⁻¹ Fe2O3 NPs to the phosphate-based electrolyte.
Graphical abstract
Polyoxometalates (POMs) are a large group of anionic polynuclear metal-oxo clusters with discrete and chemically modifiable structures. In most aqueous POM solutions, numerous, and often highly negatively charged, species of different nuclearities are formed. It is rather difficult to determine the dominant POM species or their combination, which is responsible for the specific POM activity, during a particular application. Thus, the identification of all individual speciation profiles is essential for the successful implementation of POMs in solution applications. This review article summarizes species that are present in isopoly- and heteropolyvanadates, -niobates, -molybdates and -tungstates aqueous solutions and covers their stability and transformations. The ion-distribution diagrams over a wide pH range are presented in a comprehensive manner. These diagrams are intended for the targeted use of POMs, and in a clear form shows species that are in equilibrium at the given pH value. Thus, the data accumulated in this review can serve as both a starting point and a complete reference material for determining the composition of POM solutions. Some examples are highlighted where the POM speciation studies led to a detailed understanding of their role in applications. In doing so, we aim to motivate the POM community for more speciation studies and to make the subject more comprehensible, both for synthetic POM chemists and for scientists with different backgrounds interested in applying POMs in biological, medical, electrochemical, supramolecular and nanochemistry fields, or as homogeneous catalysts and other water-soluble materials.
Plasma electrolytic oxidation (PEO), also called micro-arc oxidation (MAO), is an innovative method in producing oxide-ceramic coatings on metals, such as aluminum, titanium, magnesium, zirconium, etc. The process is characterized by discharges, which develop in a strong electric field, in a system consisting of the substrate, the oxide layer, a gas envelope, and the electrolyte. The electric breakdown in this system establishes a plasma state, in which, under anodic polarization, the substrate material is locally converted to a compound consisting of the substrate material itself (including alloying elements) and oxygen in addition to the electrolyte components. The review presents the process kinetics according to the existing models of the discharge phenomena, as well as the influence of the process parameters on the process, and thus, on the resulting coating properties, e.g., morphology and composition.
One‐stage size‐selective method of laser electrodispersion (LED) was used to produce nanostructured NiPd, NiMo and NiW coatings on the surface of alumina, HOPG and Sibunit for the catalytic application. The deposition of nanoparticles produced by LED of bimetallic targets from alloyed or pressed metal powders provides the uniform distribution of both metals on the outer support surface; the metal ratio is similar to that in the original target. The catalytic behaviour of produced “core‐shell” catalysts in comparison with monometallic analogues was tested in two model reactions: the CO oxidation with oxygen on NiPd catalysts supported on alumina and Sibunit; and thiophene oxidation with hydrogen peroxide on NiMo and NiW alumina supported catalysts. Novel LED bimetallic catalysts with extremely low metal content (0.005 %) were superior in terms of activity and stability to monometallic ones and the catalysts obtained by “wet” chemistry methods. Improved catalytic properties of bimetallic LED catalysts are related to the high density of single nanoparticles and the formation of active metal‐oxide interfaces on the support surface.
An adsorbent catalyst was proposed to reduce the leaching of active species of the catalyst and enhance the kinetics of the oxidative desulfurization (ODS) reaction of dibenzothiophene (DBT) from model diesel fuel. By loading phosphotungstic acid (HPW) species onto a zirconium‐modified hexagonal mesoporous silica (Zr‐HMS), a novel catalyst was synthesized and utilized for the ODS process. An ultrafast ODS kinetics was specifically identified using 20%HPW/Zr‐HMS as catalyst. Within 30 min, more than 95% of the 350 ppm DBT content of the model fuel was oxidized by H2O2. The synthesized catalyst retained its sulfur removal ability even after five subsequent ODS reactions and the leaching of HPW species was found to be suppressed successfully. Overall, this new reusable catalyst provided an alternative for highly efficient ultra‐deep desulfurization process.
To achieve a better performance of engineering components, modern design approaches consider the replacement of steel with lightweight metals, such as aluminum alloys. However, bare aluminum cannot satisfy requirements for surface properties in situations where continuous friction is needed. Among the various surface modification techniques, plasma electrolytic oxidation (PEO) is considered as promising for structural applications, owing to its hard and well-adhered ceramic coatings. In this work, the surfaces of two Al alloys (2024 and 6061) have been modified by PEO coating (~180 µm) reinforced with basalt minerals, in order to increase the coefficient of friction and wear resistance. A slurry electrolyte, including a silicate-alkaline solution with addition of basalt mineral powder (<5 µm) has been used. The coating composition, surface morphology, and microstructure were studied using X-ray diffraction, scanning electron, and optical microscopy. Linear reciprocating wear tests were employed for the evaluation of the friction and wear behavior. It was found that the coatings reinforced with basalt mineral showed that the wear and friction coefficients reached values 10 −6-10 −7 (mm 3 N −1 m −1) and 0.7-0.85, correspondingly (sliding distance of 100 m). In comparison with the characteristics of resin-based materials (10 −5-10 −4 (mm 3 N −1 m −1) and 0.3-0.5, respectively), the employment of thin inorganic frictional composites may bring considerable improvement in the thermal stability, durability, and compactness, as well as a reduction in the weight of the final product. These coatings are considered an alternative to the reinforced resin composite materials on steel used in frictional components, for example, clutch disks and braking pads. It is expected that the smaller thickness of the active frictional material (180 µm) reduces the volume of the wear products, extending the service intervals associated with filter and lubricant maintenance.
In order to effectively catalyze the oxidation of dibenzothiophene (DBT) in diesel, a phosphotungstic-based ionic liquid (IL) supported catalyst [C16mim]3PW12O40/TiO2 was prepared through a one-step method. Commercially available TiO2 (C-TiO2), a type of transition metal oxide, was selected as a carrier for comparison. The structure and composition of the catalysts were studied through TG, FT-IR, UV-DRS, wide-angle XRD, N2 adsorption–desorption, SEM and XPS analysis. It was found that the Keggin structure of [C16mim]3PW12O40 was still preserved in the supported catalysts. In addition, the catalysts were applied in extractive coupled catalytic oxidative desulfurization (ECODS) system with H2O2 participating, and dibenzothiophene (DBT) could be totally removed after 1 h under optimum conditions. In addition, factors that affected the desulfurization efficiencies were also been studied in detail. The oxidation product after the reaction was detected by means of GC–MS analysis, DBTO2 (m/z = 216.0) was proved to be the only product of DBT and the possible mechanism was proposed. Moreover, the reusability of the supported ionic liquid catalyst was also investigated, and the oxidation of DBT could still reach 97.8% after eight cycles.
In this study, ordered meso-macroporous titania–silica–polyoxometalate (HPW/SiO2–TiO2) material was prepared in one-pot by evaporation-induced self-assembly (EISA) method, with non-ionic surfactant (P123) and monodisperse polystyrene microspheres applied as co-structure-directing agents. And the oxidative desulfurization (ODS) application of as-synthesized hierarchical nanocomposite materials was tested in model fuel. The characterization results of catalyst suggested that Keggin-type polyoxometalate was successfully incorporated into the ordered meso-macroporous SiO2–TiO2 framework. Moreover, the effect of Lewis acid center of the HPW/SiO2–TiO2 catalyst on ODS process was investigated. The optimum proportion of titanium and silicon ratio on catalyst was found to be 1:1, which exhibited remarkable catalytic performance on aromatic sulfur compounds at mild conditions. It revealed that Lewis acid sites played an important role in selectively adsorb DBT and its derivatives. What’s More, the combination of Lewis acid sites and ordered meso/macroporous architecture of catalyst will further facilitated the mass transport in ODS process. No decrease in the activity was observed after six runs, indicating a good stability of as-prepared catalyst.
Supported ionic liquid (IL) catalysts [Cnmim]3PMo12O40/Am TiO2 (amorphous TiO2) were synthesized through a one-step method for extraction coupled catalytic oxidative desulfurization (ECODS) system. Characterizations such as FTIR, DRS, wide-angle XRD, N2 adsorption–desorption and XPS were applied to analyze the morphology and Keggin structure of the catalysts. In ECODS with hydrogen peroxide as the oxidant, it was found that ILs with longer alkyl chains in the cationic moiety had a better effect on the removal of dibenzothiophene. The desulfurization could reach 100% under optimal conditions, and GC–MS analysis was employed to detect the oxidized product after the reaction. Factors affecting the desulfurization efficiencies were discussed, and a possible mechanism was proposed. In addition, cyclic experiments were also conducted to investigate the recyclability of the supported catalyst. The catalytic activity of [C16mim]3PMo12O40/Am TiO2 only dropped from 100% to 92.9% after ten cycles, demonstrating the good recycling performance of the catalyst and its potential industrial application.
The review describes recent progress on understanding and quantification of the various phenomena that take place during plasma electrolytic oxidation, which is in increasing industrial use for production of protective coatings and other surface treatment purposes. A general overview of the process and some information about usage of these coatings are provided in the first part of the review. The focus is then on the dielectric breakdown that repeatedly occurs over the surface of the work-piece. These discharges are central to the process, since it is largely via the associated plasmas that oxidation of the substrate takes place and the coating is created. The details are complex, since the discharge characteristics are affected by a number of processing variables. The inter-relationships between electrical conditions, electrolyte composition, coating microstructure and rates of growth, which are linked via the characteristics of the discharges, have become clearer over recent years and these improvements in understanding are summarised here. There is considerable scope for more effective process control, with specific objectives in terms of coating performance and energy efficiency, and an attempt is made to identify key points that are likely to assist this.
Hollow nanomaterials are considered to be excellent carriers due to the nanoreactor confinement effect, which can improve the performance of the supported catalysts. In this work, a hollow silica confined defective molybdenum oxide catalyst (MoOx/HS) was obtained by using phosphomolybdic acid grafted polystyrenes as the templates. Compared with solid silica-supported catalyst (MoO3/SS), MoOx/HS could make better use of active components to achieve complete desulfurization. The calculated turnover value (TON) of MoOx/HS was 1.37 mol/mol, which is three times more than that of MoO3/SS. The presence of oxygen defects also facilitated the oxidation reaction. In addition, the catalyst MoOx/HS had good stability and selectivity, and the desulfurization rate of dibenzothiophene (DBT) remained 95.3% after being recycled for 5 times.
The encapsulation of the polyoxomolybdate, H3(PMo12O40).nH2O (PMo12) in the nanoporous MOF-808 framework was carried-out for the first time by a straightforward in-situ method based on a “bottle-around-the ship” approach, to...
Sulfur and nitrogen removal of fossil fuel derivatives has been one of the basic challenges in the industries. For addressing this challenge, catalytic oxidative desulfurization (CATODS) and catalytic oxidative denitrogenation (CATODN) are utilized as practical procedures. Hence, expanding of novel and reasonable oxidation is considered as an important objective for environmental scientists. Therefore, in the present research, TB@PCuMo11@CuO hybrid catalyst was successfully synthesized by reaction of quaternary ammonium salt of mono-copper (II)-substituted phosphomolybdate [(n-C4H9)4N][PCuMo11O39] (TB@PCuMo11) and copper oxide (CuO) through sol–gel method to be utilized in oxidation of dibenzothiophene (DBT), thiophene (TH), carbazole (CBZ), and pyridine (PY). Structure of catalyst, different oxidation systems, various amounts of catalyst, O/S and O/N molar ratio, and reaction temperature and time in both catalytic oxidative desulfurization and catalytic oxidative denitrogenation were investigated. The obtained data were analyzed separately through sum of ranking differences (SRD) chemometrics technique to discriminate the desulfurization and denitrogenation behavior of the catalyst under different conditions. Superb performance of the catalyst for oxidation process was verified based on the agreement between experimental data and computational results. The results suggest that nitrogen-containing structures (NCs) were greatly removed than sulfur-containing structures (SCs). High efficiency of TB@PCuMo11@CuO in the presence of hydrogen peroxide as oxidizing agent can be an encouraging green method with a high capacity for purification of the model fuels under moderate reaction conditions.Graphic abstract
The XW/rGO compounds (XW=Co or Ni modified WO3) have has been utilized as catalysts in the oxidative desulfurization (ODS) process of a liquid model fuel containing dibenzothiophene (DBT). Various characterization methods were carried out to complete evaluations of the prepared catalysts. Moreover, using the GC-MS method, it became clear that the final product of the process was dibenzothiophene sulfone (DBTO2). Furthermore, results showed that under the optimized conditions (oxidant to substrate molar ratio = 6, 75□C and catalyst to substrate molar ratio = 0.08), the DBT content of a model fuel was declined by 100% only within a reaction duration time of 45 min using the CoW (20)/rGO catalyst. Also, the results obtained from the DFT study revealed that, for an efficient reaction over the surface of the catalyst, along with the S…O chalcogen interaction, the strength of the H-bonds interactions (H…O) between the DBT and active sites on catalysts may have tuned-up the driving force of the reaction. Ultimately, the results indicated that the charge transfer at the XW/rGO interface may be tuned by selecting impurity used alongside the WO3 species.
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 H 2 O 2 :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.
In this study, Manganese oxide nanoparticles (MnO2 NPs) are deposited over Zr-based UiO-66 molecular organic framework (MOF) resulting in MnO2/UiO-66 composite which is oxidized with NaClO for the catalytic oxidative desulfurization and denitrogenation of fuel oil. The as-synthesized composites were characterized via FE-SEM, EDX, BET, XPS and FT-IR techniques which confirmed the uniform deposition of MnO2 NPs and resulted in increased surface area and average mesoporous volume of pristine UiO-66. Catalytic results showed that MnO2/UiO-66 oxidized 2000 ppm of DBT (347 ppm Sulfur) and pyridine (502.8 ppm Nitrogen) in 3 min at O/S and O/N of 4, 0.06 g/15 mL catalyst dose and 25 oC. The mechanism behind the super-fast and highly efficacious performance of MnO2/UiO-66 is the ideal synergy among Mn⁴⁺, Zr⁴⁺ and NaClO species, which produced strong oxidizing •OH and •O²⁻ radicals. Under the optimized reaction parameters, much higher removal of DBT and pyridine (100%) was achieved as compared to those of BT, 4,6-DMDBT, indole, and carbazole up to 6th cycles. This study provided important oxidant-catalyst system i.e. MnO2/UiO-66-NaClO for the highly efficacious, super-fast, and time and cost-effective alternative to the large scale oxidative desulfurization and denitrogenation of fuel oils.
A new, high-efficiency catalyzed oxidative desulfurization system is developed. In this system, sulfonated polystyrene spheres (SPS), which are prepared through sulfonating polystyrene resin spheres (PS) at 30 °C, ionic liquids and H2O2 are employed as catalyst, extractant and oxidant, respectively. SPS are characterized with different methods and results show that SPS have hierarchical porous structure, high specific surface area (580 m²/g) and acid content (524 mmol/g). SPS show excellent catalytic property with ionic liquids and 99.8% dibenzothiophene (DBT) in model oil can be removed at 60 °C in 1 h and O/S = 5. Besides, the possible reaction mechanism and process are inferred based on various characterizations and experiments. Peroxy species (-SO2OOH) is the important oxidant intermediate, which oxidates DBT to corresponding sulfone. Moreover, the catalyst could be reused for 6 times without evident decrease of desulfurization efficiency .
In recent years, considerable research has long been devoted to the development of metallic materials with excellent surface properties through various surface modification techniques. A plasma electrolytic oxidation (PEO), one of the electrochemical coatings, has considered the eco-friendly wet coating in alkaline-based electrolytes where the surface characteristics of metal would be altered significantly by electrochemical reactions assisted by plasma discharges, resulting in the formation of hard, conformal, adhesive inorganic layer on the metal substrate. This review described a couple of the scientific principles including transient discharge behavior at breakdown, nucleation and growth of inorganic layer, and electrophoresis for incorporating inorganic particle. It outlined the essential microstructural features, which were related to defect structure, plasma-induced microstructural transformation, phase transition, and roles of inorganic agents. The protective nature of the present coating was highlighted by considering structural reliabilities, such as tribological and corrosion performances. In addition, the emerging applications arising from functional properties of the present coating, such as biomedical, catalysis, light, and energy performances, were reviewed. The benign approaches used to improve the structural and functional properties of coating layers are described utilizing pre- and post-treatments of PEO.
The iron-chromium-aluminum alloy (FeCrAl) is an exceptional support for highly exothermic and endothermic reactions that operate above 700 °C in chemically aggressive environments, where low heat and mass transfer rates limit reaction yield. FeCrAl two- and three-dimensional structured networks-monoliths, foams, and fibers-maximize mass transfer rates, while their remarkable thermal conductivity minimizes hot spots and thermal gradients. Another advantage of the open FeCrAl structure is the low pressure drop due to the high void fraction and regularity of the internal path. The surface Al2O3 layer, formed after an initial thermal oxidation, supports a wide range of metal and metal oxide active phases. The aluminum oxide that adheres to the metal surface protects it from corrosive atmospheres and carbon (carburization), thus allowing FeCrAl to operate at a higher temperature. The top applications are industrial burners, in which compact knitted metal fibers distribute heat over large surface areas, and automotive tail gas converters. Future applications include producing H2 and syngas from remote natural gas in modular units. This Review summarizes the specific preparation techniques, details process operating conditions and catalyst performance of several classes of reactions, and highlights positive and challenging aspects of FeCrAl.
In this work, polyoxometalates-based monomer ionic liquid, dimer ionic liquid and polyionic liquid were designed and prepared. Then supported catalysts were synthesized by loading polyoxometalate derivatives on the surface of graphene oxide (GO). The catalysts before and after loading were characterized via many tests such as scanning electron microscope (SEM), infrared spectroscopy (IR), X-ray powder diffraction (XRD) and so on. The influences of ionic liquid type and carrier on desulfurization activity were carried out. The result shows that supported catalyst-based polyionic liquid (P[Vim]POM/GO) performed high activity and excellent recyclability in extraction-oxidation desulfurization (EODS) due to unique state of polyoxometalate and the support of graphene oxide. In addition, the possible mechanism of oxidation dibenzothiophene (DBT) with H2O2 was proposed according to the kinetic study and gas chromatography-mass spectrometer (GC-MS) result.
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 [email protected]@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.
High efficiency was found for desulfurization and denitrogenation processes to treat diesel using either the hybrid material {[MoO3(2,2′‐bipy)][MoO3(H2O)]}n or the octanuclear complex [Mo8O22(OH)4(di‐t Bu‐bipy)4] (2,2′‐bipy = 2,2′‐bipyridine, di‐t Bu‐bipy = 4,4′‐di‐tert ‐butyl‐2,2′‐bipyridine)) as catalysts. These processes were employed in a single procedure to simultaneously remove the sulfur (dibenzothiophene, 4‐methyldibenzothiophene and 4,6‐dimethyldibenzothiophene) and nitrogen (indole and quinoline) compounds from diesel. A reaction time of 2 h was sufficient to achieve at least 99.9% S removal and 97% N removal. Furthermore, the catalytic systems presented a high capacity to be reused/recycled for consecutive desulfurization/denitrogenation cycles.
In this study, platinum (Pt) supported on titanium (Ti) mesh catalysts for catalytic hydrogen combustion were prepared by depositing Pt as a thin-layer on metallic or calcined Ti mesh. The Pt thin-layer could be stabilized as uniformly distributed, near nano-sized particles on the surface of calcined Ti mesh by exposing the freshly sputtered Pt to hydrogen. Temperatures between 478 and 525 °C were reached during hydrogen combustion and could be maintained at a hydrogen flow rate of 0.4 normal liter (Nl)/min for several hrs. It was determined that Ti mesh calcination at ≥900 °C formed an oxide layer on the surface of Ti wires, which prevented significant Pt aggregation. X-ray photoelectron spectroscopy revealed that the surface of Ti mesh was fully converted to TiO2 at ≥900 °C. Raman spectroscopy showed that the majority of TiO2 was present in the rutile phase, with some minor contribution from anatase-TiO2. The calcined Ti support was stable through all investigations and did not indicate any signs of degradation.
Plasma electrolytic oxidation (PEO) is a complex process, accompanied by spark discharge and intensive gas evolution around metal anode. In this paper, the gas released from Zirlo alloy electrode during PEO process in KF solution and phosphate solution was collected and its composition was analyzed by gas chromatograph (GC). The possibility of H2 evolution from Zirlo alloy anode was evaluated and its formation mechanism was discussed. It was found that the gas released from discharging anode contained H2 and O2. The H2 up to 81.6 vol% was detected under strong plasma discharge in phosphate solution. Furthermore, a little CO was also detected while the glycerol was added into electrolyte. Hence, a large amount of H2 could be evolved on Zirlo alloy anode during PEO process, which was different from the traditional electrochemical theory and common knowledge of PEO technology for O2 evolution on anode. Relatively less H2 was released in KF solution due to weak plasma discharge. The H2 concentration evolved during PEO process was related to the intensity of plasma discharge. It was believed that the H2 and O2 mainly resulted from the direct thermal decomposition of water vapour in plasma discharge zone, though the electrolyte was also decomposed to form H2, O2 and CO.
Titanium-supported oxide layers of W, W + Zn and W + Mn, formed by plasma electrolytic oxidation, were established to catalyze the peroxide oxidation of thiophene. The most active compositions based on Zn-W-containing PEO layers were also tested in the oxidation of a number of organosulfur compounds and diesel fuel desulfurization. Preliminary covering the samples by zwitterionic liquid (ZIL) made it possible to achieve residual sulfur content as low as 6 ppm. The change in the morphology and composition of samples with and without ZIL was studied during catalytic tests. It was found that ZIL reduces the etching of the sample surfaces when interacting with the reaction medium.
Hierarchically structured ionic liquid-based Mo/TiO2 materials with three-dimensional ordered macroporous (3DOM) and short-ranged ordered mesoporous structure are synthesized by two steps self-assembling process and applied as catalysts in oxidative desulfurization (ODS) process. TG-DSC, SEM, TEM, XRD, BET, XPS, and FT-IR measurements demonstrate that as-fabricated catalysts possess ordered meso/macroporous structure with Mo species dispersed homogeneously on TiO2 matrix. In addition, the influences of sol-gelation temperatures and amount of nonionic surfactant on the mesoscopical order of catalyst are also discussed in detail. It can be demonstrated that catalyst prepared at mild sol-gel temperature (40 °C) and proper nonionic surfactant usage (3.0 g) exhibits the highest catalytic activity for aromatic sulfides. In the ODS reaction, 500 ppm of dibenzothiophene (DBT) in the model fuel can be completely removed within 100 min at 30 °C due to the well-designed ordered secondary mesopores and interconnected macroporous structure of catalyst, which provides rapid diffusion channels of reactant molecules to the inner surface and improves the exposure of Mo species on the mesoporous wall. Furthermore, as-synthesized catalyst can be reused for 15 runs without significant decrease in catalytic activity.
Calcium phosphate (Ca-P) coatings were fabricated by micro-arc oxidation (MAO) on AZ31B magnesium alloy in near-neutral pH solutions (pH 7.6–7.9) and the influences of EDTA-CaNa2, phytic acid (IP6), phosphoric acid (PA), and treatment time on coating properties were investigated by an orthogonal experiment. The results show that coating corrosion resistance is synergistically determined by coating characteristics with coating thickness playing a particularly important role. EDTA-CaNa2 acts as a corrosive agent of magnesium alloys and the increased concentration increases calcium content but decreases corrosion resistance of MAO coatings. As a strong chelating agent, IP6 can promote EDTA-CaNa2 solubility and therefore increases the calcium content more effectively than PA does. Compared with PA, IP6 more effectively improves corrosion resistance mainly by increasing coating thickness and bonding strength between coating and substrate, although the uniformity of anodic coatings becomes worse due to the greater interfacial tension of the IP6 solution than that of the PA solution. During MAO, P and F compete with each other to enter into anodic coatings. F amount in MAO coatings is closely related to the coating biocompatibility. MAO coatings developed in the solution composed of both IP6 and PA achieve low F content (3.49 at%) and good biocompatibility, while those fabricated in solutions containing only IP6 or PA achieve high F content (higher than 19.00 at%) and exhibit high toxicity.
Harvesting clean energy from the fuel feedstocks is of paramount significance in the field of environmental science. In this dynamic area, the desulfurization provides a valuable contribution by eliminating the sulfur compounds from the fuel feedstocks to ensure the utilization of fuels without the emission of toxic sulfur oxides (SOx gases). Nonetheless, the inadequacy of the current industrial technique (hydrodesulfurization, HDS) in the removal of refractory sulfur (RS) compounds and the stringent rules imposed on fuel sulfur level have kindled the research on other desulfurization methods like oxidative desulfurization (ODS). With the capacity of eliminating RS compounds under mild conditions, ODS is endorsed as a suitable replacement or complementary to HDS. ODS, in common, consists of two steps such as i) oxidation and ii) extraction. The oxidation of sulfur compounds is carried out using a suitable catalyst (hereafter, termed as ODS catalyst) in the presence of an oxidant. Choosing a suitable ODS catalyst for the industrial applications is still a quest among the various types of catalysts reported so far. With this outline, herein, all the types of ODS catalysts along with their synthetic methods, reactivity and mechanistic insights are reviewed. The activity of ODS catalysts could be influenced by the factors like the type of RS compounds, solvents, fuels, etc and those factors are reviewed. The effects of ionic liquids, light, and ultrasound on the performance of ODS catalysts are also briefly summarized. The opportunities and challenges for the ODS catalysts are comprehensively explicated in the end. Through this review, the systematic information about the types of ODS catalysts including basic definition, preparative methods, reactivity and mechanism can be comprehended. Furthermore, this review discloses the merits and demerits related to highlighting the catalytic ODS as a replacement or complementary to HDS.
Desulfurization of fuel has been an important issue in fuel refining process. Hydrodesulfurization, as a traditional and commercial desulfurization technique for removing sulfur compounds, has been widely researched for decades. But as the environmental policy implemented on fuel becoming stricter, it is more difficult to remove organic sulfur compounds by hydrodesulfurization technology. Therefore, non-hydrodesulfurization technologies developed rapidly in recent years. Among all novel desulfurization technologies, oxidative desulfurization (ODS) functions best with its mild reaction condition and efficient desulfurization capacity. Heteropolyacid (HPA) has been intensively investigated because the HPA has discrete ionic structure and high proton mobility, which makes it extremely promising in catalysis. As a result, HPA has been applied in a variety of synthetically selective transformations of organic substances and the ODS is one of them. However, HPA have shortcomings such as their high solubility in polar solvents and low specific surface area. To overcome these problems, many works have been done to combine heteropolyacids with other materials. The main derivatives of HPA used in ODS are supported heteropolyacid, phase transfer heteropolyacid catalyst and polyoxometalate based ionic liquid. The catalytic activity and reusability of HPA are substantially increased after modification. The works on heteropolyaicds for ODS from 2010 to 2019 will be summarized in this review.
Ni modified MoO3 (Ni-MoO3) had been synthesized by a facile one-step hydrothermal technique and was used for oxidative desulfurization (ODS) of dibenzothiophene (DBT) in the decalin/acetonitrile biphasic system with H2O2 as oxidant, the effect of different operating conditions was investigated. Under the optimal reaction condition, Ni-MoO3 catalyst showed excellent ODS performance toward DBT, the highest sulfur removal efficiency can be up to 99.8% and sulfur content was wiped out from 5000 to 10 ppm, which is more effective than the recent reported MoO3-based catalysts. The reaction kinetics obeyed the pseudo-first-order equation with an apparent rate constant of 0.076 min⁻¹, which is twice that of pure MoO3 (0.035 min⁻¹). The ODS mechanism of DBT with Ni-MoO3 was explored by combining radical scavenger, FT-IR experiments and theoretical analysis, proving that surface oxygen vacancies and Lewis acid sites play important roles in the high-efficiency ODS reaction with Ni-MoO3 catalyst.
A serial of ordered meso-macroporous phosphotungstic acid (HPW) supported on SiO2 nanocomposites were successfully prepared by a homogeneous precipitation method, using monodispersed polystyrene (PS) microspheres and cationic surfactant as structure directing agent. These nanocomposites were used as catalysts for oxidative desulfurization (ODS) of model fuel. The materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption isothrem, X-ray diffraction (XRD), and Fourier transform infrared spectra (FTIR). The characterization results suggested that the as-prepared material possessed ordered meso-macroporous architectures with Keggin type phosphotungstic acid dispersed homogeneously in SiO2 matrix. Under the selected reaction conditions, dibenzothiophene (DBT) in model fuel can be removed within 2 h at room temperature (30 °C). In addition, only 1.2% of efficiency lose than the fresh catalyst even after 5 cycles.
A comprehensive study of the magnetic behavior, morphology, and composition of Fe-containing oxide coatings on aluminum and titanium has been carried out to investigate the origin of their ferromagnetism. The coatings have been formed by the plasma electrolytic oxidation (PEO) technique in slurry electrolytes containing colloidal particles of iron(III) hydroxides. On the surface of coatings on Al, iron is distributed unevenly concentrating in defective areas with a large number of small pores, and near large pores. On the surface of coatings on Ti, iron and titanium are distributed in antiphase in areas of comparable size. Within the pores, iron concentration appears about 5–10 times higher and oxygen concentration 3–4 times lower than their average concentration over the surface. In both cases, localization of the areas with ferromagnetic properties follows the peculiarities of iron distribution on the surface. The magnetic fraction in the coatings on aluminum appears to be represented by iron-aluminum spinel Fe3-xAlxO4 with x > 0.06, likely cation-deficient. Elemental iron and traces of iron hydroxides are also possibly present. In the coatings on titanium, titanomagnetite (Fe3-xTixO4, where x ∼ 0.2–0.3) or its oxidized analogue, titanomaghemite, appear to be present, and possibly also some Fe–Ti alloy particles.
Removal of sulfur- and nitrogen-containing compounds (SCCs and NCCs) from commercial fuel is very important since those impurities can cause various problems including catalyst deactivation and acid rain. Because of the limitations of the conventional refinery methods, development of a new method such as oxidative desulfurization (ODS) is highly desirable. Metal-organic frameworks (MOFs)-based and MOF-derived nanohybrid materials were suggested as a good catalyst for ODS of fuels. Moreover, removal of NCCs via oxidation with MOF-derived catalyst was also reported even though the technique is just emerging. Therefore, it is required to analyze the reported results; and more importantly to suggest a new research direction; and finally, to estimate the possibility of new desulfurization/denitrogenation technology that might replace/compensate studied technologies. This review might be quite beneficial not only to accumulate or understand the reported results but also to develop new efficient catalysts for the probable commercialization of the ODS/ODN technology.
Highly efficient, deep desulfurization of a multi-component model diesel containing benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) has been achieved by using the peroxophosphomolybdate [(n-C4H9)4N]3{PO4[MoO(O2)2]4} (Q3PMo4) directly as catalyst, and aqueous H2O2 as oxidant. Q3PMo4 behaves as a heterogeneous catalyst in the complete oxidation of the various sulfur compounds to the corresponding sulfones within 3 h at 70 °C, using a relatively low H2O2/S molar ratio of 3.7, and could be recycled for ten times with only a minimal decrease in activity. A study was performed to adapt the catalyst Q3PMo4 for the removal of sulfur from a real untreated diesel while maintaining a low, economically desirable, H2O2/S molar ratio of 3.7. The highest desulfurization performance was achieved in the presence of an extraction solvent during the catalytic oxidative stage, reinforced by two extraction steps before and after sulfur oxidation. Under these conditions, the sulfur content of the real diesel was reduced from 2300 to 500 ppm (78% desulfurization efficiency) after 3 h.
In this manuscript novel heterogeneous catalysts for fuel desulfurization via peroxide oxidation are reported. The obtained catalysts combine high catalytic activity and stability with perfect synthetic availability, their composition and structure were ascertained. The catalysts represent supported ionic liquid phases (SILPs): Brønsted acidic ILs, namely 4-(3′- ethylimidazolium)-butanesulfonate, with two heteropolyacids (HPA) (sulfated ionic liquid protonated by H3PMo12O40 or H3PW12O40). Silica and γ-Al2O3 were used as support materials. These compositions ensure higher stability of heteropolyanions and make the catalyst stable over several successive oxidation cycles. The most active catalyst based on phosphomolybdic acid provides a high conversion rate for thiophene, thioanisole, and dibenzothiophene (turn over frequency of about 150–1200 h⁻¹ per mole of HPA). Another important benefit of the reported systems is the desulfurization of diesel fuel with a very high efficiency (residual amount of sulfur <10 ppm) under mild conditions.
Detailed characterization of W species and amorphous material in plasma electrolytic oxidation (PEO) coatings formed in W-containing electrolyte is important to PEO study. In this paper, PEO coatings were prepared on an Al-Cu-Li alloy in a mixed electrolyte of silicate and tungstate, and the coatings were characterized by a series of advanced analysis methods. Scanning electron microscopy (SEM) shows that PEO leads to a bi-layered coating with big internal pores and the W element was enriched close to the coating/substrate interface. X-ray photoelectron spectroscopy (XPS) shows that hexavalent tungsten is the predominant species; however, weak peaks for free-state W have been found in the inner coating exposed by grinding. Focused ion beam (FIB) was used to prepare an electron-transparent sample across the coating/substrate interface for the transmission electron microscopy (TEM) characterization. TEM results show that free-state W exists in the form of nanocrystalline particles, while the amorphous material was found surrounding the large internal pores of the coating. The amorphous material consists of O, Al, W, Si and Cu, and the elements other than O have comparable atomic percentages. According to models proposed in this paper, the nanocrystalline W particles were formed by the thermite reaction between fine molten Al drops and tungsten oxides. However, amorphous material was formed due to its complex composition and the rapid cooling rate brought from the ingress of electrolyte into the big pores.
A combination of catalytic oxidation and extraction was used for the desulfurization of a model diesel containing benzothiophene, dibenzothiophene and 4,6-dimethyldibenzothiophene, or a real diesel sample with a sulfur content of 2300 ppm. The catalysts used were the soluble peroxo compound (nBu4N)3{PO4[WO(O2)2]4} (PW4) and a supported material denoted as PW4@TMA-SBA-15 that was prepared by immobilization of PW4 in an ordered mesoporous silica (SBA-15) derivatized with propyltrimethylammonium groups (TMA). The supported catalyst was characterized by FT-IR, FT-Raman, ³¹P and ¹³C MAS NMR spectroscopies, powder X-ray diffraction and scanning electron microscopy. Under optimized conditions (H2O2/S molar ratio = 7, 70 °C, acetonitrile as extraction solvent), both catalysts led to complete desulfurization of the model diesel within a reaction time of 2 h. The desulfurization systems could be recycled 10 times with only a slight decrease in performance being observed between the 9th and 10th oxidative desulfurization cycles. Application of the PW4 system to the real diesel led to an outstanding desulfurization efficiency of 89% after a reaction time of 2 h.
A number of researches have been concerned about the development of β-type titanium alloys because they can present good biocompatibility, non-cytotoxicity, suitable mechanical and corrosion resistance behavior. However, due to their chemical inertness property, the surfaces of the novel Ti alloys must be modified by different methods to improve their bioactivity. This work is focused on the electrochemical surface modification of Ti-10Nb and Ti-20Nb alloys by Plasma Electrolytic Oxidation (PEO) method in 1.0 M H3PO4 electrolyte at 250 V. X-Ray diffraction showed that both binary Ti-Nb alloys are mainly composed of (α+β) phase. The PEO treatment led to producing rough and thick titanium and niobium oxides films on the Ti-Nb alloys. The oxide films produced on the Ti-10Nb alloys have the anatase structure, whereas those formed on the Ti-20Nb alloy have an amorphous structure observed by Raman Spectroscopy. Hardness and elastic modulus were measured by instrumented indentation. Both oxide films are harder than their substrates (4.0–6.0 GPa) and have reduced elastic modulus values (100–110 GPa) compared to cp-Ti (reference). Linear reciprocating tests were employed to study the surface wear resistance of the samples. Among the non-treated samples, the Ti-10Nb alloy presented a better wear performance. In addition, the titanium and niobium oxides films formed on the Ti-10Nb alloy presented the most resistant surfaces. In relation to the cellular viability evaluation, the oxide films produced on both Ti-Nb alloys did not show any sign of cytotoxicity. Indeed, the porosity, roughness and chemical composition of the resulting titanium and niobium oxides films were able to promote osteoblast cells attachment and proliferation on their surfaces. Based on these findings, the PEO electrochemical treatment on Ti-10Nb alloy can form porous oxides coating and could be used as a reference line for manufacturing more wear resistant and non-cytotoxic surfaces to biomedical applications.
The aim of this article is to study the extractive-catalytic oxidative desulfurization (ECODS) of the model oil containing several model S-containing compounds as well as N-containing compound using a heterogeneous vanadium substituted Dawson-type polyoxometalate catalyst under atmospheric pressure and temperature lower than 100 °C. The catalyst was prepared by ion exchange with alkyl ammonium derivatives covalently anchored to silica gel. The potential of this methodology was illustrated by oxidation of 100% quinoline and 80% of total sulfur in model oil containing 500 ppmw sulfur and 70% of total sulfur in model oil 1500 ppmw in less than 30 min of reaction, in the absence of solvent. However, when acetonitrile was employed as an extractive solvent, the desulfurization was increased considerably. Under the reaction conditions, activated catalyst and acetonitrile, solvent to oil ratio 1:6, could remove approximately 100% of quinoline, 95% of sulfur from 500-ppmw model oil, 87% of sulfur from 1500-ppmw model oil in less than 30 min. The catalyst is very active in ECODS and can be reused fifth times from 500-ppmw model oil and third times from 1500-ppmw model oil without an important decrease in activity. The ECODS could remove 83% of total sulfur from 1235-ppmw-S real diesel.
This paper described the synthesis of meso/macroporous phosphotungstic acid (HPW) /TiO2 catalyst with quaternary ammonium bromide and monodispersed polystyrene spheres (PS) as dual-template. The synthetic parameters, such as concentration of the templates and the alky chain length of quaternary ammonium bromide was studied carefully and optimized to generate catalyst with regulated porous features. The chemical properties of the catalyst was also investigated, X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) measurements confirmed the Keggin-type HPW were highly dispersed on the TiO2 framework. The optimal meso/macroporous HPW/TiO2 catalyst exhibited excellent catalytic activity in the oxidation of refractory sulphur compounds such as benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT). DBT was removed within 2 h at 30 °C under selected reaction conditions and the apparent activation energy for DBT oxidation was calculated to be 45.7 kJ/mol. The high ODS reaction rate of catalyst could be attributed to the combination of unique meso/macroporous architecture allowing for efficient mass transport of reactants and products in pore channel and its high surface area, large mesoporous size, and pore volume enabling sufficient exposure of catalytic active sites. Moreover, the meso/macroporous HPW/TiO2 catalyst also exhibited excellent reusability with no obviously degradation even after eight cycles.
High levels of sulfur organic compounds (SOCs) and nitrogen organic compounds (NOCs), which are contaminants present in diesel fuel and straight run gas oil (SRGO), were removed using tungsten/zirconia catalysts and hydrogen peroxide by oxidative desulfurization and oxidative denitrogenation reactions. Two tungsten sources were used: tungstic acid and ammonium metatungstate. The catalysts obtained by anionic exchange at low pH with tungstic acid showed remarkable homogeneity and high W dispersion attributed to tetrahedral W species and full dibenzothiophene (DBT) oxidation was achieved in 5 min of reaction. On the other hand, the catalysts obtained by impregnation with ammonium metatungstate developed mainly octahedral species with less DBT oxidation. It was also found that tetrahedral species generate more acidity than octahedral species. A density functional theory computational study confirmed the observed DBT oxidation trend shown by tetrahedral and octahedral W species on the peroxide-activated catalysts. Diesel fuel and SRGO were desulfurized and denitrogenated to a high extent: 97% in diesel fuel and 70% in SRGO for sulfur compounds and 96% in diesel fuel and 89% in SRGO for nitrogen compounds, whereas C1–C3 dibenzothiophenes, 4-methyl dibenzothiophene, and 4,6-dimethyl dibenzothiophene were fully removed. The elimination of SOCs and NOCs present in fuels can be effectively carried out in a single process to obtain clean fuels.
Nowadays, a continuously worldwide concern for development of process to produce ultra-low sulfur and nitrogen fuels have been emerged. Typical hydrodesulfurization and hydrodenitrogenation technology deals with important difficulties such as high pressure and temperature operating condition, failure to treat some recalcitrant compounds and limitations to meet the stringent environmental regulations. In contrary an advanced oxidation process that is ultrasound assisted oxidative desulfurization and denitrogenation satisfies latest environmental regulations in much milder conditions with more efficiency. The present work deals with a comprehensive review on findings and development in the ultrasound assisted oxidative desulfurization and denitrogenation (UAOD) during the last decades. The role of individual parameters namely temperature, residence time, ultrasound power and frequency, pH, initial concentration and types of sulfur and nitrogen compounds on the efficiency are described. What's more another treatment properties that is role of phase transfer agent (PTA) and solvents of extraction step, reaction kinetics, mechanism of the ultrasound, fuel properties and recovery in UAOD are reviewed. Finally, the required future works to mature this technology are suggested.