Polyoxometalate as effective catalyst for the deep desulfurization of diesel oil

Aiming at the deep desulfurization of the diesel oil, a comparison of the catalytic effects of several Keggin type POMs, including H₃PW_xMo_12?xO₄₀ (x = 1, 3, 6), Cs_2.5H_0.5PW₁₂O₄₀, and H₃PW₁₂O₄₀, was made, using the solution of DBT in normal octane as simulated diesel oil, H₂O₂ as oxidant, and acetonitrile as extractant. H₃PW₆Mo₆O₄₀ was found to be the best catalyst, with a desulfurization efficiency of 99.79% or higher. Hence, it is promising for the deep desulfurization of actual ODS process. The role of the main factors affecting the process including temperature, O/S molar ratio, initial sulfur concentration, and catalyst dosage, was investigated, whereby the favourable operating conditions were recommended as T = 60 °C, O/S = 15, and a catalyst dosage of 6.93 g (H₃PW₆Mo₆O₄₀)/L (simulated diesel). With the aid of GC–MS analysis, sulfone species was confirmed to be the only product after reaction for 150 min. Furthermore, macro-kinetics of the process catalyzed by H₃PW₆Mo₆O₄₀ was studied, from which the reaction orders were found to be 1.02 to DBT and 0.38 to H₂O₂, and the activation energy of the reaction was found to be 43.3 kJ/mol. Moreover, the catalyst recovered demonstrated almost the same activity as the fresh.     

杂多酸盐催化合成柠檬酸三丁酯研究

制备了1-（3-磺酸基）丙基-3-甲基咪唑磷钼酸盐（[MIMPS]₃PMo₁₂O₄₀）、1-（3-磺酸基）丙基-3-甲基咪唑磷钨酸盐（[MIMPS]₃PW₁₂O₄₀）和1-（3-磺酸基）丙基-3-甲基吡啶磷钨酸盐（[PyPS]₃PW₁₂O₄₀）3种杂多酸盐,用于催化柠檬酸和正丁醇合成柠檬酸三丁酯（TBC）,考察了各催化剂的催化效果。其中,[MIMPS]₃PMo₁₂O₄₀具有最好的催化效果,在其催化下,考察了反应条件对酯化率的影响。结果表明：当醇酸物质的量比为4.5:1.0、反应温度为130℃、反应时间为3.5h、催化剂用量为柠檬酸质量的5%时,酯化率可达98.3%,且催化剂具有较好的重复使用性能,重复使用5次后,酯化率依然保持在94%以上。     

A novel [Bmim]PW/HMS catalyst with high catalytic performance for the oxidative desulfurization process

To effectively reduce the sulfur content in model fuel, [Bmim]PW/HMS catalyst was synthesized through impregnating the hexagonal mesoporous silica (HMS) support by phosphotungstic acid (HPW) and ionic liquid [Bmim] HSO₄. Physical structure characterizations of the catalysts showed that HMS retained mesoporous structure, and [Bmim] PW was well dispersed on the support of HMS. The catalytic activity of the [Bmim]PW/HMS was evaluated in the oxidative desulfurization process, and the optimal reaction conditions including loading of the catalysts, reaction temperature, catalyst amount, O/S (H₂O₂/sulfur) molar ratio and agitation speed were investigated. Under the optimal reaction conditions, the conversion of benzothiophene (BT), dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (4, 6-DMDBT) could reach 79%, 98%, 88%, respectively.     

Oxidation desulfurization of fuel using pyridinium-based ionic liquids as phase-transfer catalysts

In this work, several ionic liquids based on pyridinium cations are prepared. The ionic liquids are employed as phase-transfer catalysts (PTCs) for phase-transfer catalytic oxidation of dibenzothiophene (DBT) dissolved in n-octane. The partition coefficients of DBT between ionic liquids and n-octane are investigated. Then H₂O₂-formic acid is used as an oxidant and ionic liquids are used as PTCs. The reaction turns to be heterogeneous and desulfurization rate of DBT increased apparently. When IL ([BPy]HSO₄) is used as PTC, and the condition are: temperature is 60 °C, time is 60 min, H₂O₂/sulfur molar ratio (O/S) is 4, the desulfurization rate reaches the maximum (93.3%), and the desulfurization of the real gasoline is also investigated, 87.7% of sulfur contents are removed under optima reaction conditions. The PTC [BPy]HSO₄ can be recycled for five times without significant decrease in activity.     

Deep oxidative–extractive desulfurization of fuels using benzyl‐based ionic liquid

Four benzyl‐based ionic liquids (ILs) were synthetized and used for deep desulfurization of model oil and real diesel fuel. The removal efficiencies of benzothiophene (BT) and dibenzothiophene (DBT) with [Bzmim][NTf₂] and [Bzmim][SCN] as extractants are higher than that with [Bzmp][NTf₂] and [Bzmp][SCN] as extractants. The desulfurization capability follows the Nernst's Law. A reactive extraction mathematical model for desulfurization was established. An oxidative‐extractive two‐step deep desulfurization method was developed. DBT was first oxidized by H₂O₂ with CH₃COOH as catalyst and then the unoxidized DBT and uncrystallized dibenzothiophene sulfoxide (DBTO₂) in model oil were extracted by [Bzmim][NTf₂], and finally the removal efficiency was 98.4% after one‐stage extraction. Besides, the removal efficiency of 4,6‐DMDBT was 96.4% after oxidation and one‐stage extraction processes. Moreover, the oxidative‐extractive two‐step deep desulfurization method was also effective for desulfurization of diesel fuel. The removal efficiency of sulfur reached up to 96% after oxidation and three‐stage cross‐current extraction processes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4023–4034, 2016     

Preparation,characterization and catalytic performance of HPW-TUD-1 catalyst on oxidative desulfurization

By incorporating H₃PW₁₂O₄₀ (HPW) heteropolyacid into mesoporous TUD-1 materials, a series of HPW-TUD-1 catalysts were synthesized. Nitrogen adsorption–desorption isotherm, XRD and FTIR characterizations showed that these catalyst exhibited mesoporous structure, and HPW presented in the catalysts with Keggin structure. The catalytic performances of the HPW-TUD-1 catalysts were tested through the oxidative desulfurization (ODS) process of dibenzothiophene (DBT) model oil. The results showed that the obtained 20HPW-TUD-1 catalyst displayed excellent catalytic activity and recover ability for ODS. The desulfurization rate of DBT reached up to 98.1%, and almost no catalytic activity loss was observed after three recycles of the catalyst.     

Activity and stability of amino-functionalized SBA-15 immobilized 12-tungstophosphoric acid in the oxidative desulfurization of a diesel fuel model with H2O2

In this study, the stability and the catalytic activity of an ordered mesoporous SBA-15 immobilized 12-tungstophosphoric acid (H₃PW₁₂O₄₀, HPW) in the oxidative desulfurization (ODS) of benzothiophene (BT) and dibenzothiophene (DBT) were improved by a post-synthesis-grafting method. In this method, SBA-15 was functionalized to provide a large number of amine groups for the immobilization of HPW through electrostatic binding with (3-aminopropyl) triethoxysilane (APTES) using triflic acid as a protonated agent. The materials were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), N₂ adsorption–desorption, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The results show that the structure of functionalized SBA-15 support and the active phase of the HPW remained intact after immobilization. The synthesized PW^–H₃N⁺-SBA-15 catalyst showed a high catalytic activity for ODS, achieving BT and DBT conversion of 99.9% and 100% with the reaction conditions of reaction temperature of 50?°C, H₂O₂ dosage of 1?mL, catalyst dosage of 0.03?g, and reaction time 5 and 1?h, respectively. The catalyst also showed a high reusability after up to four cycles, for which the conversion of the fourth reaction was 90.0% for both BT and DBT.     

Oxidative desulfurization of Gas oil by polyoxometalates catalysts

Several polyoxometalates: Na₂HPM₁₂O₄₀, H₃PM₁₂O₄₀, Na₂HPM₁₂O₄₀, (VO)H[PM₁₂O₄₀] and (n-Bu₄N)₃[PM₁₂O₄₀] (M = Mo and W) as well as (n-Bu₄N)_3 + x[PW_12−xV_xO₄₀] (x = 0–3) were synthesized and characterized. Benzothiophene, dibenzothiophene and 4,6-dimethyl-dibenzothiophene were used as model sulfur compounds in gas oil. The oxidation reaction was performed using different polyoxometalates as catalyst and H₂O₂/acetic acid. The experimental results show that the W-based polyoxometalate catalysts are more active than the Mo catalysts. The oxidation reactivity of the catalysts depends on the type of countercation: Na⁺ > H⁺ > (VO)⁺ > (n-Bu₄N)⁺. In a series of (n-Bu₄N)_3 + x [PW_12−xV_xO₄₀] (x = 0–3) the order of catalytic activity is V₃ > V₂ > V₁ > V₀. The reactivity order of the sulfur compounds is: dibenzothiophene > 4,6-dimethyldibenzo-thiophene > benzothiophene. The catalytic system in this work was used for the oxidation of gas oil combined with solvent extraction to remove sulfur content in gas oil. Under mild reaction condition, high sulfur removal up to 98% can be achieved with high oil recovery (90%).     

Fast proton conductor under anhydrous condition synthesized from 12-phosphotungstic acid and ionic liquid

In this study, we synthesized a molecular hybrid conductor electrolyte using PWA ([H₃PW₁₂O₄₀·nH₂O]) and [1-butyl-3-methylimidazole][bis-(fluoromethanesulfonyl) amide] ([BMIM][TFSI]) ionic liquid. The [BMIM][TFSI] ionic liquid can interact with the strongly acidic PWA. The hybrids were hydrophilic, and included some water molecules in the structure of the hybrids. The water molecules remained up to 80 °C, contributing to improve conductivity under an anhydrous N₂ atmosphere. The conductivity of PWA-[BMIM][TFSI] hybrid under anhydrous conditions increased from 10⁻⁴ S/cm to 0.04 S/cm at 60 °C. The conductivity of the hybrids at each temperature was higher than that of pure PWA and [BMIM][TFSI] under anhydrous condition. It can be due to the protonic carriers.     

Deep desulfurization of fuels catalyzed by surfactant-type decatungstates using H2O2 as oxidant

Oxidation of dibenzothiphene (DBT) in model oil with H₂O₂ using surfactant-type decatungstates Q₄W₁₀O₃₂ (Q = (CH₃)₃NC₁₆H₃₃, (CH₃)₃NC₁₄H₂₉, (CH₃)₃NC₁₂H₂₅ and (CH₃)₃NC₁₀H₂₁) as catalysts was studied. The surfactant-type decatungstates were synthesized and characterized. The suitable reaction condition of deep desulfurization was suggested: n(DBT):n(catalyst):n(H₂O₂) = 1:0.01:3, 60 °C for 0.5 h, under which the DBT conversion can reach 99.6% with [(CH₃)₃NC₁₆H₃₃]₄W₁₀O₃₂ as catalyst. The length of carbon chains of quaternary ammonium cations played a vital role in the catalytic activity of surfactant-type decatungstates, that is, the longer the carbon chain of quaternary ammonium cation of a catalyst was, the better the activity of this catalyst showed. [(CH₃)₃NC₁₆H₃₃]₄W₁₀O₃₂ exhibited the best catalytic performance and can be recycled for six times without significant decrease in catalytic activity. Using benzothiphene (BT) and 4,6-dimethyldibenzothiphene (4,6-DMDBT) as substrates in model oil, surfactant-type decatungstates also showed high catalytic activity. During desulfurization process, BT conversion can reach 99.6% at 3.25 h, while 99.4% of 4,6-DMDBT conversion reached at 1.25 h, with the temperature of 60 °C under atmospheric pressure. The sulfone can be separated from the oil using N,N-dimethylformamide (DMF) as an extractant, and the sulfur content can be lowered from 1000 to 4 ppm. For real diesel, the sulfur removal can reach 93.5% after five times extraction.     

Effect of CsxH3?xPW12O40 addition on the catalytic performance of ZnFe2O4 in the oxidative dehydrogenation of n-butene to 1,3-butadiene

Oxidative dehydrogenation of n-butene to 1,3-butadiene over ZnFe₂O₄ catalyst mixed with Cs _x H_3−x PW₁₂O₄₀ heteropolyacid (HPA) was performed in a continuous flow fixed-bed reactor. The effect of Cs _x H_3−x PW₁₂O₄₀ addition on the catalytic performance of ZnFe₂O₄ was investigated. Cs _x H_3−x PW₁₂O₄₀ itself showed very low catalytic performance in the oxidative dehydrogenation of n-butene. However, addition of small amount of Cs _x H_3−x PW₁₂O₄₀ into ZnFe₂O₄ enhanced the catalytic performance of ZnFe₂O₄ catalyst. The catalytic performance of ZnFe₂O₄-Cs _x H_3−x PW₁₂O₄₀ mixed catalysts was closely related to the surface acidity of Cs _x H_3−x PW₁₂O₄₀. Among the catalysts tested, ZnFe₂O₄-Cs_2.5H_0.5 PW₁₂O₄₀ mixed catalyst showed the best catalytic performance. Strong acid strength and large surface acidity of Cs_2.5H_0.5PW₁₂O₄₀ was responsible for high catalytic performance of ZnFe₂O₄-Cs_2.5H_0.5PW₁₂O₄₀ mixed catalyst. Thus, Cs_2.5H_0.5PW₁₂O₄₀ could be utilized as an efficient promoter and diluent in formulating ZnFe₂O₄ catalyst for the oxidative dehydrogenation of n-butene.     

Biodiesel production from soybean oil catalyzed by multifunctionalized Ta2O5/SiO2-[H3PW12O40/R] (R = Me or Ph) hybrid catalyst

Mesoporous Ta₂O₅ materials functionalized with both alkyl group and a Keggin-type heteropoly acid, Ta₂O₅/SiO₂-[H₃PW₁₂O₄₀/R] (R = Me or Ph), was prepared by a single step sol–gel co-condensation method followed by a hydrothermal treatment in the presence of a triblock copolymer surfactant. The catalytic performance of the resulting multifunctionalized organic–inorganic hybrid materials was evaluated by a direct use of soybean oil for biodiesel production in the presence of 20 wt% myristic acid under atmosphere refluxing, and the influences of the catalyst preparation approaches, functional component loadings, and molar ratios of oil to methanol on the catalytic activity of the Ta₂O₅/SiO₂-[H₃PW₁₂O₄₀/R] were studied. In addition, the recyclability of the hybrid materials was evaluated via four catalytic runs. Finally, the network structures of the hybrid materials and the functions of the incorporated alkyl groups on the catalytic activity of the materials were put forward.     

Single-walled carbon nanotubes functionalized with polydiphenylamine as active materials for applications in the supercapacitors field

Composites based on polydiphenylamine (PDPA) doped with heteropolyanions of H₃PW₁₂O₄₀ and single-walled carbon nanotubes (SWNTs) were prepared by electrochemical polymerization of diphenylamine (DPA) on carbon nanotube films deposited onto Pt electrodes. HRTEM studies reveal that the electrochemical polymerization leads to the filling the spaces between tubes which compose the bundles, creating a monolithic film on the Pt electrode. The resulting composites were tested as active materials in supercapacitors. Resonant Raman scattering studies showed that the electropolymerization of DPA in the presence of H₃PW₁₂O₄₀ and SWNTs leads to the covalent functionalization of SWNTs with doped PDPA. The covalent functionalization of SWNTs with PDPA doped with H₃PW₁₂O₄₀ heteropolyanions was revealed by FTIR spectroscopy, based on the changes in the vibrational features of PDPA and H₃PW₁₂O₄₀. These changes included i) a down-shift of the PDPA IR bands, which was attributed to the C–H bending vibrational mode of benzene (B), C_aromatic–N, C–C stretching (B) + C–H bending (B) and C–C stretching vibrations of the B ring, from 1174, 1321, 1495 and 1603 cm^− 1 to 1165, 1313, 1487 and 1599 cm^− 1, respectively; ii) a change in the peak positions of IR bands associated with the W = O and P-O-W vibration modes of H₃PW₁₂O₄₀; and iii) a down-shift of the IR band situated in the spectral range 650–725 cm^− 1, which was assigned to the inter-ring deformation vibration mode.The characterization of symmetric solid-state supercapacitors was performed for electrodes prepared from i) SWNTs functionalized with PDPA doped with H₃PW₁₂O₄₀ heteropolyanions, ii) SWNTs electrochemically decorated with H₃PW₁₂O₄₀ heteropolyanions, and iii) PDPA doped with H₃PW₁₂O₄₀ heteropolyanions. Preliminary results indicate high discharge capacitance values of up to 157.2 mF/cm² for SWNTs functionalized with PDPA doped with H₃PW₁₂O₄₀ heteropolyanions. The discharge capacitance of this material is superior to those recorded for SWNTs electrochemically decorated with H₃PW₁₂O₄₀ heteropolyanions (~ 18.2 mF/cm²) and PDPA doped with H₃PW₁₂O₄₀ heteropolyanions (~ 62.1 mF/cm²).     

Regeneration of H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> catalyst in the direct preparation of dichloropropanol (DCP) from glycerol and hydrochloric acid gas

Methods for regenerating H₃PW₁₂O₄₀ catalyst in the solvent-free direct preparation of dichloropropanol (DCP) from glycerol and hydrochloric acid gas were investigated. Regenerated H₃PW₁₂O₄₀ catalyst was then applied to the solvent-free direct preparation of DCP. In the solvent-free direct preparation of DCP, selectivity for DCP over H₃PW₁₂O₄₀ catalyst regenerated by method I (recovery of solid H₃PW₁₂O₄₀ catalyst by evaporating homogeneous liquidphase product solution) significantly decreased with increasing recycling run, while that over H₃PW₁₂O₄₀ catalyst regenerated by method II (regeneration of H₃PW₁₂O₄₀ catalyst by oxidative calcination of solid product recovered by method I) was slightly decreased with no significant catalyst deactivation with respect to recycling run. On the other hand, selectivity for DCP over H₃PW₁₂O₄₀ catalyst regenerated by method III (regeneration of H₃PW₁₂O₄₀ catalyst by recrystallization and subsequent oxidative calcination of solid product recovered by method II) was the same as that over fresh catalyst without any catalyst deactivation with respect to recycling run. Thus, method III was found to be the most efficient method for the regeneration of H₃PW₁₂O₄₀ catalyst.     

Enhancement of oxygen reduction by incorporation of heteropolytungstate into the electrocatalytic ink of carbon supported platinum nanoparticles

Nafion stabilized inks of Vulcan XC-72 supported platinum (20 wt.%) nanoparticles (Pt/XC-72) were utilized to produce electrocatalytic films on glassy carbon. The catalysts were modified (activated) with phosphododecatungstic acid H₃PW₁₂O₄₀ (PW₁₂). Comparison was made to bare (PW₁₂-free) electrocatalytic films. Electroreduction of dioxygen was studied at 25 °C in 0.5 mol dm⁻³ H₂SO₄ electrolyte using rotating disk voltammetry. For the same loading of platinum (≈95 μg cm⁻²) and for the approximately identical distribution of the catalyst, the reduction of oxygen at a glassy carbon electrode modified with the ink containing PW₁₂ proceeded at ca. 30-60 mV more positive potential (depending on the PW₁₂ content), and the system was characterized by a higher kinetic parameter (rate of heterogeneous electron transfer), when compared to the PW₁₂-free electrocatalyst. Gas diffusion electrodes with Pt/XC-72 supported on carbon paper (Pt loading 1 mg cm⁻²) were also tested. Under the same experimental conditions, while the exchange current density and the total resistance contribution to polarization components, computed from the galvanostatic polarization curves were found to be clearly higher and lower, respectively, for the ink modified with PW₁₂ relative to the unmodified system. The results demonstrate that addition of heteropolytungstatic acid (together with Nafion) enhances the electrocatalytic activity of platinum towards reduction of oxygen.     

Fabrication of micellar heteropolyacid catalysts for clean production of monosaccharides from polysaccharides

A micellar heteropolyacids (HPAs) catalyst had been prepared using surfactant cetyltrimethyl ammonium bromide (CTAB) and H₃PW₁₂O₄₀ as precursors. These micellar [C₁₆H₃₃N(CH₃)₃]_xH_3 − xPW₁₂O₄₀ had been characterized to be micellar structure and the catalytic activity was evaluated by the hydrolysis of polysaccharides to the reducing sugars. The best catalytic activity was obtained over [C₁₆H₃₃N(CH₃)₃]H₂PW₁₂O₄₀ (abbreviated as (C₁₆TA)H₂PW), which showed 100% conversion and 99.6% selectivity within 60 min at 80 °C for hydrolysis of sucrose. And it was also active for the conversion of starch and cellulose. The leaching test showed that the HPA micellar catalysts have an excellent stability and can be used as heterogeneous catalysts for six times.     

Synthesis of Keggin-type lacunary 11-tungstophosphates encapsulated into mesoporous silica pillared in clay interlayer galleries and their catalytic performance in oxidative desulfurization

Keggin-type lacunary polyoxotungstates [PW₁₁O₃₉(H₂O)]^7 − (PW₁₁) and metal-modified [PW₁₁O₃₉(H₂O)M]^5 − (M = Ni^2 + or Co^2 +) were incorporated into the mesoporous silica pillared clays (MSPC) by a hydrothermal sol–gel method. The resulting materials retain the layered structure of the clay precursor and possess a mesoporous structure. The catalytic performance of the materials was tested using oxidative desulfurization of dibenzothiophene-containing model oil as a probe reaction. The results indicated that PW₁₁-MSPC possess an excellent catalytic performance.     

Oxidative Desulfurization of Model Diesel Using a Fenton‐Like Catalyst in the Ionic Liquid [Dmim]BF4

A Fenton‐like catalyst prepared from tetrabutylammonium chloride and ferric trichloride was characterized by Fourier transform infrared, UV‐vis and Raman spectroscopy. The catalyst (C₄H₉)₄NFeCl₄ (TBAFeCl₄) in an extraction and catalytic oxidative desulfurization (ECODS) system containing H₂O₂ and the ionic liquid (IL) 1‐decyl‐3‐methylimidazolium tetrafluoroborate ([Dmim]BF₄) exhibited high catalytic activity for the removal of dibenzothiophene (DBT) in model diesel. Desulfurization with the Fenton‐like catalyst TBAFeCl₄ in ECODS involves the structural distortion of DBT via polarization of the IL and its subsequent oxidation. The catalytic system could be recycled multiple times without significant decrease in desulfurization activity due to the high stability of the system.     

On the active site in H3PW12O40/SiO2 catalysts for fine chemical synthesis

The surface environment and structural evolution of silica supported phosphotungstic acid (H₃PW₁₂O₄₀) catalysts have been investigated as a function of acid loading. H₃PW₁₂O₄₀ clusters are deposited intact upon the silica surface, adopting a Stranksi-Krastanov growth mode forming a two-dimensional adlayer which saturates at 45wt% acid. Intimate contact with the silica support perturbs the local chemical environment of three tungstate centres, which become inequivalent with those in the remaining cluster, suggesting an adsorption mode involving three terminal W==O groups. Above the monolayer, H₃PW₁₂O₄₀ clusters form three-dimensional crystallites with physico-chemical properties indistinguishable from those in the bulk heteropoly acid. These H₃PW₁₂O₄₀/SiO₂ materials are efficient for the solventless isomerisation of α-pinene under mild reaction conditions. Activity scales directly with the number of accessible perturbed tungstate sites at the silica interface; these are the active species.     

Preparation and photocatalytic activity of Keggin-ion tungstate and TiO2 hybrid layer-by-layer film composites

Keggin ions (PW₁₂O₄₀³⁻ (PW₁₂), SiW₁₂O₄₀⁴⁻ (SiW₁₂), H₂W₁₂O₄₀⁶⁻ (H₂W₁₂)) and TiO₂ hybrid thin films were prepared using the layer-by-layer method. Their photocatalytic activities were investigated using gaseous 2-propanol decomposition. All films were transparent in the visible wavelength range. For 2-propanol decomposition, H₂W₁₂ was the most effective for the combination with TiO₂ despite having the smallest TiO₂ deposition amount. The photocatalytic activity of the PW₁₂–TiO₂ hybrid film was increased 2.3 times by visible light with UV illumination. This increase was less remarkable for hybrid films of other Keggin ions, suggesting that the visible light excitation of reduced PW₁₂ plays an important role in the enhancement of 2-propanol decomposition.