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An unprecedented and straightforward strategy towards the activation of metal-organic frameworks UiO-66(Zr) and UiO-66(Hf) in oxidative desulfurization reactions was developed. Post-synthetic treatment of poor-defect pristine UiO-66 materials with chloride-based salts (for example TiCl4) leaded to the preparation of more active and recyclable heterogeneous catalysts for oxidative desulfurization processes. The pristine UiO-66(Hf) showed to be an inactive catalyst; however, after activation treatment 80% of total desulfurization was achieved after 1 h. Also, UiO-66 (Zr) increased appreciably its activity after treatment with chloride-based salts (from 62% to 97% for the sample treated with TiCl4). The insertion of chloride in UiO-66 framework did not retain the counter-cation Ti(IV). The possible interaction of chloride with UiO-66 framework enhances catalytic activity without structural degradation of catalyst, even after consecutive reaction cycles. Chloride activation method opened a new route to activate efficiently catalytic UiO-66 MOFs. This is a cost-effective method capable to be feasible to other MOFs structures, promoting their catalytic capacities and enlarging their catalytic application.

This work presents an effective and fast procedure to valorize the main waste produced from the biodiesel industry, i.e., the glycerol. The acetalization of glycerol with acetone represents an effective strategy to produce the valuable solketal, a fuel additive component. In this work, the catalytic efficiency of different commercial heteropolyacids (HPAas) was compared under a solvent-free system. The HPAs used were H3[PW12O40] (PW12), H3[PMo12O40] (PMo12) and H4[SiW12O40] (SiW12). The influence of reactional parameters such as reactants stoichiometry, catalyst concentration and reaction temperature were investigated in order to optimize experimental conditions to increase cost-efficiency and sustainability. HPAs demonstrated to be highly efficient for this type of reaction, presenting a high and fast glycerol conversion, with high selectivity to solketal under sustainable conditions (solvent-free system and room temperature medium). The activity of HPAs using 3% to glycerol weight and a glycerol/acetone ratio of 1:15 followed the order: PW12 (99.2%) > PMo12 (91.4%) > SiW12 (90.7%) as a result of the strong acidic sites after 5 min. In fact, only 5 min of reaction were needed to achieve 97% of solketal product in the presence of the PW12 as a catalyst. This last system presents an effective, selective and sustainable catalytic system to valorize glycerol.

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.

Oxidative desulfurization (ODS) is a method of removing sulfur from diesel fuel that has the potential to complement or even replace conventional hydrodesulfurization processes in oil refineries. One of the most promising variants of ODS is extractive and catalytic ODS (ECODS) in which the organic sulfur compounds in the liquid fuel are oxidized and extracted in situ from the oil phase into an extractant phase. In this study, the desulfurizalion of model and real diesel fuel has been performed in ECODS systems employing two different types of deep eutectic solvents (DESs), prepared by combining polyethylene glycol (PEG) as hydrogen bond donor with tetrabutylammonium chloride (TBACl) or choline chloride (ChCl) as hydrogen bond acceptor. The ECODS systems were evaluated with the complexes [MoO2Cl2(DMB)(2)] (1) and [MoO2Cl2(DEO)] (2) (DMB - N,N-dimethylbenzamide, DEO = N,N'-diethyloxamide) as catalysts and 30 wt% H2O2 as oxidant. The effects of different reaction conditions, such as the amount of catalyst, H2O2 and DES, and reaction temperature, were investigated. The combination of complex 1 with the DES ChCl/PEG showed the best performance for the removal of dibenzothiophene, 4-methyldibenzothiophene and 4,6-di methyldibenzothiophene from a high-sulfur (3000 ppm) model diesel, allowing a desulfurization efficiency of 99.6% to be attained at 70 degrees C within 2 h. By applying the optimized model diesel ECODS systems to the treatment of a commercial untreated diesel with a sulfur content of 2300 ppm. 82% of sulfur compounds could be eliminated. These promising results indicate that DESs are a viable alternative to ionic liquids as extraction solvents in ECODS processes. (C) 2020 Elsevier B.V. All rights reserved. project REQUIMTE-LAQV [FCT (Fundacao para a Ciencia e a Tecnologia)] [UID/QUI/50006/2019] project CICECO-Aveiro Institute of Materials - Foundation for Science and Technology/MCTES [UIDB/50011/2020, UIDP/50011/2020] FCTPortuguese Foundation for Science and TechnologyEuropean Commission [SFRH/BD/102783/2014] European UnionEuropean Commission [SFRH/BD/102783/2014] MCTES European Social Fund through the program POPH of QREN info:eu-repo/semantics/publishedVersion

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.

Polyoxometalates have been demonstrated to be efficient catalysts for the activation of oxidants in desulfurization processes. Successful results on desulfurization using polyoxometalates and hydrogen peroxide to desulfurize model oils and liquid fuels were reported and can be found in the literature. The desulfurization is an actual subject with notable interest for refineries and fuel cost, and consequently, it is important to focus the scientific community to work in desulfurization technology in order to develop catalytic systems based on polyoxometalates capable to be reused, stable, efficient, and selective. Therefore, the main goal is the design of heterogeneous polyoxometalate based catalysts. This chapter pretends to inform the research society about the scientific directions that have been taken using heterogeneous polyoxometalate catalysts in oxidative desulfurization of simulated and real liquid fuels. In addition, future perspectives are proposed to cover the actual needs of this area.

A novel composite has been prepared through the immobilization of the Keggin sandwich-type [Sm(PMo11O39)2]11− anion (SmPOM) on large-pore silica spheres previously functionalized with trimethylammonium groups (TMA). The resulting SmPOM@TMA-LPMS material has been evaluated as heterogeneous catalyst in a biphasic desulfurization 1:1 diesel/extraction solvent system using H2O2 as oxidant. Preliminary experiments were conducted with different extraction solvents, acetonitrile and [BMIM]PF6 ionic liquid. The optimized extractive and catalytic oxidative desulfurization system (ECODS) with [BMIM]PF6 was able to reach complete sulfur removal from a model diesel containing 2100 ppm S in just 60 min (10 min of initial extraction + 50 min of catalytic step). The reutilization of catalyst and extraction phase has been successfully performed without loss of desulfurization efficiency in consecutive cycles, turning the process more sustainable and cost-effective. The remarkable results with simulated diesel have motivated the application of the catalyst in the desulfurization of untreated real diesel and 74% of efficiency was achieved after only 2 h for three consecutive cycles.

Efficient and recyclable liquid–liquid extraction and catalytic oxidative desulfurization (ECODS) systems for the removal of refractory sulfur compounds from liquid fuels are reported that use the cyclopentadienyl molybdenum tricarbonyl complexes [CpMo(CO)3Me] (1), [CpMo(CO)3(CH2-pC6H4-CO2Me] (2) and [CpMo(CO)3CH2COOH] (3) as catalyst precursors. An ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, was used as both extractant and reaction medium, entrapping the active homogeneous MoVI catalysts that are formed in situ under the operating catalytic conditions (aqueous H2O2 as oxidant, 50 °C). The high sulfoxidation activity of the catalyst formed from 1 was largely responsible for enabling >99% desulfurization within 1 h of a model oil containing 1-benzothiophene, dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene (2000 ppm S). The IL/catalyst phase could be repeatedly recycled with no loss of desulfurization efficiency. By sequentially performing extractive desulfurization and ECODS steps, 83–84% sulfur removal was achieved for untreated real diesel and jet fuel samples with initial sulfur contents of ca. 2300 and 1100 ppm, respectively.

This work presents a successful recycling system based in homogeneous polyoxometalate catalysts to desulfurize model and real diesels. Various Keggin-type polyoxometates entrapped in a room temperature ionic liquid (RTIL) phase were investigated. The desulfurization process here proposed conciliates efficiently an extraction and an oxidative catalytic process under sustainable and moderate conditions (H2O2 as oxidant, 50 °C). The ionic liquid acts as an extraction solvent and also as an effective immobilization medium for the active homogeneous catalysts. The zinc-polyoxometalates presented high stability and high capacity to be recycled for various consecutive cycles with no loss of desulfurization efficiency. Complete desulfurization of model diesel was achieved at short reaction time (3 h). Under the same experimental conditions, 80% of sulfur was removed from real diesel (Sinitial = 2300 ppm).

The present research investigation brings out a novel and relevant catalytic application for the family of MIL-101 metal–organic framework (MOF) materials. The porous Fe(III) terephthalate MOF, MIL-101(Fe) and the corresponding amino-functionalized material, NH2-MIL-101(Fe) showed to be highly active and 100% selective heterogeneous catalysts in the ring opening of cyclohexene oxide in the presence of aniline. The activity of both MOF materials was similar, mainly after 24 h, achieving yields of 87% for trans-2-(phenylamino)-cyclohexanol. The stability and robustness of these MOF materials were confirmed and their capacity to be recycled was also demonstrated. Furthermore, cyclic voltammetry studies revealed that the amine-functionalization of the MIL-101(Fe) results in a significant improvement of the electrochemical response over the unfunctionalized compound, constituting an exceptional advantage of the NH2-MIL-101(Fe) as a future potential electrocatalyst.

An emerging strategy to improve the performance of porous metal–organic framework (MOF) materials as heterogeneous catalysts is reported. The incorporation of the iron-substituted polyoxometalate (POM) TBA4[PW11Fe(H2O)O39] (PW11Fe) in porous MOF NH2-MIL-101(Fe), leading to a novel composite based MOF material, PW11Fe@NH2-MIL-101(Fe), was revealed to be a significant approach to increase the efficiency of the MOF material as a regioselective catalyst for the ring opening of styrene oxide with aniline. The conversion after 1 h of reaction using NH2-MIL-101(Fe) is 22% and increases to 100% when PW11Fe@NH2-MIL-101(Fe) is employed as catalyst. It is noteworthy that the catalytic performance of this composite material is also considerably better than that obtained with the respective physical mixture under similar conditions. Furthermore, PW11Fe@NH2-MIL-101(Fe) revealed to be a remarkable selective heterogeneous catalyst for the studied reaction (100% selectivity to the 2-phenylamino-2-phenylethanol isomer) with significant robustness and recyclability.

The complexes [MoO2Cl2(DMB)(2)] (1) and [MoO2Cl2(DEO)] (2) (DMB = N,N-dimethylbenzamide, DEO = N,N'-diethyloxamide) have been evaluated as catalysts in extractive-catalytic oxidative desulfurization (ECOD) of a simulated diesel fuel. Using the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) as extraction solvent and H2O2 as oxidant, ultra-deep desulfurization (S-content from 3000 ppm to < 10 ppm) was possible within a reaction time of 1-3 h, and the systems Catalyst/[BMIM]PF6 could be recycled for five times without significant decrease in activity. The S-content of a real untreated diesel was lowered by 94.4% from 2300 ppm to 129 ppm after only 2 h of reaction using the ECOD process with 2 as catalyst. REQUIMTE-LAQV [FCT (Fundacao para a Ciencia e a Tecnologia)] [UID/QUI/50006/2019] CICECO - Aveiro Institute of Materials (FCT) [UID/CTM/50011/2019] Centre of Marine Sciences - CCMAR [UID/Multi/04326/2019] FCT/MCTESPortuguese Foundation for Science and Technology FCTPortuguese Foundation for Science and Technology [SFRH/BD/102783/2014] European UnionEuropean Union (EU) [SFRH/BD/102783/2014] MCTES European Social Fund through the program POPH of QREN FCT, I.P.

The creation of more sustainable and high efficient desulfurization system, capable to operate under cost-effective conditions, led to the application of peroxopolyoxometalates as active oxidative catalysts. These compounds present active peroxo groups in their structure that promote easily the oxidation of sulfur compounds in the presence of low amounts of oxidant (H2O2/S = 4). The sustainability of the desulfurization of a multicomponent model diesel (2000 ppm S) was increased by the optimization of various parameters, such as nature and volume of extraction solvent, oxidant and catalyst. The Venturello peroxotungstate ((Bu4N)3PW4) showed to be a catalyst able to complete desulfurize a model diesel (after only 40 min), under lower amounts of solvent, oxidant and catalyst, than the analogues peroxomolybdate ((Bu4N)3PMo4) compound. Furthermore, the (Bu4N)3PW4/[BMIM]PF6 system was able to be reused for six consecutive desulfurization cycles maintaining its efficiency. The oxidized sulfur compounds were removed from [BMIM]PF6 phase in the end of each catalytic cycle. This simple procedure guarantees the cost-efficiency of the process, promoting the reuse of the catalyst and the solvent for various consecutive cycles, without the need of heterogenization techniques.

The zinc-substituted polyoxotungstate [PW11Zn(H2O)O-39](5-) (PW11Zn) has been encapsulated within the aluminium(III) 2-aminoterephthalate NH2-MIL-101(Al) metal-organic framework (MOF) either directly through a one-pot microwave-assisted synthesis or by an impregnation method. The resultant composite materials were characterized by elemental analysis, powder X-ray diffraction, FTIR spectroscopy, and P-31 magic-angle spinning (MAS) NMR spectroscopy. The desulfurization of a model diesel containing three refractory organosulfur compounds (1-benzothiophene, dibenzothiophene, and 4,6-dimethyldibenzothiophene) was studied with the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate as an extractant, the PW11Zn@MOF composites as sulfoxidation catalysts, and aqueous H2O2 as an oxidant. The composite obtained by direct synthesis was the most efficient catalyst and led to almost complete desulfurization of the model diesel under mild conditions. Moreover, the solid catalyst could be recovered readily and recycled without significant loss of desulfurization performance. The application of this system to the treatment of a real diesel sample provided a very good sulfur removal of 83% when combined with liquid-liquid extraction.

A composite material comprising the chromium terephthalate metal-organic framework MIL-101 and the tetrabutylammonium (TBA) salt of a zinc-substituted polyoxotungstate anion, TBA(4.2)H(0.8)[PW11Zn(H2O)O-39] ( denoted PW11Zn), has been prepared by an impregnation method and characterized by powder X-ray diffraction, scanning electron microscopy, N-2 adsorption/desorption, thermogravimetric analysis, FT-IR, FT-Raman and P-31 magic-angle spinning (MAS) NMR spectroscopies. The characterization data reveal that the polyoxometalate was homogeneously encapsulated within the cages of the support without affecting its crystalline structure and morphology. Both the homogeneous catalyst PW11Zn and the composite material PW11Zn@MIL-101 exhibit high activity in the extractive and catalytic oxidative desulfurization of a model oil containing dibenzothiophene, 1-benzothiophene and 4,6-dimethyldibenzothiophene. Complete desulfurization of the model oil could be achieved within 2 h by using the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate as extraction solvent, aqueous 30% H2O2 as oxidant and a reaction temperature of 50 degrees C. When acetonitrile was used as extraction solvent instead of the IL, the heterogeneous catalyst PW11Zn@MIL-101 could be easily recovered and reused several times without leaching or loss of activity. (C) 2014 Elsevier B.V. All rights

The first catalytic active composites based on CoAl2O4 nanoparticles with different size (5.5 and 2.5 nm) were successfully prepared using a simple methodology of incorporation into MIL-101(Cr) framework, CoAl-x@MIL(Cr). Characterization of CoAl-x@MIL(Cr) composites by elemental analysis, vibrational spectroscopy (FT-IR and FT-Raman), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) confirmed the successful preparation and stability of the support structure after nanoparticle immobilization. A remarkable catalytic performance was found for thioanisole oxidation under sustainable conditions (95% of conversion after 30 min of reaction) and the catalytic application of the most active composite was extended to styrene oxidation. Higher catalytic performance was achieved for the composite prepared with larger CoAl2O4 nanoparticles. The recyclability and the stability of composites after catalytic use were investigated. For the CoAl-x@MIL(Cr) catalytic systems, the loading parameter instead of the nanoparticle size seemed to have a pronounced influence in the heterogeneous catalytic performance. The confinement effect promoted by MIL-101(Cr) cavities associated to the higher number of catalytic active centers (CoAl2O4) is clearly more important than the size of the catalytic nanoparticles used.

In the last decade, polyoxometalates have been demonstrated to be efficient catalysts for the activation of oxidants in desulfurization processes. Successful results on desulfurization using polyoxometalates and hydrogen peroxide to desulfurize model oils and liquid fuels were reported and can be found in the literature. The desulfurization is an actual subject with notable interest for refineries and fuel cost, and consequently it is important to focus the scientific community to work in desulfurization technology in order to develop catalytic systems based on polyoxometalates capable to be reused, stable, efficient and selective. Therefore, the main goal is the design of heterogeneous polyoxometalate based catalysts. This chapter pretends to inform the research society about the scientific directions that have been taken using heterogeneous polyoxometalate catalysts in oxidative desulfurization of simulated and real liquid fuels. In addition, future perspectives are proposed to cover the actual needs of this area.

An aluminum 2-aminoterephthalate based metal-organic framework (MOF) material was applied for the first time to prepare highly efficient heterogeneous catalysts in desulfurization processes. Sandwich-type [Eu(PW11O39)(2)](11-) polyoxometalate (POM) was supported on Al(III) and Cr(III) MIL-type MOFs, NH2-MIL-53(Al) and MIL-101(Cr), and extensive characterization confirmed the incorporation of the POM on the two supports. The catalytic performance of the two composite materials, POM/MIL(Al) and POM/MIL(Cr), was evaluated in the oxidative desulfurization (ODS) of a model fuel containing some of the most common refractory sulfur compounds in diesel. Both composite materials have shown to be active and robust heterogeneous catalysts for the efficient removal of the sulfur-containing compounds from the model diesel, and the influence of the solid support on the catalytic performance of the active species was further assessed. The POM/MIL(Al) revealed notable catalytic performance, since complete desulfurization was obtained after 2 h of reaction. Furthermore, this remarkable heterogeneous catalyst revealed to be stable and recyclable for various catalytic cycles.

The desulfurization efficiency of various hybrid zinc-substituted polyoxometalates ([PW11Zn(H2O)O39]5−, abbreviated as PW11Zn) was here investigated for the first time and optimized using sustainable systems conciliating successfully the liquid–liquid extraction and the oxidative catalytic process. Initially, the desulfurization studies were performed using a model diesel containing a mixture of the most refractory sulfur compounds and later extended to an untreated real diesel. In both cases, acetonitrile was used as extraction solvent and aqueous H2O2 as oxidant. High level of desulfurization was achieved using model and untreated diesels after few hours. The quaternary ammonium catalysts (TBAPW11Zn and ODAPW11Zn) showed higher catalytic desulfurization efficiency than the ionic liquid catalyst (BMIPW11Zn). The TBAPW11Zn behaved as a homogeneous catalyst immobilized in the extraction solvent, while the ODAPW11Zn with the long carbon chain behaved as a heterogeneous catalyst capable to be recovered from the system. Both quaternary ammonium catalysts showed to be successfully reused/recycled for various consecutive desulfurization cycles.

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Hybrid multilayer films composed of poly(ethylenimine) and sandwich-type silicotungstates, K13[Ln(SiW11O39)2] (Ln(SiW11)2), Ln3+ = Eu, Tb, Dy, were prepared on glassy carbon electrodes, quartz and glass slides using the electrostatic LbL self-assembly method. The film build up, monitored by electronic spectroscopy, showed a regular stepwise growth indicating a strong interaction between layers. The X-ray photoelectron spectroscopy measurements corroborated the successful fabrication of the hybrid films with the PEI–POMs composition and pointed out that the intrinsic charge compensation from the film components is the major contribution, although there is some extrinsic charge compensation from the counter cations from the POMs and electrolyte. All the LbL films showed W-based reduction processes due to the immobilized POMs; voltammetric responses revealed a kinetic facilitation of the first reduction process in the immobilized Tb(SiW11)2 and Dy(SiW11)2 polyanions relatively to the free POMs and scan rate effect showed that the tungsten reduction process for all POMs is surface-confined. The photoluminescence properties of PEI/Eu(SiW11)2 multilayer films were investigated and showed the characteristic Eu3+ emission pattern.

This work proposes an efficient desulfurization system to produce low sulfur diesel under sustainable and moderate experimental conditions. Treatment of a real diesel with a sulfur content of 2300 ppm led to 80% desulfurization after 2 h. The processes used conciliate liquid-liquid extraction and sulfur oxidative catalysis. The catalytic performance of the commercial Keggin-polyoxomolybdate H3[PMo12O40] (PMo12) was strategically increased by simple cation exchange, using a long carbon chain (ODAPMo12, ODA = CH3(CH2)17(CH3)3N), and by its incorporation into the Metal-Organic Framework (MOF) NH2-MIL-101(Cr), forming a new active heterogeneous PMo12@MOF composite catalyst. Activity of both catalysts was similar, however, the solid catalyst could be easily recovered and reused, and its stability was confirmed after multiple continuous cycles.

Sandwich-type of luminescent silicotungstates were prepared using the inorganic ligand [SiW11O39](8-)(SiW11) coordinating different lanthanide ions (Eu3+, Tb3+, Dy3+): Eu(SiW11)(2), Tb(SiW11)(2) and Dy(SiW11)(2). The potassium salts of these compounds were characterised by several techniques and the crystal structure of Eu(SiW11)(2) was studied. The lanthanide ion in the sandwich structure reveled to have some influence in the electrochemical behaviour of these compounds in aqueous solutions, mainly in the first of the two reduction processes observed for the tungsten atoms. The influence of scan rate on the voltammetric characteristics of the first tungsten reduction process led to the conclusion that the process was diffusion-controlled. The pH of the electrolyte solution showed significant effect on the electrochemical behaviour of these compounds, suggesting that the tungsten reductions processes are accompanied by addition of two to three protons. The photoluminescence properties of Eu(SiW11)(2) and Tb(SiW11)(2) were investigated in some detail, namely as a function of temperature and pressure (with exposure to a high vacuum of ca. 5 x 10(-6) mbar). Both compounds are iso-structural with a single Ln(3+) site and with absence of water molecules coordinated to the lanthanide ions. Contrary to Eu(SiW11)(2), the Tb(SiW11)(2) compound is not optically active at room temperature and shows a very sensitive photoluminescence with the temperature on the range of 11-150 K which was interpreted by the effect of a back energy transfer de-excitation process. (C) 2012 Elsevier Ltd. All rights reserved.