Two quaternary ammonium catalysts based on the monovacant polyoxotungstate (PW
O
, abbreviated as PW
) were prepared and characterized. The desulfurization performances of the PW
-based hybrids (of ...tetrabutylammonium and trimethyloctadecylammonium, abbreviated as TBAPW
and ODAPW
, respectively), the corresponding potassium salt (K
PW
O
, abbreviated as KPW
) and the peroxo-compound (TBA-PO
WO(O
)
, abbreviated as TBAPW
) were compared as catalysts for the oxidative desulfurization of a multicomponent model diesel (2000 ppm S). The oxidative desulfurization studies (ODS) were performed using solvent-free systems and aqueous H
O
as oxidant. The nature of the cation in the PW
catalyst showed to have an important influence on the catalytic performance. In fact, the PW
-hybrid catalysts showed higher catalytic efficiency than the peroxo-compound TBAPW
, known as Venturello compound. TBAPW
revealed a remarkable desulfurization performance with 96.5% of sulfur compounds removed in the first 130 min. The reusability and stability of the catalyst were also investigated for ten consecutive ODS cycles without loss of activity. A treated clean diesel could be recovered without sulfur compounds by performing a final liquid/liquid extraction diesel/EtOH:H
O mixture (1:1) after the catalytic oxidative step.
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The adsorptive performance of mesoporous silica-based materials towards inorganic (metal ions) and organic (dyes) water pollutants was investigated. Mesoporous silica materials with different ...particle size, surface area and pore volume were prepared and tailored with different functional groups. These materials were then characterised by solid-state techniques, namely vibrational spectroscopy, elemental analysis, scanning electron microscopy and nitrogen adsorption-desorption isotherms, allowing the successful preparation and structural modifications of the materials to be confirmed. The influence of the physicochemical properties of the adsorbents towards the removal of metal ions (Ni
, Cu
and Fe
) and organic dyes (methylene blue and methyl green) from aqueous solutions was also investigated. The results reveal that the exceptionally high surface area and suitable ζ-potential of the nanosized mesoporous silica nanoparticles (MSNPs) seem to favour the adsorptive capacity of the material for both types of water pollutants. Kinetic studies were performed for the adsorption of organic dyes by MSNPs and large-pore mesoporous silica (LPMS), suggesting that the process follows a pseudo-second-order model. The recyclability along consecutive adsorption cycles and the stability of the adsorbents after use were also investigated, showing that the material can be reused. Current results show the potentialities of novel silica-based material as a suitable adsorbent to remove pollutants from aquatic matrices with an applicability to reduce water pollution.
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The porous metal-organic framework UiO-66(Zr) obtained via non modulated synthesis, has revealed to be a notable heterogeneous catalyst, enabling extremely fast and very efficient desulfurization of ...a multicomponent model diesel and also a real diesel fuel.
Graphene sheets, which possess unique nanostructure and a variety of fascinating properties, are considered as promising nanoscale building blocks of new nanocomposites, namely as a support material ...for the dispersion of metal nanoparticles. One of the methodologies used to prepare graphene sheets is the chemical exfoliation of graphite in aqueous medium, which produces oxygen functionalized graphene sheets. Here, we show that the presence of oxygen functionalities at the graphene surface provides reactive sites for the nucleation and growth of gold nanoparticles. Gold nanoparticles are effectively grown at functionalized graphene surfaces using a simple chemical method in aqueous medium. The nucleation and growth mechanism depends on the degree of oxygen functionalization at the graphene surface sheets, no gold nanoparticles are obtained at totally reduced graphene surfaces. Additionally, our studies indicate that the graphene/gold nanocomposites are potential substrates for SERS (surface enhanced Raman scattering) in particular for single gold nanoparticle SERS studies.
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•Keggin-type polyoxometalate structural modification was performed to achieve high oxidative desulfurization of diesel.•The active lacunar phosphotungstate was immobilized on ...different amine-SBA-15 supports to produce robust solid catalysts.•The PW11@aptesSBA-15 heterogeneous catalyst showed the best desulfurization performance.•PW11@aptesSBA-15 catalyst allowed complete desulfurization of a simulated diesel after only 1 h using a solvent-free system.•Real diesel (2300 ppm S) was oxidative desulfurized with 83% of efficiency after 2 hous.
Strategic polyoxometalate Keggin-type structural modification was performed to increase the oxidative catalytic performance to desulfurize model and real diesels. The most active lacunar structure PW11O397− (PW11) showed to complete desulfurize a simulated diesel after 60 min at 70 °C. Its application as homogeneous catalyst using a biphasic system 1:1 diesel/acetonitrile needed to use an excess of oxidant (ratio H2O2/S = 8). The immobilization of the PW11 on amine-functionalized SBA-15 supports originated two heterogeneous catalysts PW11@aptesSBA-15 and PW11@tbaSBA-15. The best results were attained with the PW11@aptesSBA-15 catalyst showing identical oxidative desulfurization performance as the homogeneous analogue. As advantage, this heterogeneous catalyst promotes the complete desulfurization of simulated diesel using a solvent-free system, i.e. without the need of acetonitrile use. On the other hand, the same desulfurization efficiency could be achieved using half the amount of oxidant (H2O2/S = 4). The oxidative desulfurization of the real diesel achieved a remarkable 83.4% of efficiency after just 2 h. The recycling capacity of PW11@aptesSBA-15 catalyst was confirmed for eight consecutive cycles using the biphasic and the solvent-free systems. Its stability investigation demonstrates to be higher under the solvent-free system than the biphasic system, without practically any occurrence of PW11 leaching in the first case. On the other hand, the Venturello peroxocomplex PO4{W(O2)2} 43−, recognized as active intermediate in the homogeneous biphasic system, was not identified in the heterogeneous catalytic systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
The highly active peroxomolybdate, TBA
3
{PO
4
MoO(O
2
)
2
4
}·3H
2
O (abbreviated as PMo
4
), was incorporated for the first time in various porous MOF support structures (MIL-101, MOF-808, and ...ZIF-8) to form heterogeneous catalysts with different structural properties. These catalysts were used to treat a multicomponent model diesel
via
an oxidative desulfurization process. Sulfur-free diesel could be obtained after only 2 h depending on the porous MOF structural morphology. The size of the window entrance and the dimension of the pore from the MOF support had a remarkable influence on the catalytic performance of PMo
4
@MOF catalysts, and thus, the conditioning of reactant diffusion. PMo
4
@MIL-101 presented the highest catalytic efficiency (100% after 2 h), followed by PMo
4
@MOF-808 (73.1% at 2 h) and PMo
4
@ZIF-8 (68.1% at 2 h). Furthermore, the most active catalyst, PMo
4
@MIL-101, showed remarkable recycle capacity and structural stability (maintaining the activity and stability for 10 catalytic cycles). Appropriate window and pore size cavities from MIL-101 support were the most suitable for organosulfur oxidation. Smaller windows and pore sizes from the other MOFs caused a decrease in catalytic efficiency. The windows and porous dimensions from MOF-based catalysts have a direct effect on catalyst performance, and these must be adjusted to reactants and active guest centers to avoid leaching and allow a fluent diffusion of reactants, mainly the ones with large molecular sizes.
The highly active peroxomolybdate, TBA
3
{PO
4
MoO(O
2
)
2
4
}·3H
2
O was incorporated for the first time in various porous MOF support structures (MIL-101, MOF-808, and ZIF-8) to form heterogeneous catalysts with different structural properties.
A correlation between polyoxotungstate structures and their catalytic performance for oxidative desulfurization processes was investigated. Bridged lanthanopolyoxometalates that incorporate identical ...metallic centers with Keggin- EuPW11O3911− and Lindqvist-type Eu(W5O18)29− structures were used as catalysts for the oxidation of the most representative refractory sulfur compounds. Both compounds were able to desulfurize a multicomponent model diesel under sustainable conditions, i.e., using ionic liquid as an extraction solvent and hydrogen peroxide as an oxidant. However, the Lindqvist catalyst appeared to achieve complete desulfurization faster than the Keggin catalyst while using a lesser amount of catalyst and oxidant. Furthermore, the reusable capacity of the Lindqvist-type Eu(W5O18)29− was confirmed for consecutive oxidative desulfurization processes. The contribution of the lanthanide metallic center for the catalytic performance of these compounds was investigated by studying the analogous TB(W5O18)29− compound. Identical desulfurization efficiency was obtained, even reusing this catalyst in consecutive reaction cycles. These results indicate that the active catalytic center of these compounds is probably related to the octahedral tungsten centers. However, a higher number of tungsten centers in the polyoxometalate structure did not result in higher catalytic activity.
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A novel composite has been prepared through the immobilization of the Keggin sandwich-type Sm(PMo11O39)211− 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 BMIMPF6 ionic liquid. The optimized extractive and catalytic oxidative desulfurization system (ECODS) with BMIMPF6 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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
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(PW 11 O 39 ) 2 11− polyoxometalate (POM) was supported on Al( iii ) and Cr( iii ) MIL-type MOFs, NH 2 -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.
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