Binuclear Dioxomolybdenum(VI) Complex Based on Bis(2-pyridinecarboxamide) Ligand as Effective Catalyst for Fuel Desulfurization

Funding Information: The authors acknowledge ChiraTecnics ( http://www.chiratecnics.com ) for the supply of the chiral diamine ligand used to generate the Mo catalyst. Authors thank Anthony Burke (University of Coimbra) and Isabel S. Gon\u00E7alves (CICECO, University of Aveiro) for valuable discussions on catalyst formation and behaviour. Publisher Copyright: © 2024 by the authors.A binuclear dioxomolybdenum catalyst [(MoO2Cl2)2(L)] (1) (with L (1S,2S)-N,N′-bis(2-pyridinecarboxamide)-1,2-cyclohexane) was prepared and used as catalyst for the desulfurization of a multicomponent model fuel containing the most refractory sulfur compounds in real fuels. This complex was shown to have a high efficiency to oxidize the aromatic benzothiophene derivative compounds present in fuels, mainly using a biphasic 1:1 model fuel/MeOH system. This process conciliates catalytic oxidative and extractive desulfurization, resulting in the oxidation of the sulfur compounds in the polar organic solvent. The oxidative catalytic performance of (1) was shown to be influenced by the presence of water in the system. Using 50% aq. H2O2, it was possible to reuse the catalyst and the extraction solvent, MeOH, during ten consecutive cycles without loss of desulfurization efficiency.publishersversionpublishe

Desulfurization of liquid fuels by extraction and sulfoxidation using H2O2 and [CpMo(CO)3R] as catalysts

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.publishe

A sustainable peroxophosphomolybdate/H2O2 system for the oxidative removal of organosulfur compounds from simulated and real high-sulfur diesels

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.publishe

Easy and Fast Production of Solketal from Glycerol Acetalization via Heteropolyacids

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

Recent Advances in Catalytic Compounds Developed by Thermal Treatment of (Zr-Based) Metal–Organic Frameworks

Metal–organic frameworks (MOFs) have been the subject of extensive scientific investigation in the last three decades and, currently, they make up one of the types of compounds most studied for their potential application in a wide range of distinct catalytic processes. Pristine MOF compounds provide several intriguing benefits for catalytic applications, including large interior surface areas and high densities of active sites; high catalytic reaction rates per volume; post-synthesis modifications with complementary catalytic groups; and the ability for multiple functional groups to catalyze the reaction. For most large-scale catalytic applications, including those in fuel processing, gas emission reduction, and chemical synthesis, pristine MOFs often show limited stabilities and opportunities for regeneration at high temperatures. As a result, the real applications of MOFs in these technologies are likely to be constrained, and a controlled thermal modification to prepare MOF-derivative compounds has been applied to induce crystalline structural changes and increase the structural stability of the MOFs, enhancing their potential applicability in more severe catalytic processes. Recent advances concerning the use of this strategy to boost the catalytic potential of MOF-derivative compounds, particularly for stable Zr-based MOFs, are outlined in this short review article

Polyoxomolybdate based ionic-liquids as active catalysts for oxidative desulfurization of simulated diesel

This work was partly funded through the Associate Laboratory for Green Chemistry- LAQV which is financed by national funds from FCT/MCTES (POCI-01-0145-FEDER-007265, UID/QUI/50006/2019) and CENIMAT, I3N (POCI-01-0145-FEDER-007688, UID/CTM/50025/2013), also financed by national funds through the FCT/MCTES, and when appropriate co-financed by the Fundo Europeu de Desenvolvimento Regional (FEDER) under the PT2020 Partnership Agreement. This work is funded by national funds (OE), through FCT – Fundação para a Ciência e a Tecnologia. European Social Fund through the program POPH of QREN. The authors also acknowledge the Portuguese Nuclear Magnetic Resonance Network (PTNMR).This work compares the stability and the catalytic efficiency of different ionic liquid phosphomolybdates ([BPy]3[PMo12O40] and [BMIM]3[PMo12O40]) with a cationic (propylpyridinium) functionalized mesoporous silica nanoparticle composite (PMo12O40@PPy-MSN). These were used as solid catalysts for the oxidative desulfurization of a multicomponent model diesel using hydrogen peroxide as oxidant and a polar immiscible extraction solvent. Ionic liquid ([BMIM][PF6] was successfully used as solvent to extract sulfur compounds from model diesel. The ionic liquid phosphomolybdates showed partial solubility in the ionic liquid phase, occurring some decomposition of their Keggin structure in the soluble reaction media, probably caused by their interaction with oxidant. On the other hand, the phosphomolybdate composite PMo12O40@PPy-MSN presented high structural stability and only negligible leaching occurrence after various consecutive reaction cycles. The model diesel was near complete desulfurized after 3 h and consecutive desulfurization cycles were performed without loss of activity. Therefore, the immobilization of Keggin phosphomolybdate structure [PMo12O40]3− using cationic propylpyridinium silica nanoparticle is an assertive strategy to produce stable and active heterogeneous catalysts.authorsversionpublishe

Polyoxomolybdate based ionic-liquids as active catalysts for oxidative desulfurization of simulated diesel

This work was partly funded through the Associate Laboratory for Green Chemistry- LAQV which is financed by national funds from FCT/MCTES (POCI-01-0145-FEDER-007265, UID/QUI/50006/2019) and CENIMAT, I3N (POCI-01-0145-FEDER-007688, UID/CTM/50025/2013), also financed by national funds through the FCT/MCTES, and when appropriate co-financed by the Fundo Europeu de Desenvolvimento Regional (FEDER) under the PT2020 Partnership Agreement. This work is funded by national funds (OE), through FCT – Fundação para a Ciência e a Tecnologia. European Social Fund through the program POPH of QREN. The authors also acknowledge the Portuguese Nuclear Magnetic Resonance Network (PTNMR).This work compares the stability and the catalytic efficiency of different ionic liquid phosphomolybdates ([BPy]3[PMo12O40] and [BMIM]3[PMo12O40]) with a cationic (propylpyridinium) functionalized mesoporous silica nanoparticle composite (PMo12O40@PPy-MSN). These were used as solid catalysts for the oxidative desulfurization of a multicomponent model diesel using hydrogen peroxide as oxidant and a polar immiscible extraction solvent. Ionic liquid ([BMIM][PF6] was successfully used as solvent to extract sulfur compounds from model diesel. The ionic liquid phosphomolybdates showed partial solubility in the ionic liquid phase, occurring some decomposition of their Keggin structure in the soluble reaction media, probably caused by their interaction with oxidant. On the other hand, the phosphomolybdate composite PMo12O40@PPy-MSN presented high structural stability and only negligible leaching occurrence after various consecutive reaction cycles. The model diesel was near complete desulfurized after 3 h and consecutive desulfurization cycles were performed without loss of activity. Therefore, the immobilization of Keggin phosphomolybdate structure [PMo12O40]3− using cationic propylpyridinium silica nanoparticle is an assertive strategy to produce stable and active heterogeneous catalysts.authorsversionpublishe

Lindqvist versus Keggin-Type Polyoxometalates as Catalysts for Effective Desulfurization of Fuels

A correlation between polyoxotungstate structures and their catalytic performance for oxidative desulfurization processes was investigated. Bridged lanthanopolyoxometalates that incorporate identical metallic centers with Keggin- Eu[PW11O39]11− and Lindqvist-type [Eu(W5O18)2]9− 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)2]9− 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)2]9− 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

Improving the Catalytic Performance of Keggin [PW12O40]3− for Oxidative Desulfurization: Ionic Liquids versus SBA-15 Composite

Different methodologies were used to increase the oxidative desulfurization efficiency of the Keggin phosphotungstate [PW12O40]3− (PW12). One possibility was to replace the acid proton by three different ionic liquid cations, forming the novel hybrid polyoxometalates: [BMIM]3PW12 (BMIM as 1-butyl-3-methylimidazolium), [BPy]3PW12 (BPy as 1-butylpyridinium) and [HDPy]3PW12 (HDPy as hexadecylpyridinium. These hybrid Keggin compounds showed high oxidative desulfurization efficiency in the presence of [BMIM]PF6 solvent, achieving complete desulfurization of multicomponent model diesel (2000 ppm of S) after only 1 h, using a low excess of oxidant (H2O2/S = 8) at 70 °C. However, their stability and activity showed some weakness in continuous reused oxidative desulfurization cycles. An improvement of stability in continuous reused cycles was reached by the immobilization of the Keggin polyanion in a strategic positively-charged functionalized-SBA-15 support. The PW12@TM–SBA-15 composite (TM is the trimethylammonium functional group) presented similar oxidative desulfurization efficiency to the homogeneous IL–PW12 compounds, having the advantage of a high recycling capability in continuous cycles, increasing its activity from the first to the consecutive cycles. Therefore, the oxidative desulfurization system catalyzed by the Keggin-type composite has high performance under sustainable operational conditions, avoids waste production during recycling and allows catalyst recovery