Fátima Mirante

An organic–inorganic hybrid material of the MoO ₃ /organonitrogen ligand class, formulated as [MoO ₃ (bpm)] ( 2 ) (bpm = bis(pyrazolyl)methane), has been prepared under mild conditions by the hydrolysis of the complex [MoO ₂ Cl ₂ (bpm)] ( 1 ). Polymeric 2 was used in the extractive and catalytic oxidative desulfurization (ECODS) of a model diesel under sustainable conditions, with H ₂ O ₂ as oxidant and ethanol as extraction solvent, achieving near‐quantitative elimination of 1‐benzothiophene, dibenzothiophene, 4‐methyldibenzothiophene, and 4,6‐dimethyldibenzothiophene after 2 h. The activity was largely retained for several desulfurization cycles. Characterization of species isolated from the treatment of 2 with H ₂ O ₂ in ethanol indicated a catalytic process involving the in situ formation of the homogeneous catalyst [MoO(O ₂ ) ₂ (bpm)] which is retained in the extraction phase. Application of the ECODS system to a real diesel (1335 ppm S) led to a sulfur removal of 54%. When the ionic liquid [BMIM][PF ₆ ] was employed as the extraction solvent (BMIM = 1‐butyl‐3‐methylimidazolium), the quantitative elimination of S compounds from the model fuel was achieved within 2 h. In recycling experiments, loss of activity due to the accumulation and precipitation of sulfones could be nullified by their removal between cycles, allowing the catalyst/[BMIM][PF ₆ ] phase to be used for at least five cycles without loss of desulfurization efficiency.

MIL-101-SO ₃ H and UiO-66-(COOH) ₂ are effective in the valorization of glycerol into solketal fuel additive through a sustainable catalytic process.

The development of sustainable catalysts from renewable resources is a key challenge for reducing the cost of industrial catalytic processes and waste valorization. In this work, low-cost heterogeneous active catalysts were prepared based on pyrolyzed forest residues, forming valuable porous support materials (Biochar) able to efficiently accommodate the highly active heteropolyacid HPW₁₂. Further, magnetic functionality was incorporated in the novel catalytic materials by the impregnation of NiFe₂O₄. The resulting magnetic composites were characterized by FTIR-ATR, SEM-EDS, ICP-OES, BET, XRD, potentiometric titration and magnetometry. The novel HPW₁₂@NiFe₂O₄@Biochar composites were able to valorize the glycerol to produce the fuel additive solketal with high conversion and high selectivity after only 3 h of reaction via acetalization reaction with acetone. The biochar catalytic composite prepared from cork presented higher pore size than the same prepared from forest biomass. This property was crucial to achieve the best conversion (89%) and the highest solketal selectivity (96%). Additionally, reusability capacity was verified, supporting the potential of the cork-pyrolyzed-based composites as potential low-cost catalytic material to produce fuel additives, such as solketal, under sustainable conditions. This may contribute one step further toward a future with greener energy, increasing the viability of biodiesel industry waste.

Following the success of the first edition, this second volume of the Special Issue “Designing Catalytic Desulfurization Processes to Prepare Clean Fuels” brings more advanced and innovative strategies for the removal of sulfur compounds from fuels

Sulfur compounds in fuels are the primary causes of acid rain and environmental pollution

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.

The composites of heteropolyacids (H₃PW₁₂, H₃PMo₁₂) incorporated into amine-functionalized silica materials were used for the first time as heterogeneous catalysts in the valorization of glycerol (a major waste from the biodiesel industry) through acetalization reaction with acetone. The polyoxotungstate catalyst H₃PW₁₂@AptesSBA-15 exhibited higher catalytic efficiency than the phosphomolybdate, achieving 97% conversion and 97% of solketal selectivity, after 60 min at 25 °C, or 91% glycerol conversion and the same selectivity, after 5 min, performing the reaction at 60 °C. A correlation between catalytic performance and catalyst acidity is presented here. Furthermore, the stability of the solid catalyst was investigated and discussed.

A dioxomolybdenum catalyst [(MoO2Cl2-O-MoO2Cl2)(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 showed 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, occurring the oxidation of the sulfur compounds in the polar organic solvent. The oxidative catalytic performance of (1) showed 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.

The composites of heteropolyacids (H3PW12, H3PMo12) incorporated into amine-functionalized silica materials, were used for the first time as heterogeneous catalysts in the valorisation of glycerol (a large waste from biodiesel industry) by acetalization reaction with acetone. The polyoxotungstate catalyst H3PW12@AptesSBA-15 presented higher catalytic efficiency than the phosphomolybdate, with 97% of conversion with 97% of solketal selectivity, after 60 min at 25 °C, or 91% of glycerol conversion and the same selectivity, after 5 min, performing the reaction at 60 ºC. A relation of catalytic performance and acidity of the catalyst is here presented. Furthermore, the stability of the solid catalyst was investigated and discussed.