This study explores deep eutectic solvents (DESs) as potential alternatives to dimethylformamide (DMF) for extractive desulfurization of gas oil and marine fuel oil. A series of DESs, based on choline chloride (ChCl) and tetrabutylammonium bromide (TBAB), were evaluated using straight-run gas oil (SRGO) and compared to DMF. The influence of an oxidation pre-treatment and water content was also investigated, and the most efficient systems were further applied to marine fuel oil. Firstly, oxidation was found to be essential to enhance sulfur removal by improving the extractability of sulfone compounds. The results show that DES formulation strongly affects desulfurization performance, with TBAB-based DESs achieving efficiencies comparable to DMF (~80% desulfurization rate) and outperforming ChCl-based systems. In ChCl-based DESs, a moderate water content (~10 wt%) improved performance, whereas higher amounts disrupted the hydrogen-bond network, as evidenced by Fourier-transform infrared spectroscopy, leading to a decreased efficiency. When applied to marine fuel oil, similar trends were observed, although lower desulfurization levels were obtained due to the complexity of the feed, and a solvent-to-fuel ratio of 5:1 was required for proper phase separation. Fourier transform mass spectrometry analyses highlighted the persistence of refractory sulfur species, emphasizing the need for tailored solvent design. Overall, DESs represent promising and adaptable alternatives for desulfurization processes.

Two-dimensional (2D) layered materials have attracted significant interest for catalytic applications due to tuneable electronic properties, and a high density of edge-active sites associated to a high proportion of reactant-accessible active sites. In this work, we report the synthesis of 2D/3D MoS2@Ni/SBA-15 heterostructure via thermal in situ gas-phase sulfidation of MoO3@NiO/SBA-15 precursor, aimed at promoting reverse water-gas shift (RWGS) reaction. Catalytic tests, conducted over a wide temperature range (200-800 degrees C) revealed that the MoS2@Ni/SBA-15 catalyst significantly outperforms its oxidic counterpart in terms of product selectivity, while both catalysts exhibit high CO2 conversion. Notably, the sulfided heterostructure achieves complete suppression of CH4 formation and maintains 100% selectivity towards CO across the entire temperature range studied. In contrast, MoO3@NiO/SBA-15 favours methanation at low temperatures and only shifts to CO production at T > 600 degrees C. At 500 degrees C, a CO2 conversion of 33.3% is achieved on MoS2@Ni/SBA-15 with exclusive CO selectivity, surpassing most state-of-the-art transition metal-based catalysts operating at similar conditions. Moreover, long-term stability tests at 800 degrees C, over 100 h, confirmed its remarkable stability, maintaining high CO2 conversion (>75%) and full CO selectivity without any visible deactivation. These results demonstrate the strong potential of engineered 2D/3D MoS2-based heterostructures as efficient, robust, and non-noble metal catalysts for sustainable CO2 valorisation.

Here, we report the dynamic transformation of few-layered MoS2 supported on mesoporous SBA-15 (FL-MoS2/SBA-15) into highly dispersed MoCx nanoclusters under reverse water-gas shift (RWGS) reaction conditions. Despite a low Mo loading (10 wt %), the in situ carburized catalyst achieves a high CO2 conversion of 63% at 600 °C, with complete CH4 suppression and exceptional CO selectivity (∼100%), significantly outperforming classical multilayer MoS2 (ML-MoS2) analogues and other references from the literature. Electron paramagnetic resonance (EPR) spectroscopy confirms a high density of sulfur vacancies in the FL-MoS2 precursor, which facilitates CO2 activation and promotes carburization reaction: under reaction conditions, carbon incorporation leads to the formation of these catalytically active and selective MoCx nanostructures, while conventional ML-MoS2 undergoes incomplete transformation. The resulting MoCx nanocluster catalyst shows excellent stability, maintaining 63% CO2 conversion and full CO selectivity over 100 h, at 600 °C and a WHSV of 12,000 mL/gcatal·h. These findings demonstrate the critical role of catalyst precursor nanostructure design and defect engineering in driving structural reactive transformations to achieve selective and stable catalysts.

The chalcogenide MoS2 has three polymorphs: 2 H; 3 R; 1 T. Each of them is endowed with interesting properties and characteristics which make them promising materials for photo- and electrocatalysis, photodevices and electronics. In this work, we demonstrate the impact of the chosen synthesis path in which molybdenum precursor is introduced on the formation of MoS2 on TiO2 nanotubes (TiNT) using FTIR spectroscopy. Thus,for the first time 1 T-MoS2 was obtained under H2S/H2 flow by incorporating Mo into the nanotube wall which might be an interesting approach for industrial scaling-up procedures. Moreover, unprecedently we report the possible detection of 1 T-MoS2 via IR-transmission using CO as a probe molecule.

The oxidative desulfurization (ODS) of heavy fuel oil (HFO) offers a promising solution for desulfurizing marine fuels under mild conditions, in line with current environmental regulations. While most studies focus on model or light fuels, explaining deactivation through leaching or sulfone adsorption, the deactivation mechanisms of catalysts in HFO remain poorly understood. In this work, Mo-based catalysts supported on alumina were extensively characterized before and after catalytic reactions, and regeneration through air calcination was considered. Techniques such as XRD, Raman spectroscopy, XRF, and TGA, alongside catalytic testing with H2O2 as an oxidant, revealed that Mo surface speciation significantly impacted both activity and deactivation. Contrary to well-dispersed polymolybdates, crystalline MoO3 induced low activity and hindered regeneration. No leaching of the active phase was demonstrated during the reaction. Sulfone adsorption had minimal impact on deactivation, while non-sulphur compounds appeared to be the key contributors. Regeneration outcomes were found to be molybdenum content-dependent: 10Mo/Al recovered its activity, while 20Mo/Al formed inactive phases, like Al2(MoO4)3. Using an organic oxidant (tBHP) during ODS influenced the regeneration, as it prevented Al2(MoO4)3 formation and redispersed crystalline MoO3, enhancing performance. These findings advance understanding of catalyst deactivation and suggest strategies to extend catalyst life in the ODS of HFO.

A series of unsupported mono- and bimetallic MonW12-nS2 catalysts were synthesized by alumina elimination from supported MonW12-nS2/Al2O3 samples using acid etching. Alumina supported catalysts have been in turn prepared by using monometallic H4SiMo12O40 and H4SiW12O40 heteropolyacids (HPAs), their mixture with Mo/W atomic ratio equal to 1/11 and 3/9, and mixed bimetallic H4SiMo1W11O40 and H4SiMo3W9O40 HPAs. All catalysts were characterized by N2 adsorption, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), extended X-ray absorption fine structure (EXAFS) spectroscopy and powder X-ray diffraction (XRD) and their performance were evaluated in simultaneous hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrogenation (HYD) of naphthalene. The etching process led to a successful removal of all the support and of the partially sulfided species, with sulfidation degrees of both Mo and W above 90 % on the final bulk solids. The active phase also underwent a rearrangement, as higher average length and stacking were measured on the bulk catalysts than on the original supported ones. Mixed MoWS2 phase was evidenced in all solids, prepared from mixed HPAs (MonW12-nS2) or from the mixture of monometallic HPAs (RefMonW12-nS2), by EXAFS and ToF-SIMS, with however a larger quantity on the MoW solids. It seems that the mixed MoWS2 phase observed on the supported MoW catalysts is maintained through the etching process, while on RefMonW12-nS2 the mixed phase, observed in a much lesser extent in the corresponding supported catalyst, could result from the aggregation of the monometallic slabs. MonW12-nS2 catalysts were found more effective than the monometallic catalysts and than the corresponding RefMonW12-nS2, in both dibenzothiophene hydrodesulfurization and naphthalene hydrogenation, which was related to the presence of the mixed phase maintained through the etching of the support.

Oxidative desulfurization (ODS) was applied to three marine fuels with viscosities between 380 and 700 cSt (centistokes) and sulfur contents between 0.79 and 3.27 wt.%, using a MoO3/Al2O3 catalyst. H2O2 was chosen as oxidizing agent with a low oxidant to sulfur ratio of 3, for economic and environmental reasons. Global sulfur removal was obtained after extraction of sulfones by dimethylformamide. Oxidation efficiency was evaluated by monitoring the conversion of alkyl-benzothiophenes and dibenzothiophene molecule by gas chromatography (GC) with a sulfur specific detector. Applying ultrasounds prior to oxidation was found to significantly enhance conversions and sulfur removal, the effect being more pronounced when initial efficiency was low, that is for more refractory molecules and heavier fuels. Ultrasound assisted ODS (UAOD) was effective on raw fuels with initial viscosity below 700 cSt. Indeed, dilution decreased the viscosity of the fuels, allowing reaction to be effective even on initially very heavy fuels. The presence of asphaltenes dissolved or precipitated in the feed did not affect the conversion of Cx-BTs and DBT significantly, with only slight variations of global sulfur removal rates. Global desulfurization rates between 60 and 80 % were obtained, clearly showing the efficiency of UAOD applied to complex matrices such as marine fuels.

New mixed H4[SiMonWn-12O40] (n = 6 and 9) Keggin type heteropolyacids (HPAs) have been successfully synthesized, as confirmed by single-crystal XRD, Raman and IR spectroscopy analysis. The resulting polyoxometallates were used for preparation of hydrotreatment catalysts. Mo(W)/Al2O3 catalysts were synthesized by incipient wetness impregnation of alumina support with water solutions of prepared mixed Keggin HPAs and corresponding counterparts based on mixture of monometallic H4[SiMo12O40] and H4[SiW12O40] HPAs. Oxidic catalysts were analyzed by Raman spectroscopy to determine the precursor structure after deposition. Catalysts in sulfided state were characterized by high-resolution transmission electron microscopy (HRTEM), high angle annular dark field imaging (HAADF) and X-ray photoelectron spectroscopy (XPS) and were tested in co-hydrotreating of dibenzothiophene (DBT) and naphthalene. The use of new mixed Keggin HPAs made it possible to obtain catalysts with mixed MoWS2 active centers, which was confirmed by HAADF. Moreover, the Mo/(Mo + W) ratio has a direct effect on the structure of the active phase species. An ordered core-shell structure with Mo atoms in the core is maintained until the fraction of molybdenum in mixed MoW/Al2O3 catalyst exceeds 50 %, where a more disordered structure is observed. Moreover, this Mo/(Mo + W) ratio of 0.5 is optimal to achieve a maximum catalytic activity. Indeed, the turnover frequencies (TOF) of the MoWS2 edge centers with random atoms distribution in a cluster as in Mo9W3/Al2O3, was lower compared to that of Mo6W6/Al2O3 with core-shell structure.

Trimetallic NiMoW/Al2O3 catalysts based on mixed H-4[SiMonWn-12O40] (n = 1, 3, 6, and 9) Keggin-type heteropolyacids (HPAs) were synthesized by incipient wetness impregnation of alumina with aqueous solutions of mixed HPAs. For comparison purposes, trimetallic samples were prepared from a mixture of monometallic H-4[SiMo12O40] and H-4[SiW12O40] HPAs with a Mo/W ratio corresponding to the mixed MoW HPAs. The catalysts were sulfided by a liquid phase method and tested in the model reactions of dibenzothiophene hydrodesulfurization and naphthalene hydrogenation, with subsequent addition of quinoline to study the effect of inhibition of target reactions. Further, the catalysts were tested in the hydrotreating of straight-run gas oil to evaluate the efficiency of catalysts on real feedstocks. In order to link catalytic performances with the preparation method and Mo/W ratio, the catalysts were fully characterized by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, high-angle annular dark-field imaging, and quick X-ray absorption spectroscopy. It was found that the Mo/W atomic ratio of the structure-forming metals in the active phase, deriving from the Mo/W ratio in the HPA precursor, directly affects the ratio of the hydrogenation and hydrodesulfurization performances. For feedstock with a high concentration of N-containing compounds, it is necessary to use mixed NiMoW systems with a high tungsten percentage to reduce the inhibitory effect and ensure the quality of the products. The use of new mixed MoW Keggin HPAs has made it possible to enhance the synergistic effect in trimetallic NiMoW catalysts due to the closer interaction between Mo and W, which increased the sulfidation degree of metals and also contributed to the formation of highly active mixed NiMoWS sites. (C) 2021 Elsevier Inc. All rights reserved.

Bimetallic catalysts MoW/СОK-12 are synthesized on the basis of mesostructured silicate COK‑12 prepared from sodium silicate aqueous solution using the Keggin structure hetero polyacid H 4 Si-Mo 3 W 9 O 40 as an oxide precursor of the sulfide active phase and with the use of the mechanical mixture of two monometallic hetero polyacids (H 4 SiMo 12 O 40 and H 4 SiW 12 O 40 ) at a molar ratio of Mo/W = 3/9. Alumina-based analogs with the same surface metal content are used as reference samples. The test samples are analyzed by low-temperature nitrogen adsorption and high-resolution transmission electron microscopy. The catalytic activity is studied in the combined hydrotreatment of dibenzothiophene and naphthalene and in the hydrodesulfurization of 4,6-dimethyldibenzothiophene in a flow unit. It is shown that the use of mesostructured silicate COK-12 as a support leads to an increase in catalytic activity in target hydrotreating reactions.

Alumina supported MoW hydrotreating catalyst was synthesized by using bimetallic H-4[SiMo3W9O40] Keggin heteropolyacid (HPA). Catalysts based on monometallic H-4[SiMo3W9O40] and H-4[SiMo3W9O40] and their mixture were also studied. Genesis of the active phase was studied during atmospheric gas sulfidation by H2S/H-2 of the catalysts by in-situ Quick X-ray absorption spectroscopy (XAS) and High-Angle Annular Dark-Field (HAADF) imaging. The combination of different chemometric tools such as Principal Component Analysis (PCA) and Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) allowed to determine the number of intermediate species, their chemical nature and concentration profiles during sulfidation. It was found that tungsten sulfidation using bimetallic HPA precursor started at lower temperature, compared to W sulfidation in the monometallic and in the mixture of monometallic HPA catalysts. Simultaneous sulfidation of Mo and W atoms in case of the bimetallic molecular precursor can govern the formation of mixed MoWS2 phase, which formation during activation was evidenced by HAADF.

The catalytic properties of trimetallic NiMoWS catalysts supported on alumina are studied in the process of straight-run diesel fraction hydrotreating. It is shown that the nature of the oxide precursor of the mixed NiMoWS active phase strongly affects catalyst activity in the hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and hydrogenation (HYD) of polycyclic aromatic hydrocarbons (PAH). The NiMoWS/Al2O3 catalyst synthesized from the mixed H4SiMo3W9O40 heteropoly acid is more efficient than the sample prepared from a mixture of individual H4SiMo12O40 and H4SiW12O40 heteropoly acids in both HDS and HDN transformations at the same metal content. The highest activity in PAH hydrogenation is exhibited by the NiMoWS/Al2O3 catalyst prepared using H4SiMo3W9O40.

A bulk MoWS2 catalyst has been synthesized by acid etching of the carrier from the supported MoWS2/Al2O3 catalyst obtained on the basis of the mixed bimetallic heteropoly acid (HPA) H4[SiMo3W9O40]. As reference samples, monometallic MoS2 and WS2 catalysts have been prepared from the corresponding supported analogues, as well as a Mo + WS2 sample based on a mechanical mixture of monometallic HPA in the atomic ratio of Mo/W = 1/3. The catalytic properties of the synthesized catalysts have been studied in model reactions of hydrodesulfurization (HDS) of dibenzthiophene (DBT) and hydrogenation (HYD) of naphthalene in a flow unit. It has been shown that the catalytic activity of the samples in both the DBT HDS and naphthalene HYD reactions increases in the following order: MoS2 < WS2 < Mo + WS2$$ \ll $$ MoWS2. It has been found that the bulk tungsten-containing catalysts exhibit higher specific catalytic activity than the supported counterparts. Increased values of hydrogen uptake according to the results of hydrogen temperature-programmed reduction for the bulk catalysts indicate an increase in the number of active sites and the formation of a more effective active phase compared to supported catalysts.

Mo(W)/SBA-15 catalysts are prepared using heteropoly acids H4SiMo12O40, H4SiW12O40, and H4SiMo3W9O40. The catalysts in the sulfide form are studied by low-temperature nitrogen adsorption, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Catalytic properties are tested in the hydrodesulfurization of 4,6-dimethyldibenzothiophene. It is shown that the gas-phase sulfiding of Mo(W)/SBA-15 catalysts leads to increase in the average length of particles and the number of Mo(W)S2 layers in active phase particles compared with liquid-phase sulfiding with the use of dimethyl sulfide. The replacement of a quarter of tungsten atoms with molybdenum ones makes it possible to considerably improve the catalytic activity of the mixed catalyst Mo + W/SBA-15 compared with the monometallic counterparts. This effect can be enhanced due to the use of mixed heteropoly acid H4SiMo3W9O40 as a precursor of the active phase of the MoW/SBA-15 catalyst, which is apparently associated with the formation of MoWS2 active sites.