Literatura académica sobre el tema "Bulk MoWS catalyst"

The structure and elementary composition of various commercial Fe-based MOFs used as precursors for Fischer–Tropsch synthesis (FTS) catalysts have a large influence on the high-temperature FTS activity and selectivity of the resulting Fe on carbon composites. The selected Fe-MOF topologies (MIL-68, MIL-88A, MIL-100, MIL-101, MIL-127, and Fe-BTC) differ from each other in terms of porosity, surface area, Fe and heteroatom content, crystal density and thermal stability. They are re-engineered towards FTS catalysts by means of simple pyrolysis at 500 °C under a N₂ atmosphere and afterwards characterized in terms of porosity, crystallite phase, bulk and surface Fe content, Fe nanoparticle size and oxidation state. We discovered that the Fe loading (36–46 wt%) and nanoparticle size (3.6–6.8 nm) of the obtained catalysts are directly related to the elementary composition and porosity of the initial MOFs. Furthermore, the carbonization leads to similar surface areas for the C matrix (S_BET between 570 and 670 m² g⁻¹), whereas the pore width distribution is completely different for the various MOFs. The high catalytic performance (FTY in the range of 1.9–4.6 × 10⁻⁴ mol_CO g_Fe⁻¹ s⁻¹) of the resulting materials could be correlated to the Fe particle size and corresponding surface area, and only minor deactivation was found for the N-containing catalysts. Elemental analysis of the catalysts containing deliberately added promoters and inherent impurities from the commercial MOFs revealed the subtle interplay between Fe particle size and complex catalyst composition in order to obtain high activity and stability next to a low CH₄ selectivity.

Metal-organic frameworks (MOFs) have attracted much attention since their discovery and have potential applications in many fields, including gas storage, separation, catalysis, and thermal energy conversion, due to their unique high porosity structure, tunable pore size, and functionalizability. Nano-sized MOFs (NMOFs) possessed both the properties of conventional bulk MOFs and additional physical/chemical properties because of their nanometer size, and thus can exhibit even better performance than related conventional bulk MOFs. In this paper, we introduced the development of NMOFs and presented several classical NMOFs structures and their applications. It also focused on the preparation methods and applications of some important NMOFs in recent years, and provided an outlook on the applications of NMOFs in novel material fields and their development perspective.

Nitro group reduction is a reaction of a considerable importance for the preparation of bulk chemicals and in organic synthesis. There are reports in the literature showing that incorporation of metal nanoparticles (MNPs) inside metal–organic frameworks (MOFs) is a suitable strategy to develop catalysts for these reactions. Some of the examples reported in the literature have shown activity data confirming the superior performance of MNPs inside MOFs. In the present review, the existing literature reports have been grouped depending on whether these MNPs correspond to a single metal or they are alloys. The final section of this review summarizes the state of the art and forecasts future developments in the field.

The sizes of rod-shaped bulk MOFs could be decreased to the nanoscale via using metal oxides as precursors, and then the as-obtained nanosized MOFs could be self-assembled to form urchin-shaped superstructure MOFs via changing the dosage of ligands.

Abstract New composite materials containing metal-organic framework (MOF-5) particles were manufactured by 3D printing. The optimal composition of the photopolymer formulation and printing conditions ensuring the highest quality of printing were selected. Retention of the metal-organic framework (MOF) structure in the resulting composite objects was demonstrated by powder X-ray diffraction. The distribution of MOF-5 particles over the whole bulk of the 3D product was studied by X-ray computed tomography. In the future, composite materials of this type containing catalytically active MOFs, with their structure and properties being controllable at the micro and macro levels, could find application as catalysts of various chemical processes.

AbstractNanoporous solids are ubiquitous in chemical, energy, and environmental processes, where controlled transport of molecules through the pores plays a crucial role. They are used as sorbents, chromatographic or membrane materials for separations, and as catalysts and catalyst supports. Defined as materials where confinement effects lead to substantial deviations from bulk diffusion, nanoporous materials include crystalline microporous zeotypes and metal–organic frameworks (MOFs), and a number of semi-crystalline and amorphous mesoporous solids, as well as hierarchically structured materials, containing both nanopores and wider meso- or macropores to facilitate transport over macroscopic distances. The ranges of pore sizes, shapes, and topologies spanned by these materials represent a considerable challenge for predicting molecular diffusivities, but fundamental understanding also provides an opportunity to guide the design of new nanoporous materials to increase the performance of transport limited processes. Remarkable progress in synthesis increasingly allows these designs to be put into practice. Molecular simulation techniques have been used in conjunction with experimental measurements to examine in detail the fundamental diffusion processes within nanoporous solids, to provide insight into the free energy landscape navigated by adsorbates, and to better understand nano-confinement effects. Pore network models, discrete particle models and synthesis-mimicking atomistic models allow to tackle diffusion in mesoporous and hierarchically structured porous materials, where multiscale approaches benefit from ever cheaper parallel computing and higher resolution imaging. Here, we discuss synergistic combinations of simulation and experiment to showcase theoretical progress and computational techniques that have been successful in predicting guest diffusion and providing insights. We also outline where new fundamental developments and experimental techniques are needed to enable more accurate predictions for complex systems.

Metal-organic framework (MOF) is attractive because of its representation as a class of crystalline porous materials with excellent properties, specifically its chemical functionality and high porosity, making it potentially tailored for various desired applications. Although the synthesis of MOFs have been well-documented, most reports are in the bulk and micrometer sizes. The synthesis of MOFs in the smaller size is still inevitable. This work reports the synthesis of nano MOF particles (i.e., MIL-100(Fe), HKUST-1(Cu), Cu-TPA, and MOF-5(Zn)). In the experiment, MOFs were created by interacting ligands and metal ions in the specific solvent in the solvothermal process. Different from other reports, this study used low concentrations of ligands and metal ions, in which this is effective to control ligand-metal ion interaction, reaction, nucleation, and growth of MOF. The successful synthesis was obtained and effective for various MOF particles by changing types of ligands and metal ions. The study also obtained that compatibility and dilution of the ligands and the metal ions in the specific solvent are important parameters. This information will bring new strategies and further developments for the synthesis of MOF materials for wider range of potential applications in separation, catalysis, dye adsorption, and drug carrier uses.

Metal–organic frameworks (MOFs) could be utilized for a wide range of applications such as sorption, catalysis, chromatography, energy storage, sensors, drug delivery, and nonlinear optics. However, to date, there are very few examples of MOFs exploited on a commercial scale. Nevertheless, progress in MOF-related research is currently paving the way to new industrial opportunities, fostering applications and processes interconnecting fundamental chemistry with engineering and relevant sectors. Yet, the fabrication of porous MOF materials within resistant structures is a key challenge impeding their wide commercial use for processes such as adsorptive separation. In fact, the integration of nano-scale MOF crystallic structures into bulk components that can maintain the desired characteristics, i.e., size, shape, and mechanical stability, is a prerequisite for their wide practical use in many applications. At the same time, it requires sophisticated shaping techniques that can structure nano/micro-crystalline fine powders of MOFs into diverse types of macroscopic bodies such as monoliths. Under this framework, this review aims to bridge the gap between research advances and industrial necessities for fostering MOF applications into real life. Therefore, it critically explores recent advances in the shaping and production of MOF macro structures with regard to the binding materials that have received little attention to date, but have the potential to give new perspectives in the industrial applicability of MOFs. Moreover, it proposes future paths that can be adopted from both academy and industry and can further boost MOF exploitation.

Metal organic frameworks (MOFs) have gained remarkable interest in water treatment due to their fascinating characteristics, such as tunable functionality, large specific surface area, customizable pore size and porosity, and good chemical and thermal stability. However, MOF particles tend to easily agglomerate in nanoscale, thus decreasing their activity and processing convenience. It is necessary to shape MOF nanocrystals into maneuverable structures. The in situ growth or ex situ incorporation of MOFs into inexpensive and abundant cellulose-family materials can be effective strategies for the stabilization of these MOF species, and therefore can make available a range of enhanced properties that expand the industrial application possibilities of cellulose and MOFs. This paper provides a review of studies on recent advances in the application of multi-dimensional MOF–cellulose composites (e.g., aerogels, membranes, and bulk materials) in wastewater remediation (e.g., metals, dyes, drugs, antibiotics, pesticides, and oils) and water regeneration by adsorption, photo- or chemocatalysis, and membrane separation strategies. The advantages brought about by combining MOFs and cellulose are described, and the performance of MOF–cellulose is described and compared to its counterparts. The mechanisms of relative MOF–cellulose materials in processing aquatic pollutants are included. Existing challenges and perspectives for future research are proposed.

Les raffineurs doivent faire face au renforcement des exigences environnementales relatives à la teneur en soufre des carburants ainsi qu'à l'utilisation de pétrole brut plus lourd pour la production de carburants à l'aide de procédés catalytiques d'hydrotraitement. Une des approches pour améliorer l'activité catalytique est le développement de sulfures trimétalliques NiMoW. Sur des catalyseurs supportés sur alumine, l'utilisation de précurseurs mixtes, les hétéropolyacides (HPA) de Keggin H4SiMo1W11O40 et H4SiMo3W9O40, s'est avérée plus favorable à la formation d'une phase MoWS mixte hautement active que le mélange de deux précurseurs monométalliques H4SiMo12O40 et H4SiW12O40. Dans cette étude, un nouveau protocole pour la synthèse de précurseurs mixtes H4SiMonW12-nO40 avec n = 6 et 9 a été développé. Ces nouveaux composés ont été caractérisés par spectroscopie IR et Raman, ainsi que par DRX sur monocristal. Des catalyseurs d'hydrotraitement massiques et supportés ont été synthétisés à partir de cette série d’HPA. Concernant les catalyseurs non promus supportés sur alumine, l'influence du rapport atomique Mo/(Mo+W) sur la composition de la phase active a été étudié ainsi que son effet sur l'activité catalytique dans des réactions d'hydrotraitement de composés modèles (hydrodésulfuration du dibenzothiophène et hydrogénation du naphtalène). Il a été observé par HAADF que pour un rapport atomique Mo/(Mo+W) égal à 0,25 et 0,5, la structure de la phase active après sulfuration en phase gaz est une structure core-shell. Une augmentation de la teneur en molybdène jusqu'à un ratio Mo/(Mo+W) de 0,75 conduit à une structure désordonnée de la phase active, correspondant à une diminution de l'activité catalytique. En revanche, pour les catalyseurs obtenus à partir d'un mélange des HPA monométalliques, la phase active s’est avérée principalement constituée de cristallites monométalliques MoS et WS, quel que soit le rapport atomique Mo/(Mo+W), avec une activité inférieure à celle des catalyseurs préparés à partir de HPA mixtes.L'influence du rapport atomique Mo/(Mo+W) pour les systèmes promus au nickel, après sulfuration en phase liquide afin de se rapprocher au maximum des conditions industrielles, a également été étudiée. L'introduction de Ni n'empêche pas la formation de la phase active mixte MoWS, ce qui a été confirmé par HAADF et EXAFS. De plus, l’effet d’inhibition dû à la présence de composés azotés dans la charge à hydrotraiter a été analysé. Il a été observé que les catalyseurs NiMoW/Al2O3 riches en tungstène sont plus résistants à la présence des composés azotés et que le choix de la composition du catalyseur doit être adapté selon la composition de la charge traitée.La dissolution par acide du support alumine a permis d'obtenir à partir d'échantillons sulfurés MonW12-n/Al2O3 des catalyseurs massiques MoWS avec une concentration en phase active supérieure à 90%. Des analyses par ToF-SIMS et EXAFS ont montré que la phase MoWS2 mixte est présente à la fois dans les catalyseurs synthétisés à partir des HPA mixtes et dans les échantillons obtenus à partir du mélange de deux HPA. Cependant, la concentration en sulfures mixtes dans le premier cas est beaucoup plus élevée, du fait que des cristallites mixtes étaient déjà présentes dans le solide supporté, alors que dans le cas du mélange des deux HPA, une phase mixte se forme à la suite du frittage des particules lors de la re-sulfuration. La concentration élevée en sulfures mixtes a permis d’obtenir une activité plus élevée des catalyseurs dans des réactions modèles.Enfin, le remplacement de l'alumine par une silice mésostructurée a permis d'augmenter l'activité des catalyseurs MoW non promus. Cependant, les valeurs similaires du degré de sulfuration, de la dispersion ainsi que des résultats des tests catalytiques entre les catalyseurs obtenus à partir des deux types de précurseurs semblent indiquer que la formation de phase mixte MoWS ne se produit pas sur ce type de support
Refiners have to face the strengthening of environmental requirements for the sulfur content in fuels together the use of heavier crude oil for producing market fuels using hydrotreatment catalytic processes. One of the approaches to improve catalytic activity is the development of bulk and supported ternary NiMoW sulfide catalysts following the recent introduction of industrial mixed bulk NiMoW catalysts NEBULA and Celestia. Previously, for supported alumina catalysts, the use of mixed precursors, H4SiMo1W11O40 and H4SiMo3W9O40 Keggin heteropyacids, has shown a better positive effect on the formation of a highly active mixed MoWS phase than the use of two corresponding monometallic H4SiMo12O40 and H4SiMo12O40 precursors. In this study, a new protocol for the synthesis of mixed Keggin-type H4SiMonW12-nO40 precursors with n = 6 and 9 has been developed. The new compounds were characterized by IR and Raman spectroscopy, as well as single-crystal XRD. Bulk and supported hydrotreating catalysts based on the whole series of H4SiMonW12-nO40 HPAs were synthesized. The influence of the atomic Mo/(Mo+W) ratio on the composition and structure of the active phase and its effect on the catalytic activity of unpromoted alumina supported catalysts in model hydrotreating reactions (hydrodesulfurization of dibenzothiophene and hydrogenation of naphthalene) were studied in detail. It was found that for an atomic Mo/(Mo+W) ratio equal to 0.25 and 0.5, the structure of the active phase under gas-phase sulfidation conditions is a core-shell structure, according to HAADF. A further increase in the molybdenum content up to 0.75 leads to disordering of the active phase structure, which has a negative effect on the catalytic activity. In contrast, for the catalysts obtained from a mixture of monometallic H4SiMo12O40 and H4SiMo12O40 HPAs, the active phase consisted mainly of monometallic MoS2 and WS2 crystallites, regardless of the atomic Mo/(Mo+W) ratio, as a result of which the catalysts showed lower activity compared to the samples prepared from mixed HPAs.The study of the influence of atomic Mo/(Mo+W) ratio for Ni-promoted systems, under the liquid-phase sulfidation in order to be as close as possible to industrial conditions, is also reported. It was shown that the introduction of Ni does not prevent the formation of a mixed MoWS active phase, which was confirmed by HAADF and EXAFS. Moreover, testing in the presence of a nitrogen-containing component made it possible to further study the inhibition on catalytic reactions. It was found that tungsten-rich NiMoW/Al2O3 catalysts are more resistant to the action of nitrogen-containing compounds indicating that the choice of the catalyst composition should be adapted to the composition of the processed feedstock.The use of acid (HF) etching of the alumina support made it possible to obtain from sulfided MonW12-n/Al2O3 samples bulk MoWS catalysts with an active phase concentration of more than 90%. ToF-SIMS and EXAFS showed that the mixed MoWS2 phase is present both in the catalysts synthesized from the mixed HPAs and in the samples obtained from the mixture of two HPAs. However, the concentration of mixed sulfides in the first case is much higher, due to the fact that mixed crystallites have already been formed, whereas in the case of a mixture of two HPAs, a mixed phase is formed as a result of the sintering of particles during re-sulfidation. The high concentration of mixed sulfides made it possible to provide a higher activity of catalysts in model reactions.Replacing alumina with mesostructured silica made it possible to increase the activity of unpromoted MoW catalysts. At the same time, similar values of the degree of sulfidation and dispersion, as well as the results of catalytic tests, seem to indicate that the formation of mixed MoWS2 phase does not occur on this type of supports, which requires additional research to be confirmed