Organic Solvent-Free Olefins and Alcohols (ep)oxidation Using Recoverable Catalysts Based on [PM12O40]3- (M = Mo or W) Ionically Grafted on Amino Functionalized Silica Nanobeads

Evaluation of Phosphopolyoxometalates with Mixed Addenda (Mo, W, V) as Corrosion Inhibitors for Steels

Nowadays, choosing a corrosion inhibitor is not only based on efficiency, but must also consider the toxicity of the compound, the impact on the environment, and, obviously, the regulations in the field. In the last two decades, a special class of substances has begun to be studied, namely polyoxometalates (POMs). Their electronic properties and redox characteristics make the polyoxometalates potential candidates to be used in many electrochemical processes, and as potential corrosion inhibitors. Electrochemical methods such as a Tafel extrapolation plot, chronopotentiometry, or gravimetry have been used to establish the capacity of corrosion inhibition of S235 and SS304 steels in the presence of phosphovanadomolibdate acid (@PMoV) and phosphovanadotungstate acid (@PWV) in 0.5 M sulphuric acid solution. The inhibition efficiency for S235 steel is about 90.6% for @PMoV, and 69.5% for @PWV after 24 h of immersion. In the case of SS304 steel, polyoxometalates have similar effects: the inhibition degree, as a function of Flade potential, is 4.66 for @PMoV; better than 3.26 for @PWV, with both proving the passivant effect.

Molybdenum, Vanadium, and Tungsten-Based Catalysts for Sustainable (ep)Oxidation

This article gives an overview of the research activity of the LAC2 team at LCC developed at Castres in the field of sustainable chemistry with an emphasis on the collaboration with a research team from the University of Zagreb, Faculty of Science, Croatia. The work is situated within the context of sustainable chemistry for the development of catalytic processes. Those processes imply molecular complexes containing oxido-molybdenum, -vanadium, -tungsten or simple polyoxometalates (POMs) as catalysts for organic solvent-free epoxidation. The studies considered first the influence of the nature of complexes (and related ligands) on the reactivity (assessing mechanisms through DFT calculations) with model substrates. From those model processes, the work has been enlarged to the valorization of biomass resources. A part concerns the activity on vanadium chemistry and the final part concerns the use of POMs as catalysts, from molecular to grafted catalysts, (ep)oxidizing substrates from fossil and biomass resources.

Molybdenum-, Vanadium-, and Tungsten-Containing Materials for Catalytic Applications

As chemists, we are still fascinated by the magic of nature [...]

Green solvent free epoxidation of olefins by a heterogenised hydrazone-dioxidotungsten(vi) coordination compound

A new mononuclear tungsten coordination compound, [WO₂L(CH₃OH)] (1), was synthesized by the reaction of WCl₆ and H₂L (H₂L = (E)-4-amino-N′-(5-bromo-2-hydroxybenzylidene)benzohydrazide) in methanol. Both the H₂L and compound 1 were characterized by elemental analysis and UV-Vis, FT-IR and NMR spectroscopic methods. The molecular structure of compound 1 was also determined by single crystal X-ray analysis which confirmed the compound is a mononuclear coordination compound of cis-dioxidotungsten(vi) containing a free amine functionality on the ligand. Compound 1 was supported on propionyl chloride-functionalized silica gel by amidification reaction to obtain a heterogeneous catalyst. The obtained heterogeneous catalyst was characterized by FT-IR spectroscopy, thermal gravimetric analysis (TGA), diffuse-reflectance spectroscopy (DRS), X-ray diffraction analysis (XRD), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) and its catalytic activity was investigated in the epoxidation of olefins with hydrogen peroxide under solvent free conditions. The catalyst was successfully recovered several times and the recovered catalyst was also characterized by various methods including FT-IR, DRS, TGA, SEM and EDX analyses. The results indicated this heterogeneous catalytic system is an effective and selective catalyst for epoxidation of olefins and can be reused several times without significant change in its catalytic activity.

In this study the solvent free catalytic oxidation of olefins by a new silica supported hydrazone-dioxidotungsten(vi) coordination compound is investigated.

Replacement of Volatile Acetic Acid by Solid SiO2@COOH Silica (Nano)Beads for (Ep)Oxidation Using Mn and Fe Complexes Containing BPMEN Ligand

Mn and Fe BPMEN complexes showed excellent reactivity in catalytic oxidation with an excess of co-reagent (CH3COOH). In the straight line of a cleaner catalytic system, volatile acetic acid was replaced by SiO2 (nano)particles with two different sizes to which pending carboxylic functions were added (SiO2@COOH). The SiO2@COOH beads were obtained by the functionalization of SiO2 with pending nitrile functions (SiO2@CN) followed by CN hydrolysis. All complexes and silica beads were characterized by NMR, infrared, DLS, TEM, X-ray diffraction. The replacement of CH3COOH by SiO2@COOH (100 times less on molar ratio) has been evaluated for (ep)oxidation on several substrates (cyclooctene, cyclohexene, cyclohexanol) and discussed in terms of activity and green metrics.

Pseudohomogeneous metallic catalyst based on tungstate-decorated amphiphilic carbon quantum dots for selective oxidative scission of alkenes to aldehyde

Herein, we present an interesting role of tungstate-decorated amphiphilic carbon quantum dots (A-CQDs/W) in the selective oxidative cleavage of alkenes to aldehydes. In this work, for the first time, we disclose an unprecedented tungstate-based oxidative system incorporating A-CQDs as a bridge to the homogeneous catalyst for selective and efficient cleavage of a wide substrate scope of alkenes into aldehydes. The A-CQDs/W were synthesized via a one-step hydrothermal synthesis approach using 1-aminopropyl-3-methyl-imidazolium chloride and stearic acid for the surface modification, following by anion-exchange to immobilize WO₄^-2 to A-CQDs. The A-CQDs/W act as a pseudohomogeneous metallic catalyst (PMC) for selective oxidative scission of alkenes under phase transfer catalysts (PTC) free condition without over oxidation to acids, using water and H₂O₂ as a green oxidant. Thanks to the sub-nanometric size and novel engineered chemical structure, this PMC and reactants are in the same phase, besides they can be easily isolated from each other by extraction processes. The synthesized PMC exhibited excellent solubility and stability in various solvents. Interestingly, the system's high conversion efficiency was preserved even after eight catalytic cycles indicating the recyclability of the synthesized PMC. We believe that this study provides a significant and conceptually novel advance in oxidative cleavage chemistry.