Molybdenum species formation

A reaction that has not apparently been attempted with the analogous uranium and molybdenum species is that43 between polyfluoro aromatics and XeF+WF2, e.g. formation of 7, 8 and 9. 

These Mo-based cyanide and insulin systems are suggested to operate similarly to the molybdothiol systems, via the formation of a coordinatively unsaturated oxo-molybdenum species as catalyst, which binds N2 side-on and reduces it by two electrons to N2H2 (see Equations 23, 24, 25). The intermediacy of N2H2 in the formation of NH3 is supported by the reduction of fumarate to succinate by these systems when operating under N2. Succinate is not produced when other substrates, for example, acetylene, are being reduced. 

As shown in Figure 9, UV-irradiation of Mo-MCM-41 in the presence of a mixture of NO and CO leads to the formation of N2 and C02 with a linear dependence on UV-irradiation time, whereas the turnover frequency exceeds 1.0 after 2h (Tsumura et al., 2000). After 3h, NO conversion and selectivity towards N2 are close to 100%, with only a small amount of N20 formed. Figure 10 shows that there is a good correspondence between the yield of N2 produced and the yield of PL of tetrahedral molybdenum species and the amount of Mo4+ ions generated upon... 

The measurements of NO acscrption capacity, related to the dispersion of Mo and Mi-Mo sulfides, indicate curtain differences between the freshly sulfided and spent catalysts (e.g.after 3 days in the WCS). The drop of adsorption capacity was especially visible for nickel containing samples or hydrogen forms of Y-zeolites used as supports (ref.5). These observations led us to the conclusion that at least two factors can be responsible for the decrease of activity certain rearrangement of the sulfided molybdenum species in the presence of support hydroxyl groups or formation of carbonaceous deposits over Mo sulfides. Coke formation can prevent access of NO to adsorption sites-... 

Adsorption can result either from electrostatic interactions between molybdates and boehmite surface or from chemical interactions, i.e. from the formation of a iono-covalent bond through a chemisorption mechanism. The interaction mode is governed by the boehmite hydroxyl surface groups as well as by the solution molybdate species. The determination of the nature and concentration of the molybdenum species involved in the experiments (before and after the adsorption equilibrium) has been carried out by computer simulations (cf 2.2). Concerning hydroxyl surface groups, we referred to MUSIC modeling [11,12] as well as to the work of Raybaud et al. [13], who performed DFT studies on boehmite and so determined boehmite morphological and structural surface properties. 

Acetic acid formed via isopropanol and acetone could involve Mo " species. With the second way, acrolein and acrylic acid are obtained with the participation of Mo species. When the temperature increases the first way of the scheme is favored owing to a surface restructuration of the oxide Mo 03 which can contain pentacoordinated molybdenum species. The addition of bismuth to these phases decreases slightly the activity, the formation of acetic acid being supressed. When water is added to the reagent stream, the activity does not change, but the desorption of oxygenated compounds is favored and the selectivity towards acids enhanced. 

In recent years, a lot of research effort has been directed towards dehydroaromatisation of methane in which methane is converted to aromatic products such as benzene and naphthalene in addition to hydrogen. Perhaps the most well studied system has been that employing Mo/ZSM-5 based catalysts, where the bifunctional interaction between the zeolite Bronsted acidity and molybdenum species is well recognised. Under reaction conditions, the active molybdenum species are known to be in the form of carbides or oxycarbides, and recently it has been proposed that the a-MoCi-x phase is the most active form. Deactivation, primarily due to coke formation, is well precedented in this reaction and represents a major obstacle to be overcome in the successful application of these catalysts. In this respect, it is interesting to note that Ichikawa and co-workers have published studies indicating that the inclusion of low levels of CO or CO2 in the feed can promote the reaction via the suppression of coke formation in the case of both Mo/HZSM-5 and Re/HZSM-5 catalysts. Other approaches adopted towards this aim have been the inclusion of second metal components and a reduction of the acid strength of the HZSM-5 support. ... 

Recent papers describe models for molybdenum-containing enzymes [106], Certain vanadium complexes have been described to mimic the binding site reactions of vanadium haloperoxidases [62, 107], Scheme XI.20 demonstrates the mechanism of active species formation in bromoperoxidase proposed on the basis of the investigation of model reactions [108],... 

In the anaerobic digester environment, one would thus expect sulfide reactions to dominate the Mo chemistry since the oxy-anions of the more reduced forms of this metal are relatively unstable (Tucker et al, 1997). For Facility J, total dissolved Mo concentration in the anaerobic digester supernatant was high (47 /rg/l Fig. 3) but the Mo(VI)/(total dissolved Mo) ratio was only 0.15, showing substantive formation of soluble species other than molybdate in the system. The dominant form of molybdenum present in the digester supernatant is unknown and is believed to be molybdenum sulfides. Formation of thio-complexes is also suggested by the ratio... 

The best catalysts were supported on supports composed of 40 wt% of TiOa and 60 wt% Zr02 and containing 8 wt% of Mo and 3 wt% of Ni. They explained that the better activity of 40 wt% of Ti02 and 60 wt% Zr02 catalyst is due to appropriate ratio of surface acid-base properties of the support. Their characterization measurements suggest that introduction of nickel ions onto the molybdenum catalysts causes the increase of dispersion of sulphided molybdenum species independently from support composition. The presence of Ni " on the surface of molybdenum catalysts decreases the temperature of reduction of Mo ions and therefore facilitates the formation of M0S2 and Ni-Mo-S species at lower temperature with better dispersion. 

PdPh(SEt2)(/t-02CMe)2 2Pd. In related reactions, formation of alcohols and ethers in the presence of MoO(02>2 HMPT H2O is proposed to occur via cyclopalladation, oxidation by Mo(VD, and C—O bond formation involving an oxygen atom of the molybdenum species or methoxide from the methanol solvent. ... 

A further application of TLRC in the biochemical field is in the assessment of the activity of enzymes, where TLRC can be used to monitor and quantitate the products during the course of an enzyme reaction such as deiodination. Other examples of the use of TLRC in biochemical studies are the qualitative assessment of the complex-forming ability of metals and ligands in biological systems and the complex formation of heavy metal chelates, such as molybdenum species with poly-aminocarboxylic acids. 

Another type of demasking involves formation of new complexes or other compounds that are more stable than the masked species. For example, boric acid is used to demask fluoride complexes of tin(IV) and molybdenum(VI). Formaldehyde is often used to remove the masking action of cyanide ions by converting the masking agent to a nonreacting species through the reaction ... 

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