Molybdenum -oxide MoO

An odd occurrence takes place when molybdenum oxide (MoO ) is heated... 

A particularly interesting aspect of electrochemistry is that it may allow transformations of bound substrates, by coupling proton(s) and electron(s) transfers. This makes possible to mimic certain steps of the reactions driven by metalloen-zymes. For example, the nitrosyl ligand in 7 (Sch. 6) is activated toward protic attack. Controlled potential reduction of 6 at the potential of the second process in the presence of PhOH (5-10 equiv) as a proton source consumed 6 F mol 6 and afforded the molybdenum oxide MoO(l,2-Ci, 11452)2] 8 and ammonia. The reductive cleavage of the N—O bond was proposed to involve a hydroxylamide intermediate, Sch. 7 [27]. Relevant to this is the fact that the chemical reduction of [Mo(NO)2(dttd)] by sodium borohy-dride or hydrazine in methanol produced [Mo(NO)(NH2O)(dttd)] with a side-on hy-droxylaminyl ligand [28]. 

Relatively good interface between Pt-MoOx could be established on that support with very low concentrations of the promoter NP, molybdenum oxide (MoO c) 2system prepared using 5% MoOx additive displayed reasonably high active Pt area and excellent oxygen reduction [96], Layered poly(3,4-ethylenedioxythiophene) in PEDOT/VS2 nanocomposite offers enhanced discharge capacity as a cathode material for rechargeable Li batteries. This activity is attributed to the electrochemical intercalation of Li into the PEDOT/VS2 nanocomposite [97],... 

The conversion of CO to CO2 can be conducted in two different ways. In the first, gases leaving the gas scmbber are heated to 260°C and passed over a cobalt—molybdenum catalyst. These catalysts typically contain 3—4% cobalt(II) oxide [1307-96-6] CoO 13—15% molybdenum oxide [1313-27-5] MoO and 76—80% alumina, JSifDy and are offered as 3-mm extmsions, SV about 1000 h . On these catalysts any COS and CS2 are converted to H2S. Operating temperatures are 260—450°C. The gases leaving this shift converter are then scmbbed with a solvent as in the desulfurization step. After the first removal of the acid gases, a second shift step reduces the CO content in the gas to 0.25—0.4%, on a dry gas basis. The catalyst for this step is usually Cu—Zn, which may be protected by a layer of ZnO. 

Chemical products are produced from technical-grade oxide in two very different ways. Molybdenum trioxide can be purified by a sublimation process because molybdenum trioxide has an appreciable vapor pressure above 650°C, a temperature at which most impurities have very low volatiUty. The alternative process uses wet chemical methods in which the molybdenum oxide is dissolved in ammonium hydroxide, leaving the gangue impurities behind. An ammonium molybdate is crystallized from the resulting solution. The ammonium molybdate can be used either directly or thermally decomposed to produce the pure oxide, MoO. ... 

In addition to these principal commercial uses of molybdenum catalysts, there is great research interest in molybdenum oxides, often supported on siHca, ie, MoO —Si02, as partial oxidation catalysts for such processes as methane-to-methanol or methane-to-formaldehyde (80). Both O2 and N2O have been used as oxidants, and photochemical activation of the MoO catalyst has been reported (81). The research is driven by the increased use of natural gas as a feedstock for Hquid fuels and chemicals (82). Various heteropolymolybdates (83), MoO.-containing ultrastable Y-zeoHtes (84), and certain mixed metal molybdates, eg, MnMoO Ee2(MoO)2, photoactivated CuMoO, and ZnMoO, have also been studied as partial oxidation catalysts for methane conversion to methanol or formaldehyde (80) and for the oxidation of C-4-hydrocarbons to maleic anhydride (85). Heteropolymolybdates have also been shown to effect ethylene (qv) conversion to acetaldehyde (qv) in a possible replacement for the Wacker process. 

Molybdau-kies, m. molybdenite, -ocker, m. molybdic ocher, molybdite. -oxyd, n. molybdenum oxide (specif., one higher than MojOa). -oxydul, n. molybdous oxide (MoO, also MojOa). 

Other procedures for a oxidation of ketones are based on prior generation of the enolate. The most useful oxidant in these procedures is a molybdenum compound, MoOs-pyridine-HMPA, which is prepared by dissolving M0O3 in hydrogen peroxide, followed by addition of HMPA. This reagent oxidizes the enolates of aldehydes, ketones, esters, and lactones to the corresponding a-hydroxy compound.189 190 191... 

The TPR and XRD measurements showed that molybdenum nitride is formed as y-Mo2N in the 12.5% and 97.1% MoO A C catalysts nitrided with NH3 at 973 K and 1173 K. For the catalysts nitrided at 773 K, there was no formation of molybdenum nitride on the surface, but adsorbed NH3 and NHX nitrided molybdenum oxides during TPD and TPR runs. 

It has been demonstrated that highly selective and active catalysts can be formed by activating either oxidized molybdenum carbide Mo2C or molybdenum oxide Mo03 itself with a hydrocarbon/hydrogen mixture. The active catalysts obtained from the two sources are similar in their catalytic behaviour and are probably both molybdenum oxycarbide (MoO Cy). They are selective for the isomerization of a number of n-hydrocarbons with the main products always consisting of monomethyl isomers but with an important contribution from the dibranched products,... 

These observations suggest a reaction scheme for bismuth molybdate catalysts where the allylic species is formed initially at a bismuth center and then reacts further at a molybdenum site to produce acrolein. Thus, once the allylic complex is formed, the MoO polyhedra are highly active and selective for acrolein formation. This hypothesis was tested by investigating the oxidation of bromoallyl (C3HjsBr) over molybdenum oxide 116). Since the C—Br bond in bromoallyl is much weaker than the C—H bond in propylene, the ease of formation of the allylic species should be significantly enhanced with bromoallyl compared with propylene. If the initial propylene activation occurs on bismuth, then the reaction of bromoallyl over molybdenum oxide should approach the activity and selectivity of propylene over bismuth molybdate. This was the observed result, and the authors concluded that the bismuth site was responsible for the formation of the allylic intermediate. 

Specific surface areas of the W03 and MoO, catalysts are shown in Table XI. It is noteworthy that the areas of both catalysts are large compared with those of the oxides without tungsten, and compared to molybdenum oxides, as was observed with the sulfate superacids, especially in the case of calcination at 800°C. 

Fig. 12. Schematic representation of the MoO octaedra in molybdenum oxide, a real position of the atoms b and c MoOfc octaedra d symbolic representation of comer sharing octaedra e edge-sharing octaedra.

In addition to conventional static and MAS measurements on molybdenum oxide catalysts, static-echo techniques have also been applied [125, 127, 129]. Spin-echo spikelet experiments allow the presence of dynamically active surface-interactive molybdenum oxide species to be resolved. Figure 5.20 compares the spikelet-echo spectra of MoO, /Al203 of different loadings before and after calcination. The existence of the broad resonance on which the observed spikelets are superimposed indicates that the surface is dynamically inhomogeneous. As discussed in Section 5.2.22 the basis of the spikelet-echo experiment is that surface species with high mobility will have short spin-spin relaxation times in comparison with species immobilized on the surface. The spikelet-echo experiment is designed to distinguish species on the basis of their T2 values. 

The electrochemical reversibility of the M(VI)/M(V) couple for the complexes with sterically hindered ligands contrasts with the reported behavior of the [MoO(SPh)4] complex, which exhibited electrochemical irreversibility for the Mo(V)/Mo(VI) step but a reversible Mo(IV)/ Mo(V) couple. The sterically hindered aromatic substituent groups stabilize the molybdenum(VI) complex and decrease relative to the thiophenol derivative. The molybdenum(VI) species can also be isolated by chemical oxidation. [MoO(PFTP)4] was prepared by chemical redu-tion of [MoO(PFTP)4] . The presence of the electron-withdrawing substituents on the aromatic thiolate increases E ei relative to the thio-phenolate derivative. Evidently the properties of these last complexes are influenced primarily by the electron-withdrawing characteristics of the fluorine substituents rather than by steric factors (33). 

Finally, molybdenum oxide clusters have been prepared as neutral and ionic species in gas phase and studied by quantum chemical methods at various levels of theory. This includes MoO [195-198], MoO , n=l-3 [199], M0O3, Mo04, M0O4H2, Mo205, and M02O6, [200] where the calculations provide a satisfactory description of structural, energetic, and spectroscopic properties. 

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