Molybdenum oxide cation

The cations in transition metal oxides often occur in more than one oxidation state. Molybdenum oxide is a good example, as the Mo cation may be in the 6-r, 5-r, and 4+ oxidation states. Oxide surfaces with the cation in the lower oxidation state are usually more reactive than those in the highest oxidation state. Such ions can engage in reactions that involve changes in valence state. 

XRD patterns of the prepared samples V-Mo-Zeolite are similar to that of zeolites which suggests that the metal species (i.e. oxide, cations,...) are well dispersed through the zeolites structure and the absence of bulk phases in the XRD patterns implies that for these samples the molybdenum and vanadium oxides are present in either a nanocrystalline state or as a small crystallites which measured less than 4 nm in diameter. Furthermore, XRD and FTIR (1500-400 cm 1) showed no significant damage of the zeolite host structure after exchange and thermal treatment except for the sample V2MoMor. 

Allows a better dispersion of molybdenum trioxide from the external surface of the mesoporous support into its internal nanochannels. The active sites (possibly pairs of neighboring molybdenum cations) thus increases. As the result of better dispersion, the reduced molybdenum oxide species formed during the course of reaction through its entire surfaces and thus lowers the possibility of sintering in a reduced environment. Here, we see that the deactivation rate is the highest in Mo/Si02 catalyst due to the lowest surface area. 

To what extent can the example of a solid exoskeleton be replicated in the laboratory Going against most contemporary examples of flexible artificial cells, Muller and Rehder published an example of a complex molybdenum oxide that spontaneously forms discrete nanospheres [23], The hollow spheres were porous and allowed lithium cations to pass through the exoskeleton. While this a perhaps an extreme example of what may be considered an artificial cell, the authors assert that the presence of ion selective channels through the encapsulating oxide is directly analogous to natural ion channels in organic cells. 

Stein et al. and Janauer et al. have synthesized layered mesostructured materials of (C,9H42N)6(H2W,204o) and [Ci2H25N(CH3)3]6(H2Wi2O40), respectively [2,8]. These materials are of great interest because their walls are made of cluster anions, in contrast to the amorphous walls of the other materials. The tungsten, vanadium, niobium, and molybdenum oxide precursors reacting with cationic surfactants, often form similar cluster ion salts with lamellar structures [2]. 

CS planes across which the MoOe octahedra share edges rather than comers. These extended defects exist even at modest temperature due to the large mobility of oxygen vacancies, Further, the defects are stabilized by relaxation as a result of Mo cation displacement from their centers of symmetry to interstices. Homologous series of molybdenum oxides [1, 3, 12, 34, 154, 158, 160, 163, 164], which are based on CS plane formation starting from a ReOs-type structure, include MOn03n-i and Mon03 .2 systems. 

P.J. Zapf, R.C. Haushalter, and J. Zubieta. Crystal engineering of inorganic/organic composite solids the structure-directing role of aromatic ammonium cations in the synthesis of the step -layered molybdenum oxide phase [4,4 -H2bpy][Mo7022] H20, Chem. Commun., 321 (1997)... 

Pretreatment involving the partial reduction of the oxide with hydrogen can similarly produce significant effects that vary with the metal oxide used. The effect that prereduction has on supported chromia and molybdenum oxides is widely different. On a chromia catalyst, the reduction step leads to the formation of Br0nsted sites, which then catalyze the isomerization reaction via a cationic intermediate. On a reduced molybdena catalyst, metathesis-type mechanisms dominate, with the cationic mechanism proceeding only on a fully oxidized molybdena surface. 

The iron-mediated synthesis of 2-oxygenated carbazoles is limited. On the other hand, a molybdenum-mediated approach works as a complementary route (Scheme 23.24) [31]. Similar to iron-coordinated cation 55, molybdenum-coordinated cations 61 react with electron-rich anilines 62 to give (if-cyclohexenyl)molybdenum complex 63. Then the oxidative cyclization of 63 followed by the subsequent aromatiza-tion and demetallation using activated manganese dioxide afforded the corresponding... 

Fig. 8. Redox behavior of tungsten and molybdenum oxide clusters in zeolite Na-Y, after [239,246]. Na+ cations...

In 1826 J. J. Berzelius found that acidification of solutions containing both molybdate and phosphate produced a yellow crystalline precipitate. This was the first example of a heteropolyanion and it actually contains the phos-phomolybdate ion, [PMoi204o] , which can be used in the quantitative estimation of phosphate. Since its discovery a host of other heteropolyanions have been prepared, mostly with molybdenum and tungsten but with more than 50 different heteroatoms, which include many non-metals and most transition metals — often in more than one oxidation state. Unless the heteroatom contributes to the colour, the heteropoly-molybdates and -tungstates are generally of varying shades of yellow. The free acids and the salts of small cations are extremely soluble in water but the salts of large cations such as Cs, Ba" and Pb" are usually insoluble. The solid salts are noticeably more stable thermally than are the salts of isopolyanions. Heteropoly compounds have been applied extensively as catalysts in the petrochemicals industry, as precipitants for numerous dyes with which they form lakes and, in the case of the Mo compounds, as flame retardants. 

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