Average valence state

Hall et al. (63) found that the active species in the hydrogenolysis of cyclopropane are Mo(IV) in reduced M0O3-AI2O3 catalysts. Also, Burwell and Bowman found that the hydrogenolysis of cyclopropane at 100 C (64) and also propane at 300°C (65) occurs over Mo(IV), Mo(II), and Mo(0) catalysts, which were prepared from Mo(CO)g on AI2O3. The average valence state... 

Module type and average valence state of the lanthanide higher oxides... 

It should be noted in this connection that, for ethylene polymerisation in the presence of a non-supported catalyst such as TiCl4-AlR3 (R = Et, z -Bu), polymerisation proceeds at the maximum rate when the average valence state of titanium is 2 [304], However, while catalysts with divalent titanium compounds as precursors are known to be highly active for the polymerisation of ethylene, their activities for the polymerisation of a-olefins are generally low [51,240],... 

The nature of the catalyst sites was given particular attention. Reduction of the catalyst, from the amount of carbon dioxide produced, indicated an average valence state of the chromium of 4.5 0.2 comparable to that observed in reduction by ethylene. The conclusion was that the active sites contained chromium in a valence state above Cr — possibly Cr. However, in view of a relationship between polymerization activity and Cr concentration [161] for extensively reduced catalysts, other catalytic species may exist. 

The catalyst precursor VOHPO4 0.5 H2O was prepared from aqueous solution as described in [5] but without the addition of H2SO4. It was calcined in N2 (fresh catalyst) and conditioned in a butane(1.5 %)- air mixture [5] to obtain a (VO)2P20 catalyst which showed the characteristics of an equilibrated catalyst described by Ebner and Thompson [11]. The average valence state of vanadium amounted to 4.02, the P V ratio was 1.0 and the specific surface area was about 10 m /g. It is assumed that ions formed in the conditioning procedure of the... 

The preparation of mixed oxide compositions of vanadium and phosphorus and the use of these as catalysts for the oxidation of hydrocarbons such as n-butane to maleic anhydride is known in the art. In U.S. Pat. No. 4,111,963 the importance of reducing the vanadium used in a vanadium/phosphorus oxide (V/P/O) catalyst to the four oxidation state is described. Preferred is the use of concentrated hydrochloric acid as the reaction medium to bring about this reduction and preferred catalysts have a phosphorus to vanadium atom ratio of 1 2 to 2 1 and a porosity of at least 35%. In U.S. Pat. No. 3,864,280 the reduction of the vanadium in such a catalyst system to an average valence state of 3.9-4.6 is emphasized the atomic ratio of phosphorus to vanadium is 0.9-1.8 1. Isobutyl alcohol is used as a solvent for the catalyst preparation, with the indication that an increase in catalyst smface area, over that obtained from use of an aqueous system, is achieved. The addition of promoters to the V/P/O catalyst compositions used for the oxidation of hydrocarbons to maleic anhydride is also disclosed in the art. Thus, in U.S. Pat. Nos. 4,062,873 and 4,064,070 are disclosed vanadium/phosphorus/silicon oxide catalyst compositions made in an organic medimn. In U.S. Pat. Nos. 4,132,670 and 4,187,235 are disclosed processes... 

In various competing reaction networks proposed for the butane oxidation [6, 7], furan is an intermediate. The extent to which it is formed has been linked to the oxidation state of the VPO. Rodemerck et al. prepared VPO catalysts exhibiting six different oxidation states ranging from 3.18 to 4.90 [8]. These are the average valence states as determined by potentio-metric titration. The catalytic behavior of the respective samples as determined wift a TAP reactor setup is summarized in Table 1. 

The redox potential of the irradiated fuel material is influenced by the buildup of the fission products. In their review paper, which is strongly influenced by thermodynamic considerations, Assmann and Stehle (1984) stated that the average valency state of the generated fission products is slightly less than the valency state of uranium or plutonium, as a consequence of which the oxygen partial pressure in... 

With the variation of average valence state caused by the variation of the concentration of localized electrons, the ionic radii vary and with the variation of the concentrations of vacancies or interstitial cation formation, the binding energy of the crystal may vary. These variations result in the variation of the lattice constants of the crystal. The binding energy and the lattice constants are closely related to the mechanical properties. Then, with the nonstoichiometric compositional variation, the mechanical properties of the oxide may vary. The relationship of materials properties and nonstoichiometry is schematically shown in Fig. 3. In the near future, nonstoichiometry and defect chemistry become very important base... 

S. lijima, R. Saida, I. Motoyama, H. Sano, The temperature dependence of the trapped and averaged-valence state in mono-oxidized dialkylbiferrocenes. Bull. Chem. Soc. Jpn. 54, 1375-1379 (1981)... 

Figures 2.2 and 2.3 provide additional information on the oxidation state of titanium at various Al/Ti ratios and the ethylene polymerization rate vs the average valence state of titanium, respectively.

Figure 2.2 Dependence of average valence state of titanium on catalyst composition catalysts prepared from TiCl and triethylaluminum at 80oC in cyclohexane. Reprinted from [11] with permission from American Chemical Society.

Figure 2.3 Dependence of catalytic activity on average valence state of titanium. Catalysts prepared from TiCl and triethylaluminum or triisobutylaluminum. Reprinted with permission from [11] American Chemical Society.

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