Vanadium oxide hardness

Akimoto et al 6 conclude from e.s.r. spectra that different forms ofV4+ ions are formed depending on the support. A reactive form, which is also preferentially formed in V205 is necessary for high selectivity in benzene oxidation. In well spread vanadium oxide on Al2 03 and MgO this is hardly formed in contrast to Si02 on which the dispersion is much less. 

Fig. 7. Diagrams of the relaxed IDM (Part a) and the relaxed AIM FF indices (Part b) of toluene in the surface complex M with the bipyramidal cluster of the vanadium oxide surface. The modes are arranged in accordance with increasing hardnesses h the hardness tensor reflects the isolated reactant AIM charges from the MNDO and scaled-INDO calculations on toluene and cluster, respectively. Numbers in parentheses report the w values. The three diagrams in Part b display the AIM FF distribution of toluene in M, calculated from the toluene block of i/ 1, and its resolution into the CT and P components, respectively...

The deactivation of the catalyst observed in Stage II is probably caused by the sintering of the vanadium oxide layer. The results of our previous work [13] show that reoxidation of Pd 0) is only possible with highly dispersed vanadium oxide. Catalysts on bulk vanadium pentaoxide show rapid deactivation due to the fact that reoxidation of Pd(0) hardly proceeds. Also catalysts supported on silica show rapid deactivation, as a result of the low dispersion of vanadium oxide on silica. 

Fig. 10. Schematic contours of the four energetically most important (highest w,) normal population modes in the model 4-pyramids cluster of the vanadium oxide catalyst see caption to Fig. la for the contour interpretation. The V( -h 1) ion is in the centre of each square pyramid unit, surrounded by the neutral oxygen atoms. The mode number a indicates its position in the set ordered in accordance with increasing mode hardness...

The reaction is carried out in the vapour phase by passing a mixture of naphthalene and air over a catalyst such as molybdenum or vanadium oxides at about 500°C. The exit gases are cooled and the phthalic anhydride is collected and purified by distillation under reduced pressure. Phthalic anhydride is a white crystalline solid, m.p. 131°C. Phthalic anhydride gives polyesters which are compatible with styrene and the cross-linked products are hard and rigid. 

Vanadium is an excellent alloy metal with iron that produces hard, strong, corrosion-resistant steel that resists most acids and alkali. It is even more resistant to seawater corrosion than is stainless steel. Vanadium is difficult to prepare in a pure form in large amounts. Impure forms seem to work as well as a very pure form of the metal when used as an alloy. When worked as a metal, it must be heated in an inert atmosphere because it will readily oxidize. 

Vanadyl Phosphate Catalysts. — For the oxidation of C4-hydrocarbons to maleic anhydride, vanadyl phosphate catalysts with a variety of V P ratios and different additives have been proposed. Nakamura etal.123 observed for V P = 1 2, an average oxidation number of four for vanadium, highly aggregated vanadium ions and a high selectivity. Varma and Saraf124 also studied this reaction and on the basis of kinetic results propose a two-stage redox mechanism. They also concluded that maleic anhydride is hardly oxidized to carbon oxides, which are mainly formed in a side reaction from the original... 

Very hard carbides result from strongly heating the oxides with carbon. They are empirically MC and have the NaCl structure. Vanadium also forms V4C3 which has a defect structure, carbon atoms being missing from some of the lattice positions. 

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