Carbon monoxide niobium

The carbothermic reduction processes outlined so far apply to relatively unstable oxides of those metals which do not react with the carbon used as the reductant to form stable carbides. There are several metal oxides which are intermediate in stability. These oxides are less stable than carbon monoxide at temperatures above 1000 °C, but the metals form stable carbides. Examples are metals such as vanadium, chromium, niobium, and tantalum. Carbothermic reduction becomes complicated in such cases and was not preferred as a method of metal production earlier. However, the scenario changed when vacuum began to be used along with high temperatures for metal reduction. Carbothermic reduction under pyrovacuum conditions (high temperature and vacuum) emerged as a very useful commercial process for the production of the refractory metals, as for example, niobium and tantalum, and to a very limited extent, of vanadium. 

For a reduction pressure of 10 4 atm, NbO and Nb2C react to form niobium and carbon monoxide at 1687 °C. When the carbon monoxide pressure is kept at 10-6 atm, the reaction resulting in the formation of the metal would occur, according to the diagram, at 1382 °C. 

V metals, vanadium has the least tendency to deoxidize by carbon monoxide evolution. This means that, at a given temperature and a given value of Pco, the residual carbon and/or oxygen contents in vanadium will be compared more to niobium and tantalum. In other words, the removal of carbon and/or oxygen from vanadium will occur to a much lesser extent than in the cases of niobium or tantalum. The effect of carbon deoxidation can be quite complicated if there is a significant loss of the metal by vaporization. The requirement of a low vapor pressure is also better satisfied by niobium and tantalum than by vanadium. 

In the case of vanadium, the suboxide, vanadium monoxide, would be more volatile than carbon monoxide except at very high carbon concentrations in the metal. The removal of the residual oxygen from this metal by carbon deoxidation is, therefore, difficult. In the case of niobium and tantalum, the partial pressure of carbon monoxide is higher than that of niobium monoxide or tantalum monoxide, even when the residual carbon concentration in the metal is as low as 200 ppm. It may therefore be expected that practically all the oxygen would be removed by evaporation of carbon monoxide without any metal loss from niobium and tantalum metals containing both oxygen and carbon. 

Insertions of isocyanide into niobium-carbon bonds follow a path similar to that with vanadium, resulting in the formation of the 7]2-iminoacyl complexes, which can then be involved in further chemistry.175 176 The reaction of acetone with cyclopentadienyl complex 110 under a carbon monoxide atmosphere gives the if -acetone compound 111. Complex 111 subsequently undergoes either stepwise insertion of two isocyanides via 112 or double insertion of the isocyanide to give complex 113 (Scheme 48).177... 

In a similar manner, UV irradiation of (triphenylsilyl)phenylacetylene with cyclopentadienylmanganese tricarbonyl 121) and cyclopentadienyl-niobium tetracarbonyl 122) results in elimination of carbon monoxide and formation of monodentate acetylene complexes (R = Ph) ... 

The action of carbon tetrachloride or a mixture of chlorine with a hydrocarbon or carbon monoxide on the oxide.—H. N. Warren 9 obtained aluminium chloride by heating the oxide to redness with a mixture of petroleum vapour and hydrogen chloride or chlorine, naphthalene chloride or carbon tetrachloride was also used. The bromide was prepared in a similar manner. E. Demarpay used the vapour of carbon tetrachloride, the chlorides of chromium, titanium, niobium, tantalum, zirconium, cobalt, nickel, tungsten, and molybdenum H. Quantin, a mixture of carbon monoxide and chlorine and W. Heap and E. Newbery, carbonyl chloride. 

In this paper we review the results of our systematic work on the catalytic and adsorptive properties of transition metal carbides (titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, and iron). We focus our attention on the oxidation of hydrogen, carbon monoxide, ammonia, and the oxidative coupling of methane. The first two reactions are examples of complete (non-selective) oxidation, while the oxidation of ammonia simulates a selective oxidation process. The reaction of oxidative coupling of methane is being intensively explored at present as a means to produce higher hydrocarbons.5 10... 

Oxidizer, Poison, Corrosive SAFETY PROFILE Poisonous and corrosive. Very reactive, a powerful oxidizer. Explosive or violent reaction with organic materials, water, acetone, ammonium halides, antimony, antimony trichloride oxide, arsenic, benzene, boron, bromine, carbon, carbon monoxide, carbon tetrachloride, carbon tetraiodide, chloromethane, cobalt, ether, halogens, iodine, powdered molybdenum, niobium, 2-pentanone, phosphoms, potassium hexachloroplatinate, pyridine, silicon, silicone grease, sulfur, tantalum, tin dichloride, titanium, toluene, vanadium, uranium, uranium hexafluoride. 

We found also that (77-C5H,)V(CO)3PPh3 as well as its niobium analog, when irradiated, underwent substitution of one PPh3 and one CO by tolan. Hence, niobium (and tantalum) complexes of the type are able to attach a third molecule of tolan and transform this to hexaphenylbenzene, unlike the vanadium analog, which transforms just two tolans to tetraphenyl-cyclobutadiene or, if irradiated, combines them with carbon monoxide and produces tetraphenylcyclone. 

Some metal oxide catalysts are activated by thermal reduction with hydrogen or carbon monoxide. For example, the catalytic activity of molybdenum oxide and tungsten oxide for the metathesis reaction of olefins is very much enhanced by their slight reduction (1). The catalytic activity for butene isomerization and ethene oligomerization appears on niobium oxide by its... 

Fig.5 shows the dependence of the catalytic activity of Nb20s/PVG photoactivated in the presence of ethene on the niobium content in the catalyst. The activity increases monotonously with increase in the Nb content. On the other hand, Anpo et al-have shown that tetrahedrally coordinated Mo or V ion with double-bonded oxygen ions(see Reactions[1] and [2]), which take part in photochemical process of their oxides, is predominantly formed at a rather low content in porous Vycor glass (16,17). Furthermore, it has been found that photocatalyzed metathesis (13) and photooxidation of carbon monoxide observed for Nb205/PVG show a maximum activity at 1 mg g-PyG" of the Nb content. This difference in the dependence of the activities on the Nb content... 

OC, Carbon monoxide (Continued) cobalt, iron, osmium, and ruthenium complexes, 21 58-65 iron complex, 21 66, 68 manganese complexes, 23 34 molybdenum complexes, 23 4-9 niobium complexes, 23 34 palladium complex, 21 49 rhodium complexes, 23 124 ruthenium complex, 21 30 OCH4, Methanol, iridium complexes, 23 127 rhodium complexes, 23 127, 129 OCjHs, Acetone, compd. with carbonyltri-p.-chloro-chlorotctrakis-(triphenylphosphine)diruthcnium (1 2), 21 30... 

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