Vanadium nitrogen system

In the vanadium-nitrogen system, the phases /3-V2N and 5-VNi x have cph and fee struetures, respeetively. Carlsson et have reviewed the V-N system and reinvestigated the vanadium-rieh portion. Compiled data and results of a phase diagram study based on diffusion eouples have been used to eonstruet the phase diagram shown in Figure 7. 

A large amount of work has been carried out, primarily by Shilov, on the chemical fixation of dinitrogen using various vanadium-containing systems. However, no stable dinitrogen complexes of vanadium have been reported or in situ nitrogen fixation observed with phosphines present. 

A number of nitrogen-fixing bacteria contain vanadium and it has been shown that in one of these, Azotobacter, there are three distinct nitrogenase systems based in turn on Mo, V and Fe, each of which has an underlying functional and structural similarity.This discovery has prompted a search for models and the brown compound [Na(thf)]+[V(N2)2(dppe)2] (dppe = Pli2PCH2CH2PPh2) has recently been prepared by reduction of VCI3 by sodium naphthalenide... 

Loop Tests Loop test installations vary widely in size and complexity, but they may be divided into two major categories (c) thermal-convection loops and (b) forced-convection loops. In both types, the liquid medium flows through a continuous loop or harp mounted vertically, one leg being heated whilst the other is cooled to maintain a constant temperature across the system. In the former type, flow is induced by thermal convection, and the flow rate is dependent on the relative heights of the heated and cooled sections, on the temperature gradient and on the physical properties of the liquid. The principle of the thermal convective loop is illustrated in Fig. 19.26. This method was used by De Van and Sessions to study mass transfer of niobium-based alloys in flowing lithium, and by De Van and Jansen to determine the transport rates of nitrogen and carbon between vanadium alloys and stainless steels in liquid sodium. 

Development of systems using vanadium(II) that fix nitrogen in an aqueous environment34... 

Nitriloacetic acid reacts with vanadium-(m). -(iv), or -(v) oxides to form oxovanadatranetrionic acid (38). The crystal structure of [VO(CjQHgNO)2] (CjgHgNOH = 2-methyl-8-quinolinol) has shown that the vanadium atom has a five-co-ordinate trigonal-bipyramidal environment, with three oxygen atoms in the equatorial plane and the two nitrogen atoms of the bidentate ligand in the apical positions. The optimum conditions for the formation of a 1 2 2 vanadium(iv)-morin-4-aminoantipyrine system have been described as pH 5, a tenfold excess of morin (39), and a 3300-fold excess of 4-amino-antipyrine. ... 

Selective Catalytic Reduction (SCR) process is very similar to SNCR with the exception that a catalyst is used to accelerate the reactions at lower temperatures allowing it to be applied to both full and partial-burn regenerators. An SCR system consists of a catalyst bed installed in the flue gas line of a combustion system. Ammonia is injected into the flue gas with air in the presence of a catalyst. The catalyst is typically oxide forms of vanadium and tungsten. The ammonia selectively reacts with NOx to form molecular nitrogen and water via an exothermic reaction that has achieved > 90% reduction in NO when applied to an FCCU. 

The isolation of a vanadium nitrogenase suggests that vanadium may have a more important role in the nitrogen cycle than was recognized. This vanadium enzyme may have similarities with the chemical systems described in Section 33.3.8.1. 

Vanadium (II)/catechol systems can be useful in fixation of atmospheric nitrogen, reducing it to ammonia [244-246]. A detailed EPR study concluded that the active catalyst is a trinuclear V-Cat species 966 [125a,246,247] ... 

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