Transition group oxides

Hydrogenation and dehydrogenation employ catalysts that form unstable surface hydrides. Transition-group and bordering metals such as Ni, Fe, Co, and Pt are suitable, as well as transition group oxides or sulfides. This class of reactions includes the important examples of ammonia and methanol syntheses, the Fischer-Tropsch and oxo and synthol processes and the production of alcohols, aldehydes, ketones, amines, and edible oils. 

From this discussion it will be clear that supported, or dispersed, transition group oxide systems may be studied by the measurement of magnetic susceptibility. If the susceptibility is plotted against concentration for a supported oxide there are obtained curves characterized in most cases by a great increase in susceptibility at low concentration. The effect is especially pronounced at low temperatures. It is convenient to have a name for such curves. They are called susceptibility isotherms. In many cases the susceptibility rises sharply at a critical point, conveniently referred to as point 1. ... 

If this were the only example of diminished mi netic moments, then such an explanation in terms of intercation covalency would be indefensible. But the effect actually occurs with most of the transition group oxides. Even in supported chromia the measured moment is about 10 per cent too small, while in molybdenum dioxide the expected moment of 2.8 Bohr magnetons is actually found to be zero. Other examples of the effect will be mentioned later. 

The considerations described in preceding pages apply to transition group oxides on the surface of diamagnetic, high-area supports. It is a surprise to find that some of the same magnetic phenomena may be observed in the absence of the support. 

Rare earths in iron transition group oxides... 

For the heavier congenors, tungsten in the group oxidation state is much more stable to reduction, and it is apparently the last element in the third transition series in which all the 5d electrons participate in metal bonding. 

In moving across the transition series, iron is the first element which fails to attain its group oxidation state (-1-8). The highest oxidation state known (so far) is 4-6 in [Fe04] and even this is extremely easily reduced. On the... 

Dithiocarbamates of transition group elements in unusual oxidation states. J. Willemse, J. A. Cras, J. J, Steggerda and C. P. Keijzers, Struct. Bonding (Berlin), 1976, 28, 83-126 (195). 

Dithiocarbamates of Transition Group Elements in Unusual Oxidation States... 

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