Oxygen in oxidations

Todorova M, Li WX, Ganduglia-Pirovano MV, Stampfl C, Reuter, Scheffler M. 2002. Role of subsurface oxygen in oxide formation at transition metal surfaces. Phys Rev Lett 8909 6103. 

It is an important role plaid by singlet oxygen in oxidizing organic substances that does determine the interest in the study of interaction between 02( A ) and the surface of these substances. Application of... 

These effects are most striking on silver since it is, itself, a very unreactive surface. There is every reason to expect, however, that oxygen will behave similarly on other metals. More complex reaction behavior will, of course, be observed as the intrinsic reactivity of the metal increases. Oxygen adsorbed on platinum should show similar properties. In fact the formation of surface OH groups from HjO and 0(a) was recently reported 145). The ability of platinum itself to break C-H and C-C bonds complicates oxidation mechanisms, but future work should provide a greater understanding of the relative role of surface oxygen in oxidation catalysis. 

Air is the most common carrier gas in environmental applications, whereas nitrogen and helium are frequently used in laboratory experiments. Furthermore, oxygen in oxidations and hydrogen in hydrogenations are often used as reactants. Consequently, the most important properties of these gases among others are presented hereinafter. 

It can be seen that the first conversion is relatively thermodynamically feasible. Thus, from the discussion above, the Fe ion in a selective oxidation catalyst should be near the fully oxidized state such that it can undergo the necessary reduction-oxidation cycle easily. It is significant to note that there is a substantial difference in the thermodynamic driving force (or resistance) between the first and the second reduction. This could be important in controlling the amount and the reactivity of the lattice oxygen in oxidation reactions. 

The general conclusion from this work is that there is considerable mobility of surface oxygen in oxide catalysts at temperatures around 200° and upwards. On Mn02/Mn203, CuO, and Fe304, the oxidation of CO by 02 occurs by alternate reduction and oxidation of the catalyst surface so that oxygen from the oxide lattice appears in the product. (The possibility of a rapid exchange of the C02 with the catalyst surface is not, however, completely excluded.)... 

Total weight of black oxide = 3.978 g Weight of copper in oxide = 3.178 g Weight of oxygen in oxide = 0.800 g... 

S9a) Koch, W., Lemm, H. Direct determination of oxygen in oxide materials. Arch. Eisen-hiittenw. 39, 823 (1968). - Anal. Abstr. 18, 893 (1970). 

Table II. Crystal Structure and Mossbauer Spectral Parameters for Ferric Iron Coordinated to Oxygen in Oxide and Silicate Minerals...

Figure 10. Chemical state plot for oxygen in oxides and hydroxides ( i i). Numbers represent the number of compounds included in the area.

Although HRTEM has atomic resolution, most images of oxides show only metal atoms, as oxygen s contribution to the image contrast is not significant. As a result of the development of Cs-corrected TEM, it has become possible to see directly oxygen atoms [13]. Even then, determination of the positions and occupation factors of oxygen in oxides still has to be rely on diffraction methods. 

Table CLIX. Coordination Number of Oxygen in Oxides...

The structural chemistry of V in various oxidation states (ii-v) in binary compounds has been noted in previous chapters, in particular the unusual coordination of V(v) by oxygen in oxides and oxy-salts, where there is very irregular square pyramidal or octahedral coordination (in addition to tetrahedral coordination). Our chief concern here is with compounds of V(iv), but we shall mention incidentally several complexes of V(iii) and V(v). 

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