Heterogeneous catalysis platinum, oxygen

However, in the years after Ostwald, his former students and collaborators dominated catalysis in Germany. We can mention Bodenstein who put the study of the kinetics of heterogeneous catalysis essentially in its modern state. The Ostwald school made little contribution to mechanism, but it adhered to a view surprisingly close to that of Faraday. The famous paper of Bodenstein and Fink of 1907 interpreted the kinetics of the oxidation of sulfur dioxide on platinum in terms of the diffusion of sulfur dioxide or oxygen through a polymolecular layer of adsorbed material. In extreme cases, accord with the observed inhibition by sulfur trioxide would have required adsorbed layers so thick that they could have been pared with a razor. 

However, it is kinetically inert and requires a catalyst for this and many other of its reactions. Generally, heterogeneous catalysts such as CuO and Rh203 are used, though homogeneous catalysis has been reported for some reactions of nitric oxide. For example, a number of platinum metal complexes, as well as metals and metal oxides, can catalyze the oxygen transfer reaction ... 

Figure 7.15. NOx to N2 activity with octane as a reducing agent over silver on alumina catalyst and a platinum oxidation catalyst depending on the distance between the catalysts (K. Eranen, L.-E.Lindfors, F. Klingstedt, D.Yu.Murzin, Continuous reduction of NOx with octane over a silver/alumina catalyst in oxygen-rich exhaust gases combined heterogeneous and surface mediated homogeneous reactions, Journal of Catalysis, 219 (2003) 25).

Although the oxidation of tertiary phosphines by these catalytic processes has minimal useful application, it needs to be considered as a problematic side reaction in homogeneous catalysis. Much effort is being currently expended to immobilize platinum metal phosphine complexes on heterogenized tertiary phosphine supports, and irreversible oxidation at phosphorus on these supports effectively destroys the supported catalyst. Recent observations that the compound Rh6(CO)i6 catalyzes the oxidation of tertiary phosphines correlate with the report that phosphine oxidation occurs with molecular oxygen on Rh6(CO)i6 bound to diphenylphosphino-functionalized poly(styrenedivinylbenzene). Thus, in order to use these phosphinated polymer-supported rhodium catalysts, one needs either to rigorously exclude oxygen, or to find a way to inhibit the simultaneous catalyzed phosphine oxidation. 

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