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Zawartość zarchiwizowana w dniu 2024-05-29

New directions in heterogeneous selective oxidation catalysis: synthesis and application of novel metal nanoparticulate systems

Final Activity Report Summary - BINACAT (New directions in heterogeneous selective oxidation catalysis: synthesis and application of novel metal nanoparticulate systems)

Catalysts are substances that speed up chemical reactions. They are vitally important both in the research laboratory and in industry. Heterogeneous catalysts are solid substances upon whose surfaces the catalytic reaction between adsorbed molecules takes place. As an indication of the enormous technical and economic importance of heterogeneous catalysis we may note that over 95% of the output of the world's chemical industry is critically dependent on catalyzed reactions. Catalysis also provides the backbone for the global oil industry whose principal task in to refine and process crude oil to enable production of a huge range of materials from plastics to pharmaceuticals. Accordingly, deeper understanding the way in which catalysts work enables the improvement of existing catalysts or the invention of new catalysts and the discovery of new chemistry.

Three areas of particular importance are (i) selective oxidation using silver (Ag) or gold (Au) catalysts-used on a very large scale to produce strategically important chemicals that are intermediates in the production of many different substances (ii) selective hydrogenation-a key process in the production of pharmaceuticals, for example and (iii) carbon-carbon bond forming reactions that are used to build up complicated molecules from simpler molecules.

Some important classes of molecules have the ability to add on hydrogen atoms in more than one way, for example the chemical structure C=C may be converted to CH-CH and the chemical structure C=O may be converted to CH-OH. An unselective catalyst would cause both processes to occur, although frequently one wishes to catalyse the second process and not the first. This requires a selective catalyst, and is not an easy problem to solve. Our studies with copper (Cu), platinum (Pt), and platinum-zinc (PtZn) catalysts have led to the discovery of a very active and highly selective PtZn catalysts that is capable converting C=O to CH-OH while leaving unaffected the C=C structure which is present in the same molecule. The product resulting from this selective hydrogenation is of value in the production of fine chemicals, fragrances and pharmaceuticals.

Carbon-carbon bond forming reactions are of major importance and can be catalysed by a variety of metals. Much research has been devoted to the study of such processes-nearly 2,000 papers having been published on this subject over the last few years. Even so, only very few research groups have directly addressed the question-how do these catalysts actually work? In other words, what is the identity of the species that does the catalysis? There are two views about this, the majority opinion being that catalysis is due to metal-containing molecules that dissolve from the surfaces of the metal particles that are used to drive the chemistry. The minority view is that it is the metal particles themselves that do the job. By using new experimental methods we have demonstrated that in the cases of rhodium (Rh) and gold (Au) the catalysis is certainly heterogeneous-that is to say it takes place on the surfaces of the metal that is used. This goes against the majority opinion and we may expect lively discussions to arise when the papers describing our findings are published in the near future.