Platinum Metals Rev., 1990, 34, (2), 73
Complete Oxidation of Organics
Catalysis Volume 8, Specialist Periodical Reports Edited By G. C. Bond and G. webb, The Royal Society of Chemistry, 1989, 203 pages, ISBN 0-85186-594-1, £70.00, U.S.$134.00
As may well be expected, any book on catalysis is almost certain to contain many references to the uses of the platinum metals and this is especially true if, as in the present case, one whole chapter is devoted to the complete catalytic oxidation of volatile organic molecules. Altogether the present volume contains five chapters of approximately equal length, including one devoted to catalysis by solid acids and bases, two on theoretical studies of the structure of the catalytic site in zeolites and on oxide/metal surfaces, and a fifth on the use of EXAFS in the study of catalysts.
The chapter on EXAFS starts with a brief but useful description of the underlying theory and type of equipment used for making measurements. Information can be obtained which is extremely pertinent to two main problems: the specific detailed environment of a given atom, for example the ligand donor set of a given metal centre, or secondly, the morphology and atomic packing of small metal particles. Intermediate between these would be the structure and integrity of small metal cluster compounds such as are sometimes used in catalyst preparation. Details are given of work in all these areas. Particularly relevant to the platinum metals is the work described on the structures of osmium and rhodium carbonyl cluster compounds and, together with similar ruthenium complexes, their fate when impregnated on typical silica or alumina catalyst supports. The cationic exchange of metals onto zeolites can also be followed, as can the development of metal and metal alloy particles during reduction.
The chapter on complete oxidation of organics is less informative and therefore less satisfactory. Again there is an introductory section but this is both too long and too elementary for a Specialist Report. This chapter is more a review of catalytic combustion rather than a review of recent literature. Of the 125 references quoted more than 20 predate the 1970s and less than 50 appeared in the 1980s. For the enthusiast there is a Table extending for some twenty pages which lists, apparently in random order, a selection of systems which have been reported in terms of conditions and catalyst used, and the nature of the reactant. Less than one page of text is devoted to a discussion of applications.
Major problem areas identified with this type of oxidation include the possibility of producing more toxic products by partial combustion; for example, dioxins from incomplete combustion of chlorinated compounds and also the poisoning of the catalyst by sulphur or chlorine, and fouling of the catalyst by other components which can give rise to an inorganic ash. Problems also arise when trying to predict conditions for the combustion of mixtures since both synergistic and antagonistic interactions can occur.