The State and Catalytic Properties of Platinum and Palladium in Faujasite-type Zeolites

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Abstract
The extensive body of literature published on the physicochemical and catalytic properties of metal zeolites has been reviewed in detail by Minachev and Isakov [1]. Industrial processes in petroleum chemistry involving metal zeolite systems have been examined by Bolton [2], Quite recently Rudham and Stockwell [3] presented a review covering many aspects of catalysis by faujasites. The scope of the present review is far more limited since only platinum and palladium faujasites will be considered and the subject will be further restricted by deliberately ignoring the important domain of bifunctional catalysis. So far little attention has been paid to the rapid progress made in the knowledge of very small particles supported on zeolites. During the past few years improved methods of particle size measurements, and new methods of evaluating the location, the structure, and the electronic properties of metal, and reliable measurements of intrinsic rates of reaction have provided much information on highly dispersed metal in zeolites which deserves to be known not only by people in the zeolite club but also by all those concerned with very small supported particles. Indeed, the choice of focusing our attention on palladium and platinum in faujasites was governed by the fact that these materials are the best known and the best suited to investigate the properties of highly divided metals. Thus, even with high loading, platinum in faujasites can be obtained in very homogeneous states of dispersion with particle sizes ranging down to nearly atomic scale. This is not true for most of the metal-zeolite systems where encaged species are always found together with unreduced cations and/or larger particles. This is not true either for platinum on other supports where wider size distribution and larger sizes are present and where minute loadings prevent detailed structural investigations.