Controlled preparation of heterogeneous catalysts for chemo and enantioselective hydrogenation reactions

OSMAR A. FERRETTI; MÓNICA L. CASELLA

Modern Surface Organometallic Chemistry

Wiley-VCH Verlag GmbH & Co

Lugar: Weinheim (Alemania); Año: 2009; p. 239 - 291

In this contribution, Surface Organometallic Chemistry on Metals (SOMC/M) will be used to study the reactivity of organometallic complexes with the surface of supported metals. In 1984, Travers [28] and Margitfalvi [29] simultaneously described this application of surface organometallic chemistry for the preparation of bimetallic catalysts. By applying this technique, it is not only possible to prepare relatively well-defined catalysts that may be alloys of a given composition, but also catalysts in which adatoms of main group elements may be located on the surface of transition metal particles or ‘organometallic fragments’ that are likely adsorbed (coordinated) at some particular crystallographic positions of the metallic particles. It has been shown that each of these three different types of materials exhibits interesting and unusual selectivities in many catalytic reactions [30, 31]. Thus, for instance, it has been shown that the partial hydrogenolisis of tetra n-butyl tin anchored to the surface of a noble metal such as Rh or Pt supported on silica leads to an organobimetallic catalyst with remarkable activity and selectivity in hydrogenation reactions of unsaturated carbonyl compounds [32]. The total hydrogenolisis of tetra n-butyl tin on silica- or alumina-supported rhodium, ruthenium, platinum, copper or nickel particles leads to bimetallic catalysts that are very active and selective in a range of reactions, such as ethyl acetate hydrogenolysis into ethanol [17, 33], NO-H2 reaction [34], syngas production via methane partial oxidation [35] and hydrogenolysis and dehydrogenation of paraffins [36-38]. The research groups working with this technique have successfully characterised the bimetallic materials obtained, by means of various physical techniques, correlating the structure of the active phase with the catalytic behaviour [24, 26, 27, 39-41]. Special mention should be made of organobimetallic catalytic phases where one or more of the organic fragments have chiral characteristics. In this case, by using SOMC/M techniques, heterogeneous chiral catalysts of very good quality in terms of chemo- and enantioselectivity, as well as good stability and reuse capability, were obtained [42, 43]. The present work reports on the controlled route for the preparation and characterisation of bi- and organobimetallic catalysts via SOMC/M techniques, as well as some interesting applications in reactions requiring high activity as well as chemo‑ and enantioselectivity.