Wpływ temperatury redukcji na właściwości sorpcyjne i katalityczne naniesionych układów metalicznych

Supported noble metal catalysts are used in a large number of commercially important processes, including hydrogenation and dehydrogenation, naphtha reforming and automotive exhaust catalysis. It is a well-known fact that support influences the catalytic activity and the selectivity of the supported metal particles. The most striking effect is the so-called strong metal - support interaction (SMSI) in which a metal / support catalyst is reduced at a high temperature (773 K) and the metal loses, at least partially, its chemisorptive properties with respect to H2 and CO. This effect was first discovered by Tauster at al. on titania and then extended to other reducible supports. Several explanations have been given to account for the loss of chemisorptive and catalytic properties: the occurrence of an electronic effect with an electron transfer between the support and the metal particles, the formation of intermetallic compounds, and the decoration of the metal by support mobile species . Another model describing the metal - support interaction and based on theoretical calculations suggests that the electron density in small metal particles is shifted toward nearby cations of the support. Recently a new model has been proposed, in which the decrease in the activity of metal clusters can be ascribed to a decrease in the ionization potential of the metal particles which is directly induced by the Coulomb potential of the support .