FROM SURFACE SCIENCE TO CATALYSIS - SURFACE EXPLOSIONS OBSERVED ON RH CRYSTALS AND SUPPORTED CATALYSTS

Phenomena called surface ''explosions'' have been reported for decomposition reactions on single crystals, and have been identified by the use of desorption methods. In particular, in TPD, they are manifested by extremely narrow peaks (as little as 3 K in width) and a desorption rate which increases with time in isothermal experiments. In this paper we report such observations for acetate species on Rh single crystals, but extend this to show for the first time that such effects are not restricted to single crystal/UHV experiments, but can also be found on a Rh/Al2O3 catalyst under ambient pressure conditions. These reactions can be classified as second order autocatalytic surface processes, where free surface Rh sites are an essential component of the reaction. It is shown that coadsorbed adatoms are also essential for such ''explosions'' to be seen and their role is proposed to be that of a template layer acting to order the acetate in self-poisoning configurations.