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

Phenomena called surface ''explosions'' have been reported for decompo sition reactions on single crystals, and have been identified by the u se of desorption methods. In particular, in TPD, they are manifested b y extremely narrow peaks (as little as 3 K in width) and a desorption rate which increases with time in isothermal experiments. In this pape r we report such observations for acetate species on Rh single crystal s, but extend this to show for the first time that such effects are no t restricted to single crystal/UHV experiments, but can also be found on a Rh/Al2O3 catalyst under ambient pressure conditions. These reacti ons can be classified as second order autocatalytic surface processes, where free surface Rh sites are an essential component of the reactio n. It is shown that coadsorbed adatoms are also essential for such ''e xplosions'' to be seen and their role is proposed to be that of a temp late layer acting to order the acetate in self-poisoning configuration s.