In consideration of precursor states, spillover and Boudart's 'collection zone' and of their role in catalytic processes

Various aspects of 'spillover' and 'reverse spillover' in catalysis are con sidered. The ideas of Kisliuk regarding the kinetic role of weakly held ads orbed states as precursors to stronger chemisorption are shown to be import ant for reverse spillover, as highlighted by Boudart's concept of the 'coll ection zone'. STM has proved to be an important tool for the understanding of the formation and thermal evolution of nanoparticles on surfaces. Here w e present direct, in situ observations of spillover for the reaction of oxy gen with Pd nanoparticles on TiO2(110). In turn, this is connected to a for m of SMSI, and it is proposed that this spillover may also be the mechanism of the oxygen storage phenomenon for CeO2-doped automobile catalysts. (C) 2000 Elsevier Science B.V. All rights reserved.