STM investigation and Monte-Carlo modelling of spillover in a supported metal catalyst

Here we show, by in situ scanning tunnelling microscopy, that Pd nanopartic les enhance the rate of re-oxidation of a sub-stoichiometric TiO2(1 1 0) su rface. We believe that O-2 dissociatively adsorbs at 673 K on the Pd, and " spills over" onto the support where further reaction takes place. Tin+ inte rstitial ions in the bulk crystal lattice react with the spillover oxygen a t the surface, preferentially growing TiO2 around and over the particles. W e employ a kinetic Monte-Carlo scheme to simulate this surface reaction and find a good correlation between the simulation and STM images. The simulat ion indicates that the surface structure may be reproduced in a model in wh ich mobile species spillover from the metal particle, performs a random wal k until it reaches a step edge where it may react (with low probability) to form TiO2 The mobile species may also down-step to a lower terrace but up- stepping is forbidden. The temporal evolution of surface structures from bo th experiment and simulation are compared. (C) 2001 Elsevier Science B.V. A ll rights reserved.