Different support effect of M/ZrO2 and M/CeO2 (M=Pd and Pt) catalysts on CO adsorption:: A periodic density functional study

CO adsorption over Pd-4 and Pt-4 cluster supported by c-ZrO2(1 1 1)and CeO2(1 1 1) catalyst systems was investigated using periodic density functional method in order to clarify the support effect on CO activation. We found that the support increases the CO activation for bridge and threefold sites but decreases for the atop site. Moreover, it was found that the support changes the site preference for the CO adsorption. Bridge site on both the Pt-4/c-ZrO2 and Pt-4/CeO2 show larger CO adsorption energies than those on the other sites while the atop site is energetically preferable on isolated Pt-4 cluster. c-ZrO2 supported Pd shows the largest CO activation with large charge transfer from the catalyst to the CO molecule. This reveals that ZrO2 supported Pd can be a good catalyst for CO activation because of its higher probability to the three-fold site CO adsorption. We also found that positively charged M-4 clusters on the support keep their strong electron-donating properties and have enough charge density to contribute to the activation of an adsorbed CO molecule by a charge transfer. (c) 2005 Elsevier B.V. All rights reserved.