Jump to main content
Jump to site search

Issue 4, 2007
Previous Article Next Article

Comparison of the reactivity of different Pd–O species in CO oxidation

Author affiliations

Abstract

The reactivity of several Pd–O species toward CO oxidation was compared experimentally, making use of chemically, structurally and morphologically different model systems such as single-crystalline Pd(111) covered by adsorbed oxygen or a Pd5O4 surface oxide layer, an oriented Pd(111) thin film on NiAl oxidized toward PdOx suboxide and silica-supported uniform Pd nanoparticles oxidized to PdO. The oxygen reactivity decreased with increasing oxidation state: O(ad) on metallic Pd(111) exhibited the highest reactivity and could be reduced within a few minutes already at 223 K, using low CO beam fluxes around 0.02 ML s−1. The Pd5O4 surface oxide on Pd(111) could be reacted by CO at a comparable rate above 330 K using the same low CO beam flux. The more deeply oxidized Pd(111) thin film supported on NiAl was already much less reactive, and reduction in 10−6 mbar CO at T > 500 K led only to partial reduction toward PdOx suboxide, and the metallic state of Pd could not be re-established under these conditions. The fully oxidized PdO nanoparticles required even rougher reaction conditions such as 10 mbar CO for 15 min at 523 K in order to re-establish the metallic state. As a general explanation for the observed activity trends we propose kinetic long-range transport limitations for the formation of an extended, crystalline metal phase. These mass-transport limitations are not involved in the reduction of O(ad), and less demanding in case of the 2-D Pd5O4 surface oxide conversion back to metallic Pd(111). They presumably become rate-limiting in the complex separation process from an extended 3-D bulk oxide state toward a well ordered 3-D metallic phase.

Graphical abstract: Comparison of the reactivity of different Pd–O species in CO oxidation

Back to tab navigation

Publication details

The article was received on 26 Jul 2006, accepted on 27 Nov 2006 and first published on 14 Dec 2006


Article type: Paper
DOI: 10.1039/B610719B
Citation: Phys. Chem. Chem. Phys., 2007,9, 533-540
  •   Request permissions

    Comparison of the reactivity of different Pd–O species in CO oxidation

    H. Gabasch, A. Knop-Gericke, R. Schlögl, M. Borasio, C. Weilach, G. Rupprechter, S. Penner, B. Jenewein, K. Hayek and B. Klötzer, Phys. Chem. Chem. Phys., 2007, 9, 533
    DOI: 10.1039/B610719B

Search articles by author

Spotlight

Advertisements