AVS 49th International Symposium
    Surface Science Monday Sessions
       Session SS2-MoM

Paper SS2-MoM7
Examination of the Redox Chemistry of Water with the Oxidized and Reduced Surfaces of CeO@sub 2@(111)

Monday, November 4, 2002, 10:20 am, Room C-112C

Session: Oxide Structure and Surface Chemistry
Presenter: M.A. Henderson, Pacific Northwest National Laboratory
Authors: M.A. Henderson, Pacific Northwest National Laboratory
M.H. Engelhard, Pacific Northwest National Laboratory
C.H.F. Peden, Pacific Northwest National Laboratory
C.L. Perkins, Pacific Northwest National Laboratory
S. Thevuthasan, Pacific Northwest National Laboratory
Correspondent: Click to Email
Ceria is important in automotive three-way catalysts because of its ability to store and release oxygen as reaction conditions oscillate between oxidizing and reducing conditions. The effect of such redox oscillations on adsorbate chemistry is not well understood, although the chemistry of water on oxide surfaces is known to depend on the surface's redox state.@footnote 1@ Two groups have recently reported conflicting results for the interaction of water with reduced CeO@sub 2@(111) films, with one group reporting Ce@super 3+@ oxidation@footnote 2@ and the other reporting Ce@super 4+@ reduction.@footnote 3@ In both cases, the CeO@sub 2@(111) films were thin (@<=@ 50 Å) and were grown on metal substrates (Ru(0001)@footnote 2@ and Pt(111)@footnote 3@). We have studied the interaction of water with a 500 Å CeO@sub 2@(111) film grown on Y-stabilized ZrO@sub 2@(111). TPD measurements for varying coverages of water on either oxidized (800 K in O@sub 2@) or vacuum reduced (at 850 K) CeO@sub 2@(111) are suggestive of predominately molecularly adsorbed water, and show no evidence for irreversible decomposition either in terms of water consumption or H@sub 2@/O@sub 2@ desorption. Complimentary core and valence band photoemission results show that adsorbed water does not increase or decrease the level of Ce@super 3+@ in the reduced CeO@sub 2@(111) surface, although water exposure at 600 K shows a slight increase in Ce@super 3+@ over that seen from annealing in UHV at the same temperature. Comparison of our results for the CeO@sub 2@/ZrO@sub 2@(111) system with those from thin CeO@sub 2@ films grown on metal substrates suggests that metal substrates may participate in water redox chemistry on ceria. @FootnoteText@ @footnote 1@ M.A. Henderson, Surf. Sci. Rep. 46 (2002) 1.@footnote 2@ Lj. Kundakovic et al., Surf. Sci. 457 (2000) 51.@footnote 3@ U. Berner et al., Surf. Sci. 467 (2000) 201.