(63h) Density Functional Study of Adsorbates and Cationic Metal/Ceria Surfaces

   M^x+/ceria catalysts
have recently been found to be active for several reactions^1,2
including CO oxidation, water-gas shift, NO reduction, and hydrocarbon
oxidation. In particular the water-gas shift reaction has the potential to
remove CO from proton-exchange membrane (PEM) fuel cell streams. The cationic
metals experimentally studied include Cu, Au, Rh, Pd, and Pt. The exact
structure of the M^x+/ceria system is unknown, but one model suggested
is the substitution of a lattice Ce⁴⁺ ions with the dopant M^x+
ions. Using density functional theory (DFT) we modeled the substitution process
of Pt and Rh in order to better understand the cationic arrangement. We also
modeled the interactions of CO with M^x+/ceria surfaces and found
carbonate-like (CO₃) species to arise upon

CO adsorption. Carbonate-like species were previously found to form on nondoped
ceria surfaces³. CO is a common molecule present during many
reactions, and thus understanding CO interactions with ceria-based catalysts is
essential for many kinetic models. We discuss the formation of the different CO
species on the doped surfaces and the relevance to the relevant catalytic
processes. We also examined the formation of hydroxyl species on the ceria
surface, which becomes important when H₂O is present.

(1) Fu, Q.; Saltsburg, H.; Flytzani-Stephanopoulos, M. Science 2003, 301, 935.

(2) Bera, P.; Patil, K. C.; Jayaram, V.; Subbanna, G. N.; Hegde, M. S. Journal
of Catalysis 2000, 196, 293.

(3) Yang, Z. X.; Woo, T. K.; Hermansson, K. Chemical Physics Letters 2004, 396,
384.