Chemistry

Supports for Mechanisms

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Science  14 Jan 2011:
Vol. 331, Issue 6014, pp. 127
DOI: 10.1126/science.331.6014.127-b

The mechanism of the low-temperature oxidation of CO by gold nanoclusters on oxide supports could depend on whether the oxide is a reducible metal, such as iron or titanium, or a nonreducible one, such as zinc. Carley et al. studied the oxidation of CO by gold nanoparticles supported on Fe2O3 and ZnO. The catalysts were exposed to a transient pulse of reactants (CO and O2) in an argon carrier at room temperature. When the catalysts were predosed with 18O-labeled water to form labeled surface hydroxyl groups, the initial CO2 product that formed on the zinc oxide support carried all three possible isotope distributions, but on iron oxide support, the initial CO2 product was fully 18O-labeled. These results are consistent with the formation of a nondissociative bicarbonate intermediate on the zinc oxide support, contrasting with a CO dissociation mechanism on iron oxide, where the adsorbed carbon reacts with surface hydroxyls. This dissociative mechanism is supported by x-ray photoelectron spectra, which showed the formation of adsorbed carbon after exposure to CO and O2 (but not CO alone). Density functional theory calculations show that oxidation of the gold atoms at the edge of the adsorbed clusters, along with the formation of surface bonds, can compensate for the high energy input needed to cleave CO and O2.

Phys. Chem. Chem. Phys. 13, 10.1039/c0cp01852j (2011).

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