The geometrical structure of the Au‐Fe2O3interfacial perimeter, which is generally considered as the active sites for low‐temperature oxidation of CO, was examined. It was found that the activity of the Au/Fe2O3catalysts not only depends on the number of the gold atoms at the interfacial perimeter but also strongly depends on the geometrical structure of these gold atoms, which is determined by the size of the gold particle. Aberration‐corrected scanning transmission electron microscopy images unambiguously suggested that the gold particles, transformed from a two‐dimensional flat shape to a well‐faceted truncated octahedron when the size slightly enlarged from 2.2 to 3.5 nm. Such a size‐induced shape evolution altered the chemical bonding environments of the gold atoms at the interfacial perimeters and consequently their catalytic activity. For Au particles with a mean size of 2.2 nm, the interfacial perimeter gold atoms possessed a higher degree of unsaturated coordination environment while for Au particles with a mean size of 3.5 nm the perimeter gold atoms mainly followed the atomic arrangements of Au {111} and {100} facets. Kinetic study, with respect to the reaction rate and the turnover frequency on the interfacial perimeter gold atom, found that the low‐coordinated perimeter gold atoms were intrinsically more active for CO oxidation.18O isotopic titration and Infrared spectroscopy experiments verified that CO oxidation at room temperature occurred at the Au‐Fe2O3interfacial perimeter, involving the participation of the lattice oxygen of Fe2O3for activating O2and the gold atoms for CO adsorption and activation.
A plasmonic flow reactor, consisting of thin Au film at exits of monolithic anodized aluminum oxide (AAO) membranes under LED illumination is demonstrated. The system shows over 200% quantum efficiency (QE) for peroxide activation and the ability to limit to single oxidation reaction by controlling residence time with flow rate and pore geometry. Periodic pore arrays (20–200 nm diameter) with 25 nm thick Au on AAO are modeled by finite‐difference time‐domain (FDTD) simulations and predicted largest E‐field enhancements for the larger 200 nm pore diameters. Peroxide activation, as measured by O2generation is most efficient with a 200 nm pore diameter system under 523 nm LED illumination. The optimal wavelength falls near the absorption peak of Au@AAO with 200 nm pore diameter suggesting that hot electron generated from gold plasmonic response is the primary mechanism for activation of H2O2. QE for gold plasmonic flow system calculated from O2generation experiments is as high as 250%, which indicates a mechanism of hot‐electron activation of peroxide that leaves a still energetic hot‐electron to catalytically activate multiple reactions. The formation of Au surface oxides that are catalytically active in dark is also observed and must be accounted for in Au plasmonic photochemical studies.
more » « less- NSF-PAR ID:
- 10450761
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Functional Materials
- Volume:
- 31
- Issue:
- 23
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The geometrical structure of the Au‐Fe2O3interfacial perimeter, which is generally considered as the active sites for low‐temperature oxidation of CO, was examined. It was found that the activity of the Au/Fe2O3catalysts not only depends on the number of the gold atoms at the interfacial perimeter but also strongly depends on the geometrical structure of these gold atoms, which is determined by the size of the gold particle. Aberration‐corrected scanning transmission electron microscopy images unambiguously suggested that the gold particles, transformed from a two‐dimensional flat shape to a well‐faceted truncated octahedron when the size slightly enlarged from 2.2 to 3.5 nm. Such a size‐induced shape evolution altered the chemical bonding environments of the gold atoms at the interfacial perimeters and consequently their catalytic activity. For Au particles with a mean size of 2.2 nm, the interfacial perimeter gold atoms possessed a higher degree of unsaturated coordination environment while for Au particles with a mean size of 3.5 nm the perimeter gold atoms mainly followed the atomic arrangements of Au {111} and {100} facets. Kinetic study, with respect to the reaction rate and the turnover frequency on the interfacial perimeter gold atom, found that the low‐coordinated perimeter gold atoms were intrinsically more active for CO oxidation.18O isotopic titration and Infrared spectroscopy experiments verified that CO oxidation at room temperature occurred at the Au‐Fe2O3interfacial perimeter, involving the participation of the lattice oxygen of Fe2O3for activating O2and the gold atoms for CO adsorption and activation.
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