| AVS 61st International Symposium & Exhibition | |
| Nanometer-scale Science and Technology | Wednesday Sessions |
| Session NS-WeM |
| Session: | Nanoscale Catalysis and Surface Chemistry |
| Presenter: | Monica McEntee, University of Virginia |
| Authors: | M. McEntee, University of Virginia W. Tang, University of Virginia M. Neurock, University of Virginia J.T. Yates, Jr., University of Virginia |
| Correspondent: | Click to Email |
Gold nanometer diameter particles supported on reducible oxide supports exhibit catalytic activity at temperatures as low as 90 K.[1] Numerous studies[2-4] have theorized that the catalytic activity occurs at the metal-support interfacial sites. In 2011, Green et al.[5] discovered, using infrared (IR) spectroscopy, a dual catalytic site for molecular oxygen adsorption and subsequent activation with one O atom bonded to the Au and the other O bonded to the Ti4+ site of the TiO2 support. Here I show, using IR spectroscopy and density functional theory (DFT), the oxidation of three carboxylic acids (acetic, propionic and butyric acid) on a Au/TiO2 catalyst with ~3 nm diameter Au nanoparticles producing gold ketenylidene, Au2C=C=O, species. The initial step in all three acid oxidation processes is the dissociation of O2 at the Au-Ti4+ dual site to form reactive O adatoms at the interface. Next, in sequential steps, α-CH and β -CH bonds specifically next to the COO group in each acid are oxidatively dehydrogenated to produce unsaturated, C=C, species. C-C and C-O bond scission occur next yielding adsorbed ketenylidene, Au2C=C=O, an exotic species formed just before full oxidation. Control oxidation experiments on the TiO2 support alone produce no Au2C=C=O species verifying the reaction occurs at the Au/TiO2 interface. Also, isotopically-labelled O2 and acid experiments confirm the Au2C=C=O is composed of specifically α-C and β -C atoms and O atoms from the acid.
References
1. Haruta, M.; Kobayashi, T.; Sano, H.; Yamada, N. Novel gold catalysts for the oxidation of carbon monoxide at a temperature far below 0 oC. Chem. Lett. 1987, 405-408.
2. Rodriguez, J.; Ma, S.; Liu, P.; Hrbek, J.; Evans, J.; Perez, M. Activity of CeOx and TiOx nanoparticles grown on Au (111) in the water-gas shift reaction. Science 2007, 318, 1757-1760.
3. Molina, L.; Rasmussen, M.; Hammer, B. Adsorption of O2 and oxidation of CO at Au nanoparticles supported by TiO2(110). J. Chem. Phys. 2004, 120, 7673.
4. Camellone, M. F.; Zhao, J.; Jin, L.; Wang, Y.; Muhler, M.; Marx, D. Molecular Understanding of Reactivity and Selectivity for Methanol Oxidation at the Au/TiO2 Interface. Angew. Chem., Int. Ed. 2013 , 52 , 5780 − 5784.
5. Green, I. X.; Tang, W.; Neurock, M.; Yates Jr., J. T. Spectroscopic observation of dual catalytic sites during oxidation of CO on a Au/TiO2 catalyst. Science 2011, 333, 736-739.