| AVS 59th Annual International Symposium and Exhibition | |
| In Situ Microscopy and Spectroscopy Focus Topic | Tuesday Sessions |
| Session IS+AS+SS+EN-TuM |
| Session: | In Situ Spectroscopic Studies of Catalysis and Gas-Solid Reactions |
| Presenter: | S. Axnanda, Lawrence Berkeley National Laboratory |
| Authors: | S. Axnanda, Lawrence Berkeley National Laboratory Z. Liu, Lawrence Berkeley National Laboratory B. Mao, Lawrence Berkeley National Laboratory |
| Correspondent: | Click to Email |
Heterogeneous catalysts consisting of small particles having a high concentration of structural defects and under-coordinated sites make up the majority of the catalytic processes in industrial chemistry. One important recent example of interest shows that the interface-confined coordinatively unsaturated ferrous (CUF) sites together with the metal supports (FeO1-x/Pt(111)) are active for dioxygen activation which causes the ensemble to be highly efficient for CO oxidation at low temperature under typical operating conditions of a proton-exchange membrane fuel cell.[1-2] In this work, we report another spectroscopic evidence to further confirm an enhanced reactivity at the edges of small catalyst particles. The system in interest is partially oxidized SnOx (Sn2+) nanoislands supported on Pt(111) for ethanol oxidation reaction (EOR), an electrode material in a direct alcohol fuel cell (DAFC). Our findings suggested that SnOx/Pt(111) inverse catalysts have improved activity for EOR in acidic media as compared to a bare Pt(111) surface.[3] We also found that the most active surface had a small coverage of SnOx (0.3- 0.4 ML). Water activation at low potentials is currently attributed to be the promoting effect of SnOx nanoparticles, since this enhances the oxidation of chemisorbed CO formed on Pt sites during the EOR.[4] To better understand this increased activity, we performed study with the goal to indicate the actual state of Sn in SnOx nanoislands before and after the SnOx /Pt(111) is used in EOR showing the increased activity: purely oxide Sn or mixed Sn alloy and Sn oxide, using a combination of APXPS and XANES techniques. BE shift in the XPS core-line spectra of Sn and O, soft X-ray XANES spectra (Sn M4,5-edge, O K-edge) will be collected and compared to the corresponding XPS spectra (Sn 3d, O 1s) to explain the actual state of Sn before and after the SnOx/Pt(111) is used in the EOR.
1. Fu, Q., et al., Interface-Confined Ferrous Centers for Catalytic Oxidation. Science, 2010. 328: p. 1141.
2. Deng, X., et al., Reactivity Differences of Nanocrystals and Continuous Films of α-Fe2O3 on Au(111) Studied with In Situ X-ray Photoelectron Spectroscopy. J. Phys. Chem. C, 2010. 114: p. 22619.
3. Zhou, W.P., et al., Enhancement in Ethanol Electro-Oxidation by SnOx Nanoislands Grown on Pt(111): Effect of Metal Oxide-Metal Interface Sites. Journal of Physical Chemistry C, 2011. 115: p. 16247.
4. Axnanda, S., W.P. Zhou, and M.G. White, CO Oxidation on Nanostructured SnOx/Pt(111) surfaces: Unique Properties of Reduced SnOx. Phys. Chem. Chem. Phys, 2012. Submitted.