(457a) Reactions of Methanol and Ethylene Glycol On Ni/Pt: Bridging the Materials Gap Between Single Crystal and Polycrystalline Bimetallic Surfaces

The catalytic decompositions of methanol and ethylene glycol on bimetallic polycrystalline Ni/Pt surfaces were studied as model probe reactions for the reforming of oxygenates. There are two well characterized monolayer surface structures for the Ni/Pt system [1]: the surface configuration, in which the Ni atoms reside primarily on the surface of the polycrystalline Pt, and the subsurface configuration, in which the second atomic layer is enriched in Ni atoms and the surface is enriched in Pt atoms. These configurations are denoted NiPtPt and PtNiPt, respectively. This study aimed to bridge the ?materials gap? and determine if favorable reforming activity observed in single crystal studies of the Ni/Pt system are relevant to more practical polycrystalline materials.

Consistent with single crystal studies [2, 3], temperature programmed desorption (TPD) studies revealed that the NiPtPt surface was more active to methanol and ethylene glycol reforming than the Pt or PtNiPt surfaces. High resolution electron energy loss spectroscopy (HREELS) confirmed the presence of strongly bound reaction intermediates [4], including aldehyde-like species [2], and suggested that the first decomposition step of both oxygenates was likely O-H bond scission. Thus, the binding energies of the deprotonated reaction intermediates are likely important parameters in controlling the decomposition of oxygenates. In contrast to single crystal studies [3], the PtNiPt surface showed higher reforming activity than Pt for methanol and ethylene glycol decomposition. This is likely due to the incomplete diffusion of Ni atoms into the subsurface region on polycrystalline Pt.

Overall, this study suggested that the polycrystalline Ni/Pt systems behaved similarly to the single crystal analogues. The surface configuration showed the highest reforming activity in both single crystal and polycrystalline studies and a supported catalyst based on this system could prove to be an effective catalyst for oxygenate reforming. Furthermore, studies of methanol and ethylene glycol have provided a knowledge base for future research into the catalytic decompositions of larger polyols, such as glycerol and sorbitol.

[1] J. G. Chen, C. A. Menning, M. B. Zellner, Surface Science Reports 63 (2008) 201

[2] O. Skoplyak, C. A. Menning, M. A. Barteau, J. G. Chen, Journal of Chemical Physics 127 (2007) 114707.

[3] O. Skoplyak, M. A. Barteau, J. G. Chen, Journal of Physical Chemistry B 110 (2006) 1686.

[4] A. L. Stottlemyer, H. Ren, J. G. Chen, Surface Science (submitted).