| AVS 59th Annual International Symposium and Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS-WeM |
| Session: | Chemisorption on Metallic Surfaces |
| Presenter: | M.H.C. Van Spyk, University of California Irvine |
| Authors: | M.H.C. Van Spyk, University of California Irvine K.A. Perrine, University of California Irvine J.C. Hemminger, University of California Irvine |
| Correspondent: | Click to Email |
Factors such as support type and nanoparticle morphology are known to impact catalytic activity, but detailed studies are required to elucidate the effect of nanoparticle size on the mechanism of dehydrogenation over nanoparticles supported on oxides. In this work, high resolution electron energy loss spectroscopy (HREELS) was used to characterize the dehydrogenation of hydrocarbons on platinum nanoparticles supported on an Al2O3 film grown by oxidation of a NiAl(110) single crystal. The alumina film is a good representation of the high surface area oxides used as catalyst supports in industry, and the flat surface enables investigation by electron inelastic scattering techniques. The platinum nanoparticles were deposited on a fresh alumina film at cryogenic temperatures, and platinum deposition was monitored by the reduction in elastic peak intensity in the HREEL spectra. Cyclohexane was used as a model hydrocarbon because the dehydrogenation on Pt(111) has been studied extensively and thus provides a good point of comparison for the nanoparticle studies. The HREELS spectra of cyclohexane on Pt(111) show a distinct low frequency peak at 2600 cm-1 which can be monitored to determine the temperature at which dehydrogenation begins.1,2 The HREELS annealing profile from an alumina film does not exhibit cyclohexane adsorption at 170 K, or upon successive annealing. In contrast, the HREEL spectra from platinum nanoparticles on alumina exhibit cyclohexane adsorption at 170 K with the νC-H stretch energy loss peak observed at 2930 cm–1. Interestingly, HREEL spectra from cyclohexane on platinum nanoparticles do not resemble spectra from cyclohexane on Pt(111). Specifically, the additional νC-H energy loss peak observed at 2600 cm-1 for cyclohexane adsorbed on Pt(111) is not seen in the case of platinum nanoparticles.1,2 In addition, the νC-H energy loss peak from cyclohexane on platinum nanoparticles does not shift or decrease in intensity upon annealing to room temperature. Our results indicate that cyclohexane dehydrogenates upon adsorption to platinum nanoparticles at 170 K. This dehydrogenation temperature is lower than that on Pt(111), indicating that platinum nanoparticles supported on an alumina film are more catalytically active for the initial stages of dehydrogenation than Pt(111).
1. Land, D. P.; Erley, W.; Ibach, H., HREELS Investigation of the Orientation and Dehydrogenation of Cyclohexane on Pt(111). Surface Science 1993, 289 (3), 237-246.
2. Saeys, M.; Reyniers, M. F.; Neurock, M.; Marin, G. B., Adsorption of cyclohexadiene, cyclohexene and cyclohexane on Pt(111). Surface Science 2006, 600 (16), 3121-3134.