AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM4
Attenuated Total Reflection Infrared Spectroscopy and Nanoparticles: A New Tool for Probing Adsorption (CO, NH@sub 3@) on Planar Model Catalysts (Rh)

Tuesday, November 1, 2005, 9:20 am, Room 202

Session: Vibrational Spectroscopy of Surfaces
Presenter: C.M. Leewis, Eindhoven University of Technology, The Netherlands
Authors: C.M. Leewis, Eindhoven University of Technology, The Netherlands
M.C.M. Van De Sanden, Eindhoven University of Technology, The Netherlands
W.M.M. Kessels, Eindhoven University of Technology, The Netherlands
J.W. Niemantsverdriet, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
Attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR) is used to study adsorption and/or decomposition of CO and NH@sub 3@ on Rh nanoparticles. The silicon ATR crystal (25 reflections, 45°) with a 50 nm thick hydroxylated thermal SiO@sub 2@ layer acts as the support for the nanoparticles. These are spincoated from a RhCl@sub 3@ solution in water followed by reduction in H@sub 2@ at 200°C. X-ray Photoelectron Spectroscopy (XPS) shows the reduction to Rh@super 0@ and the removal of Cl. Atomic Force Microscopy (AFM) shows a distribution of 200 particles per µm@super 2@, which are ~3 nm in height. The ATR-FTIR experiments are performed in UHV without exposing the crystal bevels and backside (both without oxide and Rh) to the gases. For a 4 cm@super -1@ resolution, a sensitivity of reflectance as low as 5x10@super -5@ absorbance units in the region 2000-3500 cm@super -1@ can be reached. CO exposure validates the detection of species on the nanoparticles, since CO does not interact with the support. Linearly adsorbed CO on Rh is observed at 2023 cm@super -1@. No bridged CO or geminal dicarbonyls are observed. For ammonia, interaction with the silica OH groups is observed around 2900 cm@super -1@ in combination with negative unperturbed OH peaks between 3500 and 3700 cm@super -1@. In addition, N-H bend (1634 cm@super -1@) and stretch (3065, 3197 cm@super -1@) vibrations are observed for substrate temperatures between 20°C and 150°C. The latter correspond to N-H on Rh, as verified with a sample without Rh, and remained after evacuation, suggesting strongly bound species. For 75°C and 100°C, additional peaks at 3354 and 3283 cm@super -1@ are observed, possibly due to NH@sub 2@ intermediates. ATR-FTIR is therefore a powerful technique for probing adsorbates on supported nanoparticles.