(654c) A Novel Multilayer Infrared Absorption Spectroscopy (MEIRAS) Technique for Infrared Polarization Dependent Operando Study CO Adsorption and Oxidation On Thin Film and Nanowire Catalysts

We have developed a new multilayer enhanced infrared reflection absorption spectroscopy (MEIRAS) technique for study of adsorbates, on catalyst such as thin films and low area supported nanoparticles or nanowires [1].  The MEIRAS technique utilizes the optical interference effects in metal-dielectric-metal multilayer substrate to obtain a large signal enhancement by quarter-wave matching of dielectric layer thickness to desired infrared wavelength.  These effects have been studied using optical simulation and a thorough theoretical analysis.  The sensitivity enhancement through multilayer reflection, combined with the experimental setup developed here, provides unique capability for high pressure FTIR study of adsorption and reactions on low area model catalysts.  Unlike commonly used techniques for these studies (such as PM-IRAS and SFG), this technique does not require additional optical instrumentation apart from a standard FTIR setup.  Moreover, it is sensitive to both surface normal and tangential vibrational modes [2].  This is in contrast to IRAS techniques on reflecting metal substrates which only detect normal modes. 

In the present work, we perform CO adsorption and oxidation study using MEIRAS on TiO₂ supported Pt thin film and nanofabricated parallel monodisperse nanowires under reaction conditions.  The effect of the width of nanowires on CO infrared absorption band position and surface ignition behavior of CO oxidation reactions is studied.  With incident infrared polarized either along the Pt nanowires or normal to nanowires, signal can be selectively collected from CO molecules adsorbed either on top of the wires or on the edges of the wires.  On analyzing these spectra we find that infrared absorption peak on CO adsorbed on the edges of wire, closer to the Pt/TiO₂ interfaces is slightly red shifted compared to the signal from top of the wire, indicating the role support effects.  These experiments highlight the role of metal-support interfaces in catalysis and provide a way to selectively probe adsorbates at or near these interfaces.

References:

[1] P Deshlahra et al. Surf. Sci. 604, 2 (2010);  P Deshlahra et al. Appl. Catal. A 391, 22 (2011).

[2] P Deshlahra and EE Wolf J. Phys. Chem. C 114, 16505 (2010).