Abstract
A new custom-designed ultrahigh vacuum (UHV) chamber coupled to a UHV and atmospheric-pressure-compatible spectroscopic and catalytic reaction cell is described, which allows us to perform IR-vis sum frequency generation (SFG) vibrational spectroscopy during catalytic (kinetic) measurements. SFG spectroscopy is an exceptional tool to study vibrational properties of surface adsorbates under operando conditions, close to those of technical catalysis. This versatile setup allows performing surface science, SFG spectroscopy, catalysis, and electrochemical investigations on model systems, including single crystals, thin films, and deposited metal nanoparticles, under well-controlled conditions of gas composition, pressure, temperature, and potential. The UHV chamber enables us to prepare the model catalysts and to analyze their surface structure and composition by low energy electron diffraction and Auger electron spectroscopy, respectively. Thereafter, a sample transfer mechanism moves samples under UHV to the spectroscopic cell, avoiding air exposure. In the catalytic cell, SFG spectroscopy and catalytic tests (reactant/product analysis by mass spectrometry or gas chromatography) are performed simultaneously. A dedicated sample manipulation stage allows the model catalysts to be examined from LN2 temperature to 1273 K, with gaseous reactants in a pressure range from UHV to atmospheric. For post-reaction analysis, the SFG cell is rapidly evacuated and samples are transferred back to the UHV chamber. The capabilities of this new setup are demonstrated by benchmark results of CO adsorption on Pt and Pd(111) single crystal surfaces and of CO adsorption and oxidation on a ZrO2 supported Pt nanoparticle model catalyst grown by atomic layer deposition.
Highlights
Most of these early attempts were unable to spectroscopically monitor the sample during the catalytic reaction at high-pressure
A new custom-designed ultrahigh vacuum (UHV) chamber coupled to a UHV and atmosphericpressure-compatible spectroscopic and catalytic reaction cell is described, which allows us to perform IR-vis sum frequency generation (SFG) vibrational spectroscopy during catalytic measurements
Afterwards, different variants were built, with high pressure cells attached a)guenther.rupprechter@tuwien.ac.at and christoph.rameshan@tuwien.ac.at outside of a UHV chamber, enabling pre- and post-reaction analysis.11,14,15. This was a drawback since the active state of a catalyst material under reaction conditions may be different from the state determined by post reaction analysis
Summary
Most of these early attempts were unable to spectroscopically monitor the sample during the catalytic reaction at high-pressure. This was a drawback since the active state of a catalyst material under reaction conditions may be different from the state determined by post reaction analysis.. Based on the experience in designing UHV systems coupled to high pressure cells enabling simultaneous reactivity and spectroscopic measurements, we have recently designed and commissioned a new setup. Single- or polycrystalline samples are prepared and analyzed in UHV by standard methods of surface science, whereas SFG and reactivity studies [Mass Spectroscopy (MS) and Gas Chromatography (GC)] are simultaneously performed in a cell of approximately 1.5 l volume, from UHV to ambient pressure and from LN2 temperature to 1273 K. For supported Pt nanoparticles, the CO oxidation reaction was monitored, with catalytic testing being performed by MS
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