Atmospheric pressure reaction cell for operando sum frequency generation spectroscopy of ultrahigh vacuum grown model catalysts

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 LN 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 ZrO supported Pt nanoparticle model catalyst grown by atomic layer deposition.

Coverage-Induced Orientation Change: CO on Ir(111) Monitored by Polarization-Dependent Sum Frequency Generation Spectroscopy and Density Functional Theory

“…The experimental setup has been described in detail previously. 11 Briefly, SFG measurements were performed using a 20 ps mode-locked Nd:YAG laser system (EKSPLA, PL2241) with a fundamental radiation of 1064 nm (30 mJ/pulse, 50 Hz repetition rate). A part of the fundamental radiation is frequency-doubled to 532 nm, one part of which is used as the visible input for the SFG process, and another one pumps an optical parametric system.…”

“…The temperature was measured by a nickel/chromel thermocouple. The sample could be resistively heated to 1273 K and cooled with liquid nitrogen to 95 K. 11 Ir(111) was prepared by repeated cycles of sputtering with Ar + ions (beam energy 1.2 keV at 5 × 10 –6 mbar Ar, 30 min), oxidizing (1 × 10 –7 mbar O 2 , 4 min) at 850 K, and UHV annealing at 1050 K for 1 min. This procedure leads to clean surfaces, as confirmed by X-ray photoelectron spectroscopy (XPS) and described in detail in ref ( 36 ).…”

“…Using a sample transfer rod, the single crystal can be moved in UHV to an attached SFG cell, which allows performing experiments from UHV to 1 bar and at 95–773 K (for details see ref ( 11 )). In order to guarantee a clean Ir(111) surface during transfer to the SFG cell, 1 × 10 –7 mbar CO was typically introduced to the UHV chamber (10 min), to saturate/passivate the Ir surface at room temperature.…”

Polarization-Dependent SFG Spectroscopy of Near Ambient Pressure CO Adsorption on Pt(111) and Pd(111) Revisited

“…The experiments on Pt(111) and Pd(111) single crystals were performed in a new UHV surface analysis system equipped with an SFG-compatible UHV-high pressure cell [ 25 ] (setup similar to that described in Refs. [ 2 , 29 ]).…”

“…This is due to the complexity of the orientation analysis, which is based on polarization-dependent SFG spectroscopy, and the analysis/modeling of the observed intensities (which sometimes includes simplifications and/or assumptions that may not be justified). In this contribution, we revisit the benchmark systems of CO/Pt(111) and CO/Pd(111), employing a new SFG setup (UHV to mbar) [ 25 ] and specifically discuss the orientation analysis in detail, also reflecting analogies and differences to previous studies.…”