A convenient setup for laser-induced fluorescence imaging of both CO and CO2 during catalytic CO oxidation

We have combined three techniques, High Energy Surface X-Ray Diffraction (HESXRD), Surface Optical Reflectance, and Planar Laser Induced Fluorescence in an operando study of CO oxidation over a Pd(100) catalyst. We show that these techniques provide useful new insights such as the ability to verify that the finite region being probed by techniques such as HESXRD is representative of the sample surface as a whole. The combination is also suitable to determine when changes in gas composition or surface structure and/or morphology occur and to subsequently correlate them with high temporal resolution. In the study, we confirm previous results which show that the Pd(100) surface reaches high activity before an oxide can be detected. Furthermore, we show that the single crystal catalyst surface does not behave homogeneously, which we attribute to the surface being exposed to inhomogeneous gas conditions in mass transfer limited scenarios.

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“…More details regarding the gas system, optical access capabilities, and possible geometries of the high-pressure part are presented in Ref. 30.…”

Section: Methodsmentioning

confidence: 99%

Combining high-energy X-ray diffraction with Surface Optical Reflectance and Planar Laser Induced Fluorescence for operando catalyst surface characterization

Pfaff

Zhou

Hejral

et al. 2019

Review of Scientific Instruments

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“…We have used PLIF − to visualize the concentration or the distribution of gas phase CO and CO 2 above two different Pd single crystals. Two different laser systems and reactors were used for probing CO and CO 2 , but the layout of the experimental setup was the same in both experiments .…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Our contribution in this rapid development has been in the development of High-Energy Surface X-ray Diffraction at ultrahigh X-ray energies (HESXRD) − and of Planar Laser-Induced Fluorescence (PLIF) − applied to catalysis, providing new experimental approaches for in situ measurements.…”

Section: Introductionmentioning

confidence: 99%

Novel in Situ Techniques for Studies of Model Catalysts

et al. 2017

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Motivated mainly by catalysis, gas-surface interaction between single crystal surfaces and molecules has been studied for decades. Most of these studies have been performed in well-controlled environments and have been instrumental for the present day understanding of catalysis, providing information on surface structures, adsorption sites, and adsorption and desorption energies relevant for catalysis. However, the approach has been criticized for being too far from a catalyst operating under industrial conditions at high temperatures and pressures. To this end, a significant amount of effort over the years has been used to develop methods to investigate catalysts at more realistic conditions under operating conditions. One result from this effort is a vivid and sometimes heated discussion concerning the active phase for the seemingly simple CO oxidation reaction over the Pt-group metals in the literature. In recent years, we have explored the possibilities to perform experiments at conditions closer to those of a technical catalyst, in particular at increased pressures and temperatures. In this contribution, results from catalytic CO oxidation over a Pd(100) single crystal surface using Near Ambient Pressure X-ray Photo emission Spectroscopy (NAPXPS), Planar Laser-Induced Fluorescence (PLIF), and High Energy Surface X-ray Diffraction (HESXRD) are presented, and the strengths and weaknesses of the experimental techniques are discussed. Armed with structural knowledge from ultrahigh vacuum experiments, the presence of adsorbed molecules and gas-phase induced surface structures can be identified and related to changes in the reactivity or to reaction induced gas-flow limitations. In particular, the application of PLIF to catalysis allows one to visualize how the catalyst itself changes the gas composition close to the model catalyst surface upon ignition, and relate this to the observed surface structures. The effect obscures a straightforward relation between the active phase and the activity, since in the case of CO oxidation, the gas-phase close to the model catalyst surface is shown to be significantly more oxidizing than far away from the catalyst. We show that surface structural knowledge from UHV experiments and the composition of the gas phase close to the catalyst surface are crucial to understand structure-function relationships at semirealistic conditions. In the particular case of Pd, we argue that the surface structure of the PdO(101) has a significant influence on the activity, due to the presence of Coordinatively Unsaturated Sites (CUS) Pd atoms, similar to undercoordinated Ru and Ir atoms found for RuO(110) and IrO(110), respectively.

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“…The experimental setup and detection scheme for the CO 2 PLIF have been described in detail previously. , The detection of CO 2 was realized by exciting the (00°0) → (10°1) combination band at ∼2.7 μm and collecting the fluorescence from the fundamental band at ∼4.3 μm. The fundamental 1064 nm laser beam with ∼350 mJ/pulse from an injection seeded single-mode Nd:YAG laser was used to pump a broad-band infrared optical parametric oscillator (IR OPO; GWU, versaScan-L 1064), generating a signal beam at ∼1.7 μm and an idler beam at ∼2.7 μm, with ∼8 and ∼7 mJ/pulse, respectively, both operating at 10 Hz.…”

Section: Methodsmentioning

confidence: 99%

Simultaneous Imaging of Gas Phase over and Surface Reflectance of a Pd(100) Single Crystal during CO Oxidation

et al. 2017

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A direct correlation between the reaction activity and the surface structure of a catalyst is generally needed to better understand the mechanisms behind the heterogeneous catalysis process. In this work, we employed planar laser-induced fluorescence (PLIF) to spatially resolve the CO 2 distribution just above a Pd(100) surface, and simultaneously monitored the optical reflectance of the surface, during CO oxidation. We show that when the reaction is in the mass transfer limited regime, the inhomogeneity of the gas composition over the sample can lead to an inhomogeneity of the surface reflectance change arising from oxide formation and surface roughening. The combination of PLIF and surface reflectance also makes it possible to spatially resolve and simultaneously follow the dynamics of the gas phase and the surface on a subsecond time scale during self-sustained reaction oscillations of a Pd(100) surface, providing insights into the gas−surface interaction.

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A convenient setup for laser-induced fluorescence imaging of both CO and CO2 during catalytic CO oxidation

Cited by 23 publications

References 36 publications

Combining high-energy X-ray diffraction with Surface Optical Reflectance and Planar Laser Induced Fluorescence for operando catalyst surface characterization

Combining high-energy X-ray diffraction with Surface Optical Reflectance and Planar Laser Induced Fluorescence for operando catalyst surface characterization

Novel in Situ Techniques for Studies of Model Catalysts

Simultaneous Imaging of Gas Phase over and Surface Reflectance of a Pd(100) Single Crystal during CO Oxidation

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