Ambient Pressure Photoelectron Spectroscopy: Opportunities in Catalysis from Solids to Liquids and Introducing Time Resolution

Abstract

Photoelectron spectroscopy is an excellent technique to explore chemically complex systems in catalysis. However, due to a small mean free path of photoelectrons in gas, liquid, and solid media, the study of the gas–solid, liquid–gas, solid–liquid interfaces, as well as liquid homogeneous systems are a serious challenge. With differentially pumped analyzers this limitation ceases to exist and no longer restricts photoelectron spectroscopy only to ultra‐high vacuum conditions. Presently, photoemission studies at tens of mbar of pressure are possible. To reach atmospheric pressure and even higher, membrane‐covered closed cells have been developed. Graphene membranes are impermeable to molecules and almost transparent to photoelectrons. They are used as a pressure barrier between the enclosed cell at atmospheric pressure and the electron analyzer at vacuum while allowing transmission of photoelectrons. By accessing to atmospheric pressure range, with this kind of cell, photoemission studies will become a versatile in situ and operando tool for catalysis. Studies involving liquids in static conditions are an important aspect in this direction, which can be extended to homogeneous catalytic systems. Liquids are presently accessible using micro‐jets. Another aspect which is of paramount interest to investigate catalysts is time resolution. By improving the time resolution of photoemission measurements to the sub‐second regime it is possible to follow the kinetic changes that are crucial of a catalytic reaction, the changes that occur during catalyst pretreatment and activation, and notably to differentiate active species from spectator ones, which may be the dominating species in a classical experiment.

Variation of Aluminium Distribution in Small‐Sized ZSM‐5 Crystals during Desilication

“…The zeolite powder samples were dispersed in ethanol and drop‐casted as a thin film on a gold foil (Sigma–Aldrich, purity 99.99 %). The gold foil was mounted to the sample holder of the solid–gas interface endstation, which allows measurements at precise pressures with a flow conditions of gas/gas mixtures . The spectra were recorded at 80 °C and 1 mbar of helium (Messer gas, 99.999 % purity) to minimize the charging of the samples.…”

“…The gold foil was mounted to the sample holder of the solid-gas interface endstation, which allows measurements at precise pressures with af low conditions of gas/ gas mixtures. [40,41] The spectra were recorded at 80 8Ca nd 1mbar of helium (Messer gas, 99.999 %p urity) to minimize the charging of the samples. Si 2p and Al 2p photoemission spectra were recorded tuning the excitation energies between 480 to 1210 eV, such that for both elements the photoelectron kinetic energies are 400, 600, 800 and 1100 eV.A fter subtraction of aS hirley background, the spectra were fitted with Voigt shaped peaks.…”

Homogenous Meets Heterogenous and Electro‐Catalysis: Iron‐Nitrogen Molecular Complexes within Carbon Materials for Catalytic Applications

“…This has allowed the development of ambient‐pressure XPS (APXPS) instrumentations . Synchrotron‐based APXPS further allows for the modulation of the excitation wavelength, which in turn may refine the penetration depth of the probing beam . Using a combined APXPS and theoretical approach, Artyushkova et al .…”

Formation and Functioning of Bimetallic Nanocatalysts: The Power of X‐ray Probes

“…[41] Soft Xray tools favor UHV,though major progress has been made to allow gas pressures and elevated temperatures to mimic realistic conditions.F or example,t ime-resolved NAP-XPS gained prominence in operando characterization, [42] taking advantage of small dead-volume reaction cells [43] and fast delay line detectors.X RS can probe soft X-ray edges using Raman scattered hard X-rays,a llowing in situ and operando conditions. [41] Soft Xray tools favor UHV,though major progress has been made to allow gas pressures and elevated temperatures to mimic realistic conditions.F or example,t ime-resolved NAP-XPS gained prominence in operando characterization, [42] taking advantage of small dead-volume reaction cells [43] and fast delay line detectors.X RS can probe soft X-ray edges using Raman scattered hard X-rays,a llowing in situ and operando conditions.…”

“…To probe all layers of complexity in bimetallic nanocatalysts,insitu and operando characterization is essential to capture their structural and electronic properties under relevant conditions.O wing to their penetrative nature,h ard X-rays are powerful tools to monitor nanocatalysts under harsh conditions,w hich resulted in the design of dedicated high-temperature and high-pressure reaction cells. [41] Soft Xray tools favor UHV,though major progress has been made to allow gas pressures and elevated temperatures to mimic realistic conditions.F or example,t ime-resolved NAP-XPS gained prominence in operando characterization, [42] taking advantage of small dead-volume reaction cells [43] and fast delay line detectors.X RS can probe soft X-ray edges using Raman scattered hard X-rays,a llowing in situ and operando conditions.…”