Atmospheric pressure X-ray photoelectron spectroscopy apparatus: Bridging the pressure gap

Abstract

One of the main goals in catalysis is the characterization of solid/gas interfaces in a reaction environment. The electronic structure and chemical composition of surfaces become heavily influenced by the surrounding environment. However, the lack of surface sensitive techniques that are able to monitor these modifications under high pressure conditions hinders the understanding of such processes. This limitation is known throughout the community as the "pressure gap." We have developed a novel experimental setup that provides chemical information on a molecular level under atmospheric pressure and in presence of reactive gases and at elevated temperatures. This approach is based on separating the vacuum environment from the high-pressure environment by a silicon nitride grid-that contains an array of micrometer-sized holes-coated with a bilayer of graphene. Using this configuration, we have investigated the local electronic structure of catalysts by means of photoelectron spectroscopy and in presence of gases at 1 atm. The reaction products were monitored online by mass spectrometry and gas chromatography. The successful operation of this setup was demonstrated with three different examples: the oxidation/reduction reaction of iridium (noble metal) and copper (transition metal) nanoparticles and with the hydrogenation of propyne on Pd black catalyst (powder).

Combined soft and hard X-ray ambient pressure photoelectron spectroscopy studies of semiconductor/electrolyte interfaces

“…the solid or the liquid side [23,30,31]. Using supported membranes, such as graphene on a silicon nitride grid, or coated membranes, where the total thickness of the solid material is less than two to three times the mean free path of electrons, photoemission experiments can be conducted from the solid side of the solid/liquid interface (see Figure 2A) [30,31]. When combined with a flow cell, this approach has the advantage that the liquid electrolyte can flow through the system thereby providing facile mass transport in the liquid electrolyte.…”

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

“…In that case, molecules are constrained within the enclosed region by the membrane and do not flow into the analyzer; however, photoelectrons can. Measurements up to 1 atm have been already performed with this setup . The two types of measurement setups are discussed in more details below.…”

“…A cost effective fabrication of an in situ cell which uses a photoelectron transparent membrane will increase the adaptation of this technique for versatile experiments including the liquid homogeneous systems. Few groups have implemented graphene membranes for fabricating in situ cells for APXPS at or in access of one bar pressure, while many more are likely to use such cells as they will become readily available.…”

“…Presently, photoemission measurements around tens of mbar pressures are routinely possible with the commercially available differentially pumped electron analyzers. In lieu of present APXPS arrangements of a small reaction cell or a comparatively large UHV chamber, a modified setup can be designed with a photoelectron semi‐transparent membrane covered cell, which can reach atmospheric and even higher pressures without affecting the vacuum of the analyzer . This will be further discussed below.…”

UHV and Ambient Pressure XPS: Potentials for Mg, MgO, and Mg(OH)2 Surface Analysis

“…The technique allows pressures at the sample in the mbar regime, with a demonstrated maximum pressure of 130 mbar for a standard sample environment 5 and 1 bar for a graphene membrane-based one. 6 Hence, fundamental studies, such as on the hydroxylation of MgO and investigations of Mg(OH) 2 relevant to applications, can be conducted in ambient in situ and operando conditions using APXPS.…”