Demonstrating Pressure Jumping as a Tool to Address the Pressure Gap in High Pressure Photoelectron Spectroscopy of CO and CO₂ Hydrogenation on Rh(211)

Abstract

Operando probing by x‐ray photoelectron spectroscopy (XPS) of certain hydrogenation reactions are often limited by the scattering of photoelectrons in the gas phase. This work describes a method designed to partially circumvent this so called pressure gap. By performing a rapid switch from a high pressure (where acquisition is impossible) to a lower pressure we can for a short while probe a “remnant” of the high pressure surface as well as the time dynamics during the re‐equilibration to the new pressure. This methodology is demonstrated using the CO2 and the CO hydrogenation reaction over Rh(211). In the CO2 hydrogenation reaction, the remnant surface of a 2 bar pressure shows an adsorbate distribution which favors chemisorbed CHx adsorbates over chemisorbed CO. This contrasts against previous static operando spectra acquired at lower pressures. Furthermore, the pressure jumping method yields a faster acquisition and more detailed spectra than static operando measurements above 1 bar. In the CO hydrogenation reaction, we observe that CHx accumulated faster during the 275 mbar low pressure regime, and different hypotheses are presented regarding this observation.

Microkinetic Model Fitted with a Genetic Algorithm to Experimental XPS Coverages at High Pressure–CO Hydrogenation on Rh(111)

“…The induced defect density may be particularly high under operating conditions with strongly interacting molecules, such as CO. Although not the case here at 150 mbar pressure, it has been observed previously 20 that at a higher pressure of 2 bar undercoordinated adatoms may move from the lattice onto the surface. Furthermore, the presence of step sites and point defects has been shown to destabilize CO on Rh, 46 in accordance with the prediction of the GA.…”

“…Traditionally, this has only been possible at low pressures, but with a recent setup from Amann and co-workers, measurements can be performed at pressures around 1 bar, which is close or closer to realistic reaction conditions. This high-pressure setup has been applied to investigate, e.g., CO hydrogenation on Ni, carbide formation in Fischer–Tropsch synthesis on Fe(110), CO and CO 2 hydrogenation on stepped Rh(211), the Haber-Bosch process, and methanol synthesis over Zn/ZnO/Cu(211) . Here, we focus on measurements of coverages of oxygen- and carbon-containing species on Rh(111) during CO hydrogenation at 150 mbar and temperatures from 175 to 325 °C .…”

Effect of CO2-Rich Syngas on the Chemical State of Fe(110) during Fischer–Tropsch Synthesis

“…32 We have observed, at several occasions in previous experiments on other transition metal catalysts that the hydrogen pressure for CO 2 and CO hydrogenation reactions in particular is required to be in the proximity of 100 mbar in order for an effective hydrogenation of the surface species to occur, and the rate of this hydrogenation is very dependent on the partial pressure of H 2 . 13,14,16,47 The dependency of the H 2 pressure is furthermore the reason for the immense growth of surface carbon adsorbates around 284.6 eV in the C 1s region of Figure 3; with the low hydrogen partial pressure below 80 mbar, the adsorbates accumulate on the surface rather than being terminated by hydrogen and desorbed.…”