Pressure Jumping as a Tool to Circumvent the Pressure Gap in High-Pressure X-ray Photoelectron Spectroscopy, Demonstrated Using CO and CO2 hydrogenation on Rh(211)

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. The time dynamics during the re-equilibration to the new pressure may also be studied. This methodology is demonstrated using the CO2 the CO hydrogenation reaction over Rh(211). In the CO2 hydrogenation reaction, the remnant surface of a 2 bar pressure shows a higher degree of CHx adsorbates and less chemisorbed CO compared to static operando spectra acquired at lower pressures. Hydrogenated CO2 shows as intermediates during the re-equilibration period. In the CO hydrogenation reaction, we observe that CHx accumulated faster during the 275 mbar low pressure regime, indicating that the termination of hydrocarbons is the most affected part of the reaction mechanism by the ~1100 mbar pressure gap.