Demonstrating Pressure Jumping as a Tool to Address the Pressure Gap in High Pressure Photoelectron Spectroscopy of CO and CO 2 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 as well as the time dynamics during the re-equilibration to the new pressure. This methodology is demonstrated using the CO and the CO hydrogenation reaction over Rh(211). In the CO hydrogenation reaction, the remnant surface of a 2 bar pressure shows an adsorbate distribution which favors chemisorbed CH 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 CH accumulated faster during the 275 mbar low pressure regime, and different hypotheses are presented regarding this observation.