Title

Chemisorption of CO on the Ir(111) Surface: Adsorption And Desorption Kinetics Measured With in Situ Vibrational Spectroscopy

Document Type

Article

Subject Area(s)

Engineering, Chemical Engineering, Catalysis and Reaction Engineering, Membrane Science, Physics, Condensed Matter Physics

Abstract

The kinetics of adsorption and desorption of carbon monoxide on Ir(111) have been investigated using the well-defined and carefully calibrated IR absorption peak position of the CO intramolecular stretching vibration as a nonintrusive coverage probe. Experiments were performed with time-resolved Fourier transform infrared reflection–absorption spectroscopy (TR-IRAS), which allows high-resolution measurements over a large pressure range between 1×10−8" role="presentation" style="box-sizing: border-box; display: inline; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; color: rgb(51, 51, 51); font-family: Arial, sans-serif; position: relative;">1×10−81×10−8 and 1×10−5 mbar" role="presentation" style="box-sizing: border-box; display: inline; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; color: rgb(51, 51, 51); font-family: Arial, sans-serif; position: relative;">1×10−5 mbar1×10−5 mbar and surface temperature range between 390 and 500 K. The rate of desorption into vacuum is compared with the rate of desorption in the presence of a finite pressure of the desorbing gas. In this case, a flux-dependent enhancement of the desorption rate has been observed previously, which, if existent, should have an important impact on heterogeneously catalyzed reactions performed under high-pressure conditions. Most of these experiments, however, were performed using thermal desorptionspectroscopy, a nonequilibrium method. We have been able to measure all rate parameters that are essential to describe the desorptionin situ with TR-IRAS and have, thereby, clarified the disagreements that exist in the literature.