Effect of H₂ Preadsorption on CO Interactions with a Co/Re/Zr/SiO₂‑Based Catalyst: In Situ DRIFTS Study

The effect of H₂ preadsorption on the adsorption of CO on a 10% Co, 4% Re/(2% Zr/SiO₂) catalyst was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at different temperatures. CO adsorption experiments were carried out on a bare catalytic surface (reduced in flowing hydrogen, followed by flush with helium) and on the surface preadsorbed with H₂. Results at room temperature showed less linearly adsorbed CO on the H₂-preadsorbed surface than the bare surface. On a bare surface at room temperature, CO adsorbed producing a broad band covering a wide range of wavenumbers. CO adsorption over a H₂-preadsorbed surface, in marked contrast, generated a narrower band, representing a more uniform set of Co–CO coordination sites. This indicates that H₂ precoordination at room temperature blocks a number of different cobalt coordination sites, which allows CO coordination to a more electronically uniform set of cobalt sites. The results at temperatures from 230 to 300 °C, however, were found to be opposite, that is, much more adsorbed CO was found over a H₂-preadsorbed surface than the bare surface, suggesting that the catalyst surface is modified by H₂ at higher temperatures and facilitates CO adsorption. Syngas (1:1 H₂/CO) flow over bare and H₂-preadsorbed surfaces resulted in intermediate peak intensities compared to CO adsorption over either a bare surface or H₂-preadsorbed cobalt surface.