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

The effect of H-2 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 H-2. Results at room temperature showed less linearly adsorbed CO on the H-2-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 H-2-preadsorbed surface, in marked contrast, generated a narrower band, representing a more uniform set of Co CO coordination sites. This indicates that H-2 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 degrees C, however, were found to be opposite, that is, much more adsorbed CO was found over a H-2-preadsorbed surface than the bare surface, suggesting that the catalyst surface is modified by H-2 at higher temperatures and facilitates CO adsorption. Syngas (1:1 H-2/CO) flow over bare and H-2-preadsorbed surfaces resulted in intermediate peak intensities compared to CO adsorption over either a bare surface or H-2-preadsorbed cobalt surface.