Metal-support interactions in cobalt-aluminum co-precipitated catalysts: XPS and CO adsorption studies

Cobalt-aluminum catalysts were prepared using either the precipitation of C o2+ in the presence of freshly prepared Zn-Al hydrotalcite (the promoted sa mple) or the co-precipitation of Co2+ and Al3+ (the unpromoted samples). Th e evolution of the initial hydrotalcite-like structure was monitored during its calcination and the reductive treatment by means of XPS. It was shown that at 480 degreesC the reduction of the calcined samples results in the f ormation of Co-0 species, the further reduction at 650 degreesC results in an increase of the amount of the Coo species. The samples reduced at 650 de greesC chemisorb readily carbon monoxide at 77 K, while the sample reduced at 480 degreesC does not chemisorb CO at 77 K. At elevated temperatures, al l reduced samples are found to be able to chemisorb Co-0. Terminal CO moiet ies as well as monodentate carbonates, formates and carboxyl species were d etected at the surface of the reduced samples at their exposure to the CO m edium at the elevated temperature. The intensity of the IR absorption bands of chemisorbed CO are found proportional to the surface fraction of the Co -0 species, measured by XPS. The apparent red shift of the IR absorption ba nds is observed for CO adsorbed on the samples reduced at 480 degreesC. The obtained data correlate with the catalytic properties of the Co-Al samples in hydrogenation reactions. The conclusion on the existence of a strong me tal-support interaction in the samples under the study is made. (C) 2001 El sevier Science B.V. All rights reserved.