IR study of CO adsorption on Pt, Re and Pt–RerAl O 2 3 catalysts before and after coking

Infrared �IR. spectra are reported of CO adsorbed on alumina-supported Pt, Re and Pt–Re catalysts before and after
coking by exposure to heptane at 683 K. For Pt, dominant sites for linear CO were in short terraces akin to those in high
index planes. For Re, initial adsorption on three-dimensional crystallites giving Re`–CO was followed by slow carbonyla-
tion leading to Re2�CO.10, Re�CO.3and possibly Re�CO.5on the alumina support. The formation of Re�CO.3was
promoted by higher precalcination temperature before catalyst reduction. For Pt–Re, all the effects characteristic of the
separate catalysts were observed. The Pt dispersions were similar for Pt alone and Pt–Re. However, the availability of Re
sites was considerable enhanced in the mixed system. Short terraces on Pt or Pt–Re particles did not contain Re atoms,
which were located at kink or edge sites on the particles or were spread in a phase consisting mainly of Re over the alumina
surface. Coking of Pt was greater than that of Re, although the latter was enhanced for Pt–Re. Small patches of uncoked Pt
were enlarged after addition of CO at 293 K showing CO-induced mobility of the carbonaceous layer.