IR study of CO adsorption on Pt, Re and Pt-Re/Al2O3 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 GO were in short terraces akin to those in high index planes. For Re, initial adsorption on three-dimensional crystallites giving Re-O-CO was followed by slow carbonylation leading to Re-2(CO)(10), Re(CO)(3) and possibly Re(CO)(5) on the alumina support. The formation of Re(CO)(3) was 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 Be, although the latter was enhanced for Pt-Re. Small patches of uncoked Pt were enlarged after addition of CO at 293 K showing GO-induced mobility of the carbonaceous layer. (C) 1999 Elsevier Science B.V. All rights reserved.