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 68 3 K. For Pt, dominant sites for linear GO were in short terraces akin to th ose in high index planes. For Re, initial adsorption on three-dimensional c rystallites 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 fo rmation of Re(CO)(3) was promoted by higher precalcination temperature befo re catalyst reduction. For Pt-Re, all the effects characteristic of the sep arate 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 conta in Re atoms, which were located at kink or edge sites on the particles or w ere spread in a phase consisting mainly of Re over the alumina surface. Cok ing 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 2 93 K showing GO-induced mobility of the carbonaceous layer. (C) 1999 Elsevi er Science B.V. All rights reserved.