Evidence of strong metal-support interaction in alumina-supported platinum catalysts

Abstract

Using temperature-programmed reduction (TPR) technique, combined with TEM and n-heptane conversion, an investigation on the metal-support interaction has been made for reduced and reoxidized alumina-supported platinum (1 wt%) catalysts. It has been found that during reduction the metal combines intimately with the support, and the formation of a Pt-Al alloy is proposed. As the reduction temperature increases so as to facilitate the reduction of alumina, the metal-support interaction is strengthened through the transformation of the platinum-rich alloy to an alumina-rich one on the surface, and a diffusion of some of the platinum atoms into the support sub-layers. Reoxidation is shown to cause a segregation of the alloys as a result of the weakening of metal-support interactions. Thus, a platinum-rich alloy can be formed for the reoxidized samples during their subsequent reduction at mild temperatures, which leads to the changes in the chemisorption and catalytic properties, as observed in the catalysts originally reduced at high temperatures.