Interaction between Pt and MoO3 dispersed over alumina

Pt-xMo/gamma-Al2O3 catalysts of different molybdenum loading (2-20 wt.%) an d with 1 wt.% of platinum were prepared by successive wet impregnation afte r intermediate calcination. The structure, morphology and surface were char acterized by various methods.:The DRS results indicate the presence of octa hedral Mo6+ and tetrahedral Mo6+ phases. It also evidences the presence of polymeric MoOx species, responsible for the formation of a well dispersed s urface sublayer and bulk MoO3 crystalline phase. XPS results after reductio n and passivation of the 1Pt and 1Pt2Mo revealed the presence of residual c hlorine, in the form of surface species such as [Pt(OH)(x)Cl-y](s) and [PtO xCly](s)favoring the formation of well dispersed platinum particles. The TP D and FTIR results are consistent with the existence of new active sites of Pt in the presence of molybdenum loading. For low Mo content there is a H- 2 spillover effect. These results confirm the decoration model of Pt encaps ulation by partially reduced Mo species as well as H-2 Storage and backspil lover due to the generation of a: bronze compound. (C) 2000 Elsevier Scienc e B.V. All rights reserved.