Interaction between Pt and MoO3 dispersed over alumina

Pt-xMo/γ-Al2O3 catalysts of different molybdenum loading (2-20 wt.%) and with 1 wt.% of platinum were prepared by successive wet impregnation after intermediate calcination. The structure, morphology and surface were characterized by various methods. The DRS results indicate the presence of octahedral Mo6+ and tetrahedral Mo6+ phases. It also evidences the presence of polymeric MoOx species, responsible for the formation of a well dispersed surface sublayer and bulk MoO3 crystalline phase. XPS results after reduction and passivation of the 1Pt and 1Pt2Mo revealed the presence of residual chlorine, in the form of surface species such as [Pt(OH)xCly]s and [PtOxCly]s favoring the formation of well dispersed platinum particles. The TPD 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 H2 spillover effect. These results confirm the decoration model of Pt encapsulation by partially reduced Mo species as well as H2 storage and backspillover due to the generation of a bronze compound.