Promoter effect of niobia on Pt/Al2O3 catalysts.

Abstract

The effect of chlorine using precursors like H₂PtCl₆ (0.55,2 and 10 wt.% Pt) and Pt(NH₃)₄(NO₃)₂ (2 wt.% Pt) and of the Nb₂O₅ loading on the structure of Pt/Al₂O₃ and its catalytic activity in methanol/deuterium exchange has been investigated. In presence of niobia the BET surface of the support increases but niobia itself remains amorphous and its presence in increasing quantities results in the easier reduction of both chlorine-containing and chlorine-free Pt samples measured by TPR. XPS provides evidence for the effect of chlorine and niobia on the reduction of Pt. After reduction Nb₂O₅ is converted into NbO_x species which may migrate on top of the Pt particles measured by XRD, CO chemisorption and O/H titration. The increased perimeter of the Pt/NbO_x/Al₂O₃ interface raises the deuterium availability across this interface, which in turn, gives rise to the interaction of methyl groups in the anchored species with Pt for multiple exchange as was assumed in Part I.