PROMOTER EFFECT OF NIOBIA ON PT AL2O3 CATALYSTS .2. EFFECT OF CHLORINE AND NB2O5 CONTENT ON THE STRUCTURE AND REACTIVITY IN CH3OH/D2 EXCHANGE/

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 b oth chlorine-containing and chlorine-free Pt samples measured by TPR. XPS provides evidence for the effect of chlorine and niobia on the red uction of Pt. After reduction Nb2O5 is converted into NbO(x) species w hich may migrate on top of the Pt particles measured by XRD, CO chemis orption and O/H titration. The increased perimeter of the Pt/NbO(x)/Al 2O3 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.