Platinum migration out of zeolites onto iron oxide: an alternative to H spillover

TPR shows that the reduction of Fe2O3 to Fe3O4 is strongly enhanced in mixtures with platinum-containing mordenite. However, no hydrogen spillover takes place from Pt-0 particles along the walls of the zeolite pores. Only migration of platinum out of the zeolite onto the Fe2O3 leads to enhanced reduction of Fe2O3. TEM and EDX prove unambiguously that Pt clusters decorate Fe2O3 particles after an oxidative pretreatment of intimate mixtures, followed by reduction. Two paths exist for this migration of oxidized platinum: as Pt2+ ions and as PtO or PtO2 clusters. The rate for both transport mechanisms increases with temperature. Pretreatment with H2O vapor results in hydrated ions which have higher mobility and lead to more homogeneous distribution of the platinum over iron oxide particles. Reduction in wet hydrogen is slower than in dry hydrogen; no reduction to Fe-0 occurs in wet hydrogen.