Previous work showed that calcination in O-2 of physical mixtures of Fe2O3 and supported Pt leads to a strong reduction enhancement of the Fe2O3, but that a much smaller effect was observed with supported Pd. The present results show that a strong reduction enhancement could be achieved by pretreating Pt/Al2O3 or Pd/Al2O3 with NH4Cl and then decomposing NH4Cl, before mixing the solid with Fe2O3. Such pretreatment with NH4Cl has no effect on SiO2 or zeolite-supported metals, because only Al2O3 retains chloride ions at its surface. In the physical mixtures, chlorides migrate from Al2O3 to Fe2O3 at elevated temperature and form a volatile compound, presumably FeCl3. Layered-bed experiments show that this FeCl3 sublimes, and that its chemical interaction with Pt or Pd on any support results in the formation of mobile Pt- or Pd-chloro complexes that reach Fe2O3 particles by surface migration. After exposure to an H-2 flow, the complexes are reduced, and Pt or Pd particles are formed on the Fe2O3, enhancing its reduction by H spillover. These metal particles on the Fe2O3 have been identified by TEM and X-ray energy dispersive spectroscopy (EDS). Abundant formation of PdFe alloys upon reduction is verified by TPR/TPD, indicating that almost all Pd has interacted with the volatile Fe chloride. In the absence of a transition metal, chloride ions retard the reduction of Fe2O3.