Strong metal-support interactions: Occurrence among the binary oxides of groups IIA?VB

Iridium, supported on a number of oxides from Groups IIA, IIIB, IVB, and VB, exhibits normal H2-chemisorption (typical of IrAl2O3 and IrSiO2) following reduction at 200 °C. If supported on MgO, Sc2O3, Y2O3, ZrO2, or HfO2, this behavior is not seriously affected by reduction temperatures ⩽ 700 °C. If, however, the carrier is TiO2, V2O3, or Nb2O5 HM is decreased to near-zero by reduction at 500 °C, while Ta2O5 requires 700 °C for this. This strong metal-support interaction is discussed in terms of the need for a reducible, transition metal oxide support and on the basis of bonding mechanisms suggested by known compounds.