ELECTRON-SPIN RESONANCE INVESTIGATION OF ZRO2-SUPPORTED RUTHENIUM - EVIDENCE OF STRONG METAL-SUPPORT INTERACTION

An e.s.r investigation of Ru/ZrO2 has shown that Ru centres are present in different oxidation states, two of which are paramagnetic: RuIII and RuI. The assignment of the electronic configuration follows from the results of the interaction of Ru/ZrO2 with CO, for the identification of RuIII and RuI, and with NO for the identification of RuII. Magnetic tensor components allow recognition of an RuIII-CO adduct (g∥ = 2.039, g⊥ = 2.003) and an RuI-CO adduct (g = 2.05) An RuII-NO species was also identified [g⊥ = 2.00, g∥ = 1.91, A⊥ (N) = 40 G]. The results of the interaction with O2 also have been discussed in order to give a fuller description of the electronic configuration of the surface ruthenium centres and of the interaction effects between metal and support centres. It appears that at the Ru-ZrO2 interface occurs an interaction stronger than in the Ru-γ-Al2O3 case, the strength depending also on the temperature of the pyrolysis used to obtain Ru/ZrO2 from the Ru3(CO)12/ZrO2 metal precursor. Also the analogous Rh/ZrO2 system was considered with respect to interaction with NO in order to compare the variation in the metal-support interaction owing to differences in the supported metal.