Electron spin resonance investigation of ZrO2-supported ruthenium. Evidence of strong metal–support interaction

Abstract

An e.s.r investigation of Ru/ZrO₂ has shown that Ru centres are present in different oxidation states, two of which are paramagnetic: Ru^III and Ru^I. The assignment of the electronic configuration follows from the results of the interaction of Ru/ZrO₂ with CO, for the identification of Ru^III and Ru^I, and with NO for the identification of Ru^II. Magnetic tensor components allow recognition of an Ru^III–CO adduct (g_∥= 2.039, g_⊥= 2.003) and an Ru^I–CO adduct (g= 2.05) An Ru^II–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.