Carbon monoxide and oxygen interaction with Ru/MgF2 catalyst: IR and EPR studies

摘要

Electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy were used to study the formation of ruthenium and adsorbed species appearing on the catalyst upon the adsorption of CO and O2 on 1.37 wt% Ru/MgF2 catalysts derived from Ru3(CO)12. The presence of Ru x+ sites in spite of a reductive H2 treatment at 673 K was observed by EPR and IR spectroscopy beside metallic Ru0 species. Both IR and EPR results provided clear evidence for the interaction between surface ruthenium and probe molecules. The IR spectra recorded after admission of CO showed a band at approx. 2000 cm?1, due to linearly adsorbed CO on Ru0/MgF2 and two bands at higher frequencies (approx. 2140 and approx. 2070 cm?1), related to CO on oxidized Ru n+ species, e.g., to Ru(CO)3 complex with Ru in the 1+ and/or 2+ state of oxidation and Ru(CO)2 with Ru in the 3+ and/or 4+ state of oxidation. A weak anisotropic EPR signal with g ‖ = 2.017 and g ⊥ = 2.003 is due to O 2 ? radicals and a formation of Ru4+-O 2 ? complex is postulated. The Ru3+ appears to oxidize to Ru4+ and the resulting dioxygen anion is coordinated to the ruthenium. The strong, isotropic EPR signal at g 0 = 2.003 detected upon admission of CO is attributed to CO radical anion rather than to any ruthenium carbonyl complexes.