Electron Paramagnetic Resonance investigation of the nature of active species involved in carbon black oxidation on ZrO2 and Cu/ZrO2 catalysts

To identify the nature of active paramagnetic species involved in the carbon black (CB) oxidation, an Electron Paramagnetic Resonance (EPR) study of (CB-ZrO2) and (CB-Cu/ZrO2) loose contact mixtures treated under argon flow has been undertaken. In the presence of pure zirconia catalysts, it was found that ZrO2 interacts with CB and can be reduced into Zr3+ formed in tetragonal phase of this oxide support. In parallel, several EPR signals assigned to carbonaceous radicals were detected: i) carbonaceous radicals on CB surface, ii) radicals located at the CB-ZrO2 interface and iii) oxygen deficit carbonaceous radicals observed at high treatment temperature. The carbonaceous signals disappeared completely after CB oxidation in agreement with a regeneration of the catalyst treated under air. For copper supported on zirconia catalysts, oxygen surrounding isolated Cu(II) species and oxygen from tetragonal ZrO2 lattice are involved in carbon black oxidation. The phenomenon is reversible and this catalyst is also regenerated by air. Carbonaceous radical signals were also observed for (CB-Cu/ZrO2) mixture and their intensity decrease versus temperature appeared in good agreement with the better activity of Cu/ZrO2 compared to pure ZrO2. (C) 2011 Elsevier B.V. All rights reserved.