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

Abstract

Abstract To identify the nature of active paramagnetic species involved in the carbon black (CB) oxidation, an Electron Paramagnetic Resonance (EPR) study of (CB–ZrO 2 ) and (CB–Cu/ZrO 2 ) loose contact mixtures treated under argon flow has been undertaken. In the presence of pure zirconia catalysts, it was found that ZrO 2 interacts with CB and can be reduced into Zr 3+ 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–ZrO 2 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 ZrO 2 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/ZrO 2 ) mixture and their intensity decrease versus temperature appeared in good agreement with the better activity of Cu/ZrO 2 compared to pure ZrO 2 .