The formation of carbon surface oxygen complexes by oxygen and ozone. The effect of transition metal oxides

Various surface oxygen complexes (SOCs) have been identified by DRIFT spectroscopy on the surface of carbon black (Printex-U) after partial non-catalytic conversion in 10% O-2 in Ar and ozone. An in situ DRIFT analysis of the oxidation of fullerene C-60 showed the formation of similar functionalities and validated the use of C-60 as a carbon black model compound for DRIFT spectroscopic studies, although C-60 is more reactive towards oxygen than carbon black. Ex situ DRIFT analyses of partially converted catalyst/carbon black mixtures and in situ analyses of catalytic fullerene C-60 oxidation, revealed that several transition metal oxides (Cr2O3, MoO3, V2O5 and CuO) promote the formation of SOCs. Fe2O3 and Co3O4 do not enhance the formation of SOCs in 10% O-2 in Ar and prevent the formation of SOCs on carbon black samples in ozone. Reaction of carbon black with oxygen associated with metal oxides (carbothermic reduction) does not yield SOCs. Apparently, lattice oxygen is not directly involved in the catalytic formation of these complexes. Indications for chemical interactions between metal oxides and either carbon black or C-60, such as M-O-C bonds, have not been found. Spill-over of activated oxygen from the Cr2O3, MoO3, V2O5 and CuO surfaces onto the carbon black surface is likely to explain the catalytic formation of SOCs. (C) 1998 Elsevier Science Ltd. All rights reserved.