Existence de quatre types de sites reactionnels dans l'oxydation du graphite

We have studied the temperature programmed decomposition of graphite-oxygen surface complexes using a gas flow apparatus under atmospheric pressure with infrared CO and CO₂ detection. We have shown that the oxygen is chemisorbed on four types of sites forming surface complexes which on decomposition give mainly CO and some CO₂. The first two types of sites, A and B, are formed by ‘labile’ carbon atoms created during the degassing carried out prior to each experiment. These two types of sites disappear without reconstitution upon desorption of the complexes. The other two, C and D, are formed by edge carbon atoms, normally linked to other atoms in the graphite lattice. The C type sites form by oxidation only at temperatures below about 950°C and give rise to hexagonal pits with sides oriented in the (101?0) crystallographic direction (‘arm-chair’ configuration). The D type sites form at temperatures above about 950°C and give rise to hexagonal pits oriented in the (11?20) crystallographic direction (‘zig-zag’ configuration). Water inhibits the formation of oxygen surface complexes on the C sites and it may be considered that it is essentially on these sites that the water is chemisorbed.