Chemisorption of Nitric Oxide on Char. 2. Irreversible Carbon Oxide Formation

The process of chemisorption of nitric oxide (NO) on a carbon derived from phenol-formaldehyde resin has been studied at temperatures between 323 and 473 K, and at NO partial pressures between 2.02 and 10.1 kPa. The process of chemisorption can be split into two separate pathways: one a reversible chemisorptive pathway forming nitric oxide surface complexes C(NO) and the other an irreversible chemisorptive pathway yielding N₂ and carbon surface oxides C(O) and C(O2). The processes of formation of the surface oxides both appear to involve dual-site mechanisms, and all these processes are kinetically second order with respect to NO. The latter has been hypothesized to be a consequence of the tendency of NO to form a dimer species within microporous carbons. Within the temperature range studied, the irreversible chemisorptive processes can only be studied on a surface that has been first cleaned by desorption of oxides. There are particular sites created by surface cleaning that, once filled, are not regenerated. The irreversible processes that form the surface oxides have an extremely low activation energy barrier.