Reaction of NO with carbonaceous materials - 1. Reaction and adsorption ofNO on ashless carbon black

The mechanism of the reaction of NO with ashless carbon black was studied i n detail. The differences between the amounts of oxygen and nitrogen measur ed and the calculated concentrations of oxygen and nitrogen suggest the for mation of surface carbon-oxygen complexes C(O) and carbon-nitrogen complexe s C(N). The dependence of the specific rate of reaction at its initial stag e on temperature is different from that at steady state, pointing to differ ent rate-determining steps for the two reaction regimes. The decomposition of surface complexes is suggested to be the rate-determining step for the r eaction under steady-state conditions. This explains very well the measured zero reaction order with respect to NO. NO is proposed to adsorb parallel to the carbon black surface. The dissocia tion of the N-O bond leads to the formation of C(O) and C(N) complexes whic h are heterogeneous in structure. The adsorbed NO molecules are not stable on the carbon black surface at temperatures above 300 degrees C. The reacti on of NO with carbon at higher temperatures results in the formation of mor e surface complexes with higher thermal stability. The surface C(O) complex es involved in the CO formation differ in structure from those involved in the CO2 formation. The mechanism of the NO-carbon reaction at low temperatu res appears to be different from that at high temperatures (>750 degrees C) . (C) 2000 Elsevier Science Ltd. All rights reserved.