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

The mechanism of the reaction of NO with ashless carbon black was studied in detail. The differences between the amounts of oxygen and nitrogen measured and the calculated concentrations of oxygen and nitrogen suggest the formation of surface carbon-oxygen complexes C(O) and carbon-nitrogen complexes C(N). The dependence of the specific rate of reaction at its initial stage on temperature is different from that at steady state, pointing to different rate-determining steps for the two reaction regimes. The decomposition of surface complexes is suggested to be the rate-determining step for the reaction 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 dissociation of the N-O bond leads to the formation of C(O) and C(N) complexes which are heterogeneous in structure. The adsorbed NO molecules are not stable on the carbon black surface at temperatures above 300 degrees C. The reaction of NO with carbon at higher temperatures results in the formation of more surface complexes with higher thermal stability. The surface C(O) complexes involved in the CO formation differ in structure from those involved in the CO2 formation. The mechanism of the NO-carbon reaction at low temperatures appears to be different from that at high temperatures (>750 degrees C). (C) 2000 Elsevier Science Ltd. All rights reserved.