The literature on the kinetics of the NO-carbon reaction is reviewed.
Data are examined both from studies in which catalysis played no role
and from studies in which catalysts were present as a result of additi
on or as natural inclusions (i.e. in coals). It is concluded that ther
e generally exist three distinct reaction regimes, defined in terms of
reaction temperatures. There is a near-ambient-temperature chemisorpt
ion regime, in which steady gasification is not possible. In this regi
me, both reversible and irreversible chemisorption processes are obser
ved. A low-temperature gasification regime is observed at temperatures
above similar to 500 K, but below similar to 1000 K. A high-temperatu
re gasification regime is observed above this transition temperature.
The low-temperature gasification regime is characterized by low activa
tion energies, and the high-temperature regime by high activation ener
gies. These two distinct gasification regimes however are not observed
in all cases, and there is as yet no clear understanding of what dete
rmines this. In the reaction of pure NO with carbons, the order of rea
ction with respect to NO appears to be near unity in the gasification
regimes and two in the low-temperature chemisorption regime. The appar
ent order in gasification is strongly influenced by the presence of CO
in the reactant gas stream, and in certain reaction configurations th
e CO may be self-generated. In the presence of CO, the apparent order
with respect to NO decreases, and there are several reports of apparen
t fractional order. Other oxidizing gases (e.g. O-2, H2O) can also inf
luence the kinetics and course of the NO-carbon reaction. The thermal
history of the carbon can have a significant effect on its reactivity
in NO. It appears however that the annealing of carbons towards NO can
not be reliably predicted from the annealing behaviour of the carbons
towards other oxidizing gases (i.e. O-2) Reaction rates of NO with car
bon can also be influenced by the presence of mineral matter. There is
no general agreement on the quantitative importance of mineral cataly
sis in the reaction of carbons with NO. (C) 1997 Elsevier Science Ltd.