T. Curtin et al., The catalytic oxidation of ammonia: influence of water and sulfur on selectivity to nitrogen over promoted copper oxide/alumina catalysts, CATAL TODAY, 55(1-2), 2000, pp. 189-195
The CuO/Al2O3 system is active for ammonia oxidation to nitrogen and water.
The principal by-products are nitrous oxide and nitric oxide. Nitrous oxid
e levels increase with the addition of various metal oxides to the basic co
pper oxide/alumina system. Addition of sulfur dioxide to the reaction strea
m sharply reduces the level of ammonia conversion, but has a beneficial eff
ect on selectivity to nitrogen. Added water vapour has a lesser effect on a
ctivity but is equally beneficial in terms of selectivity to nitrogen. The
CuO/Al2O3 is also active for the selective catalytic reduction of nitric ox
ide by ammonia, but this reaction is not effected by sulfur dioxide additio
n. A mechanism for ammonia oxidation to nitrogen is proposed wherein part o
f the ammonia fed to the catalyst is converted into nitric oxide. A pool of
monoatomic surface nitrogen species of varying oxidation states is establi
shed. N-2 or N2O are formed depending upon the average oxidation state of t
his pool. An abundance of labile lattice oxygen species on the catalyst sur
face leads to overoxidation and to N2O formation. On the other hand, reduce
d lability of surface lattice oxygen species favours a lower average oxidat
ion state for the monoatomic surface nitrogen pool and leads to N-2 formati
on. (C)2000 Elsevier Science B.V. All rights reserved.