Adsorption, activation, and oxidation of ammonia over SCR catalysts
- Universita di Genova, Genoa (Italy); and others
The catalytic activity in the reduction of NO by ammonia in the presence of oxygen (SCR process) is reported for CuO-TiO{sub 2} and for different catalysts belonging to the MgO-Fe{sub 2}O{sub 3} system. These materials show high activity even at relatively low temperatures, with a maximum NO conversion near 520 K (CuO-TiO{sub 2}) and 600 K (MgO-Fe{sub 2}O{sub 3}). At higher temperatures, NO conversion is reduced because of the competitive NH{sub 3} oxidation by O{sub 2} to NO{sub x} and N{sub 2}. The adsorption and transformation of ammonia over these systems has been investigated by FT-IR spectroscopy in vacuum and in contact with oxygen and NO. In all cases ammonia is first coordinated over Lewis sites and later undergoes hydrogen abstraction giving rise either to NH{sub 2} amide species or to its dimeric form N{sub 2}H{sub 4}, hydrazine, detected over CuO-TiO{sub 2} and {gamma}-Fe{sub 2}O{sub 3}. Other species tentatively identified as imide NH, nitroxyl HNO, nitrogen anions N{sub 2}{sup -}, and azide anions N{sub 3}{sup -} are produced further. In the presence of NO, coordinated ammonia rapidly disappears, the above intermediates are not found, and water is produced, showing that the SCR reaction occurred. Ammonia protonation to ammonium ion is not detected at all over these systems. It seems consequently demonstrated that Bronsted acidity is not necessary for the appearance of SCR activity. A comparison with the previously-published data on V{sub 2}O{sub 5}-TiO{sub 2}-based systems is done and mechanisms of ammonia oxidation by oxygen and by NO are proposed. 64 refs., 8 figs., 3 tabs.
- OSTI ID:
- 224021
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 2 Vol. 157; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
Similar Records
Characterization and reactivity of V{sub 2}O{sub 5}--MoO{sub 3}/TiO{sub 2} de-NO{sub x} SCR catalysts
FTIR and kinetic studies of the mechanism of Fe{sup 3+}-exchanged TiO{sub 2}-pillared clay catalyst for selective catalytic reduction of NO with ammonia
Kinetics of the selective reduction of NO with NH{sub 3} over a V{sub 2}O{sub 5}(WO{sub 3})/TiO{sub 2} commercial SCR catalyst
Journal Article
·
Mon Oct 25 00:00:00 EDT 1999
· Journal of Catalysis
·
OSTI ID:20003842
FTIR and kinetic studies of the mechanism of Fe{sup 3+}-exchanged TiO{sub 2}-pillared clay catalyst for selective catalytic reduction of NO with ammonia
Journal Article
·
Mon Feb 14 23:00:00 EST 2000
· Journal of Catalysis
·
OSTI ID:20017451
Kinetics of the selective reduction of NO with NH{sub 3} over a V{sub 2}O{sub 5}(WO{sub 3})/TiO{sub 2} commercial SCR catalyst
Journal Article
·
Thu Jul 01 00:00:00 EDT 1999
· Journal of Catalysis
·
OSTI ID:684568