Selective reduction of NO by NH{sub 3} over chromia on titania catalyst: Investigation and modeling of the kinetic behavior
- Swiss Federal Institute of Technology, Zurich (Switzerland); and others
The kinetics and the parametric sensitivity of the selective catalytic reduction (SCR) of NO by NH{sub 3} were investigated over a chromia on titania catalyst. The chromium oxide phase was made up predominantly of X-ray amorphous Cr{sub 2}O{sub 3}. High SCR activity and selectivity to N{sub 2} was attained at low temperatures. The high selectivity is attributed to the absence of significant amounts of CrO{sub 2} and crystalline {alpha}-Cr{sub 2}O{sub 3} which favor N{sub 2}O formation. The selectivity to N{sub 2}O increased with higher temperature. Addition of up to 6% H{sub 2}O to the dry feed reduced the rate of NO conversion and decreased the undesired formation of N{sub 2}O. The effect of water on the catalytic behaviour was reversible. In the absence of oxygen, the reaction between NO and NH{sub 3} became marginal, independently whether H{sub 2}O was present or not. Small amounts of oxygen were sufficient to restore SCR activity. Admission of SO{sub 2} to the SCR feed resulted in a severe loss of activity. The poisoning of the catalyst by SO{sub 2} was already notable for low SO{sub 2} concentrations (30 ppm) and for temperatures up to 573 K. X-ray photoelectron and FTIR spectroscopy revealed the presence of sulfate species on the catalyst surface. Analysis of the kinetic data indicated that the SCR reaction in first order in NO and zeroth order in NH{sub 3} for temperatures in the range 400-520 K. The estimated activation energies for dry and wet feed amounted to 60.0 {+-} 1.6 kJ/mol (95 confidence limits). For temperatures in the range 400-520 K, and for a SO{sub 2} free feed, the steady-state kinetic data could be well described with a model based on an Eley-Rideal type reaction between activated ammonia surface species and gaseous or weakly adsorbed NO. 40 refs., 11 figs., 1 tab.
- OSTI ID:
- 478775
- Journal Information:
- Journal of Catalysis, Vol. 166, Issue 2; Other Information: PBD: Mar 1997
- Country of Publication:
- United States
- Language:
- English
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