Abstract
Catalysts used for selective catalytic reduction were deactivated for various times in a slipstream from a municipal solid waste incineration plant and then characterized. The activity for NO reduction with NH3 was measured. The Brunauer–Emmett–Teller surface areas were determined by N2 adsorption from which the pore size distributions in the mesopore region were obtained. Micropore areas and volumes were also obtained. The composition of fresh and deactivated catalysts as well as fly ash was determined by atomic absorption spectroscopy and scanning electron microscopy with energy dispersive X-ray analysis. The changes in surface area (8% decrease in BET surface area over 2311 h) and pore structure were small, while the change in activity was considerable. The apparent pre-exponential factor was 1.63 × 105 (1/min) in the most deactivated catalyst, compared to 2.65 × 106 (1/min) in the fresh catalyst, i.e. a reduction of 94%. The apparent activation energy for the fresh catalyst was 40 kJ/mol, decreasing to 27 kJ/mol with increasing deactivation. Characterization showed that catalytic poisoning is mainly due to decreased acidity of the catalyst caused due to increasing amounts of Na and K.Graphical
Highlights
In a recent study, selective catalytic reduction (SCR) was compared to selective non-catalytic reduction (SNCR) for the reduction of nitrogen oxides (NOx) [1]
We have reported on the deactivation of SCR catalysts after use for 2000 h in the treatment of flue gases from a MSWI plant [7]
Four of them were placed in a deactivation chamber in a slipstream from the main flue gas channel, with gas flowing from top to bottom
Summary
Selective catalytic reduction (SCR) was compared to selective non-catalytic reduction (SNCR) for the reduction of nitrogen oxides (NOx) [1]. Fly ash contains many potentially poisonous compounds, of which alkali metals are of the greatest concern [2–4]. These will cause deactivation of the catalysts, by blocking the Brønsted acid sites, as in the case of the burning forest residues [3, 5]. We have reported on the deactivation of SCR catalysts after use for 2000 h in the treatment of flue gases from a MSWI plant [7]. In this latter study, alkali metals and some other metals were shown to deactivate the catalyst to a high degree. The components of fly ash determine the degree of the deactivation of the catalyst
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