Steam effect on NO
x
reduction over lean NO
x
trap Pt–BaO/Al2O3 model catalyst |
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Authors: | Xiaoyin Chen Johannes Schwank |
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Affiliation: | (1) Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109-2136, USA |
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Abstract: | The effect of steam on NO
x
reduction over lean NO
x
trap (LNT) Pt–Ba/Al2O3 and Pt/Al2O3 model catalysts was investigated with reaction protocols of rich steady-state followed by lean–rich cyclic operations using
CO and C3H8 as reductants, respectively. Compared to dry atmosphere, steam promoted NO
x
reduction; however, under rich conditions the primary reduction product was NH3. The results of NO
x
reduction and NH3 selectivity versus temperature, combined with temperature programmed reduction of stored NO
x
over Pt–BaO/Al2O3 suggest that steam causes NH3 formation over Pt sites via reduction of NO
x
by hydrogen that is generated via water gas shift for CO/steam, or via steam reforming for C3H8/steam. During the rich mode of lean–rich cyclic operation with lean–rich duration ratio of 60 /20 s, not only the feed NO,
but also the stored NO
x
contributed to NH3 formation. The NH3 formed under these conditions could be effectively trapped by a downstream bed of Co2+ exchanged Beta zeolite. When the cyclic operation was switched into lean mode at T < 450 °C, the trapped ammonia in turn participated in additional NO
x
reduction, leading to improved NO
x
storage efficiency. |
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Keywords: | lean NO x trap NO x reduction Pt– BaO/Al2O3 catalyst NH3 steam cobalt-exchanged beta zeolite |
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