Effect of alumina incorporation on the sulfur tolerance of the dual-catalyst aftertreatment system for reduction of nitrogen oxides under lean conditions [electronic resource]

• Ngôn ngữ: eng
• Ký hiệu phân loại: 629.8 Automatic control engineering
• Thông tin xuất bản: Oak Ridge, Tenn. : Oak Ridge, Tenn. : Oak Ridge National Laboratory ; Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2018
• Mô tả vật lý: Size: p. 204-213 : , digital, PDF file.
• Bộ sưu tập: Metadata
• ID: 266501
• Chủ đề: 1. 03 natural gas; 2. 33 advanced propulsion systems; 3. 37 inorganic, organic, physical, and analytical chemistry; 4. Lean-burn; 5. Nox reduction

Tóm tắt

 Presence of sulfur or sulfur additives in natural gas lead to the formation of sulfur dioxide in the exhaust stream of natural gas-fired lean-burn engines. The sulfur tolerance and hydrothermal stability of the dual-catalyst aftertreatment system comprising a reduction catalyst (palladium supported on sulfated zirconia- Pd/SZ) and an oxidation catalyst (cobalt oxide supported on ceria- CoO<
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 x<
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 /CeO<
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 2<
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 ) for NOx reduction under lean-burn conditions has been tested under simulated engine exhaust conditions. Alumina-incorporated Pd/SZ (Pd/SZ(Alumina)) reduction catalyst as part of the dual catalyst bed demonstrated superior sulfur tolerance in the presence of 5 ppm SO<
 sub>
 2<
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  in the feed. The ratio of the reduction to oxidation catalyst was also seen to affect the hydrothermal stability under wet conditions with SO<
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 2<
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  in the reaction medium. The effect of hydrocarbon and water concentration in the reaction mixture on the sulfur tolerance of the dual-catalyst bed was studied. Increasing the reaction temperature from 450�C to 500�C demonstrated very stable NO<
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  conversion and improved CH<
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 4<
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  conversions when the dual-catalyst bed was kept on-stream for 40 h<
 sup>
 -1<
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 . X-ray photoelectron spectroscopy on samples poisoned with SO<
 sub>
 2<
 /sub>
  ex-situ revealed the deposition of surface sulfates on the Pd/SZ catalyst samples and a combination of sulfates and sulfites on the CoO<
 sub>
 x<
 /sub>
 /CeO<
 sub>
 2<
 /sub>
  on treatment with SO<
 sub>
 2<
 /sub>
 . The presence of alumina in the Pd/SZ sample protects the support from SO<
 sub>
 2<
 /sub>
  poisoning as the oxidation state of the zirconia support remained largely unchanged on poisoning while in the CoO<
 sub>
 x<
 /sub>
 /CeO<
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 2<
 /sub>
  sample, sulfur poisoning likely affects the cerium redox cycle (Ce<
 sup>
 3+<
 /sup>
 -Ce<
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 4+<
 /sup>
 ). <
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 27<
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 Al magic angle spinning nuclear magnetic resonance (MAS NMR) revealed redistribution of the octahedral and tetrahedral Al-O coordination on SO<
 sub>
 2<
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  poisoning. Due to association with deposited sulfates on the catalyst, shielding effect on the Al nuclei resulted in an increased octahedral Al-O coordination in the poisoned sample.