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

Journal Article · Wed Jan 31 00:00:00 EST 2018 · Catalysis Today

DOI:https://doi.org/10.1016/j.cattod.2018.01.027· OSTI ID:1471840

Sinha Majumdar, Sreshtha  ^[1]; Alexander, Anne-Marie ^[2]; Gawade, Preshit ^[2]; Celik, Gokhan ^[2]; Ozkan, Umit S. ^[2]

---

1. The Ohio State Univ., Columbus, OH (United States). William G. Lowrie Dept. of Chemical and Biomolecular Engineering; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. The Ohio State Univ., Columbus, OH (United States). William G. Lowrie Dept. of Chemical and Biomolecular Engineering

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_x/CeO₂) 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 SO₂ in the feed. The ratio of the reduction to oxidation catalyst was also seen to affect the hydrothermal stability under wet conditions with SO₂ 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_x conversion and improved CH₄ conversions when the dual-catalyst bed was kept on-stream for 40 h^-1. X-ray photoelectron spectroscopy on samples poisoned with SO₂ ex-situ revealed the deposition of surface sulfates on the Pd/SZ catalyst samples and a combination of sulfates and sulfites on the CoO_x/CeO₂ on treatment with SO₂. The presence of alumina in the Pd/SZ sample protects the support from SO₂ poisoning as the oxidation state of the zirconia support remained largely unchanged on poisoning while in the CoO_x/CeO₂ sample, sulfur poisoning likely affects the cerium redox cycle (Ce³⁺-Ce⁴⁺). ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR) revealed redistribution of the octahedral and tetrahedral Al-O coordination on SO₂ 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.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); The Ohio State Univ., Columbus, OH (United States)
• Sponsoring Organization: USDOE; Caterpillar Inc., Peoria, IL (United States)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1471840
• Journal Information: Catalysis Today, Vol. 320; ISSN 0920-5861
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
33 ADVANCED PROPULSION SYSTEMS
NOx reduction
Lean-burn
SO2 tolerance
XPS
27Al MAS NMR