CO Effects on Pd-BEA and Pd-ZSM-5 as Model Catalysts for ... · The authors gratefully acknowledge...
Transcript of CO Effects on Pd-BEA and Pd-ZSM-5 as Model Catalysts for ... · The authors gratefully acknowledge...
DPF
SCR
ASC
Urea injection
DRIFTs and bench-scaled reactor Experiments
CO Effects on Pd-BEA and Pd-ZSM-5 as Model Catalysts for Passive NOx Adsorption
Yuntao Gu1, Sreshtha Sinha Majumdar2, Josh A. Pihl2, Todd J. Toops2 and William S. Epling1
1 University of Virginia, 2 Oak Ridge National Laboratory
In-situ DRIFTs Study & Proposed PNA Mechanism
𝑍− 𝑃𝑑 𝐼𝐼 𝑁𝑂 𝑍−
𝑍− 𝑃𝑑 𝐼 𝑁𝑂1838 cm-1
𝑍− 𝑃𝑑 𝐼𝐼 𝑂𝐻
𝑍− 𝑃𝑑 𝐼𝐼 𝐻2𝑂 𝑛 𝑂𝐻
𝑍− 𝑃𝑑 𝐼𝐼 𝑁𝑂 𝑂𝐻 +2NO1818 cm-1
@T<100°C
NO2
+CO,NO𝑍− 𝑃𝑑 𝐼𝐼 𝑁𝑂 𝐶𝑂 𝑂𝐻1818 cm-1
CO2, CO and NO
2130
1873
1838
16401583
1873
1838
1873
1838
1818
18181873
1838
18181818
1873
1838
1873 cm-1
• 2130: [𝑁𝑂 − 𝐻]𝑍−
• 1640: 𝑁𝑂2+ − 𝑍−
• 1583: 𝑁𝑂+−𝑍−
• 1873: 𝑍− 𝑃𝑑 𝐼𝐼 𝑁𝑂 𝑍−
• 1838: 𝑍− 𝑃𝑑 𝐼 𝑁𝑂
• 1818: 𝑍− 𝑃𝑑 𝐼𝐼 𝑁𝑂 𝑂𝐻 & 𝑍− 𝑃𝑑 𝐼𝐼 𝑁𝑂 𝐶𝑂
𝑍−[𝑃𝑑(𝐼𝐼)] 𝑍− + 2𝐻2𝑂 → 𝑍− 𝑃𝑑 𝐼𝐼 𝑂𝐻 + [𝐻2𝑂 − 𝐻]𝑍−
2𝑍− 𝑃𝑑 𝐼𝐼 𝑁𝑂 𝑂𝐻 → 2𝑍− 𝑃𝑑(𝐼) + 𝑁𝑂 + 𝑁𝑂2 +𝐻2𝑂
2𝑍− 𝑃𝑑 𝐼𝐼 𝑁𝑂 𝐶𝑂 𝑂𝐻 → 2𝑍− 𝑃𝑑 𝐼 + 2𝑁𝑂 + 𝐶𝑂2 +𝐻2𝑂 + 𝐶𝑂
DRIFTs Peak Assignment
Dominating Surface Reaction
Temperature Programmed Desorption
• Simultaneous release of NO and CO starting from 175°C confirms the existence of:
𝑍− 𝑃𝑑 𝐼𝐼 𝑁𝑂 𝐶𝑂 𝑂𝐻 , the step change of the CO oxidation activity at 175°C indicates a different Pdn+
site distribution caused by the proposed surface reaction:
• O2 concentration affects Pdn+ site distribution leading to different CO light-off behaviors and NOx desorption
profiles, while NOx storage capacity is not affected.
2𝑍− 𝑃𝑑 𝐼𝐼 𝑁𝑂 𝐶𝑂 𝑂𝐻 → 2𝑍− 𝑃𝑑 𝐼 + 2𝑁𝑂 + 𝐶𝑂2 +𝐻2𝑂 + 𝐶𝑂
Motivation: Cold Start Emission Control
PNA+DOC
NOx
CO
PM
HC
CO2
H2ON2
PNA Adsorption Chemistry
Acknowledgement
The authors gratefully acknowledge support from the Department of Energy, Vehicle Technologies Office (DE-EE0008233)This research was supported in part by an appointment to the Oak Ridge National Laboratory ASTRO Program, sponsoredby the U.S. Department of Energy and administered by the Oak Ridge Institute for Science and Education
Comparison between Pd-ZSM-5 and Pd-BEA
Fresh CO Exposed
H2 Reduced Re-Oxidized
• NOx TPD profiles of both Pd-BEA and Pd-ZSM-5 consists of two desorption features.• Similar short-term CO effects on desorption characteristics are observed• Pd-BEA seems to suffer an irreversible loss of NOx storage capacity caused by CO
exposure, while the NOx storage capacity of Pd-ZSM-5 is relatively consistent.• Transient CO release happens only on Pd-ZSM-5
Similarity and difference
NO
(p
pm
)C
O (
pp
m)
1 4 7 10 ×13O2 (%):
175 °C
0 5 7 9 ×11CO2 (%): +13
NO
(p
pm
)C
O (
pp
m)
75 100 125 150 ×175T (°C): +200 −225
NO
(p
pm
)C
O (
pp
m)
Experimental Methodology
• Pd loading: 50 g/ft3 (1.8 g/l)• Washcoated on a 400 cells/in2 cordierite monolith• Loaded in automated synthetic exhaust flow reactor• Degreened at 600 °C for 4 h under 10% O2, 7% H2O and N2
Pd-exchanged ZSM-5
MultiGasTM 2030
Pri
smaP
lusT
M
TPD @ 20 °C/minCO on NO on NO offPicture from Thermo Scientific
Hydrothermal aging conditions
O210%
H2O 7%
T 600°C
SV 30000 h-1
Pretreat, cool conditions
O2 10%
H2O 0%
T 550°C
NO exposure conditions
NO 200 ppm
CO 200 ppm (0 or 200)
O2 10%
H2O 4.5% (0-4.5%)
CO2 0%
T 100°C
US DoE DEER Conference 2011 - Cary Henry, Hai-Ying Chen et. Al
CO NH2 2 + H2O → CO2+2NH3
𝐔𝐫𝐞𝐚 𝐇𝐲𝐝𝐫𝐨𝐥𝐲𝐬𝐢𝐬
𝐃𝐢𝐞𝐬𝐞𝐥 𝐎𝐱𝐢𝐝𝐚𝐭𝐢𝐨𝐧
CnHm +(n +𝑚
2)O2 → nCO2 +
𝑚
2H2O
CO +1
2O2 → CO2
O2 + 4NO + 4NH3 → 6H2O +4N2
Selective Catalytic Reduction
Ammonia Oxidation3
2O2 + 2NH3 → 3H2O +N2
NOx Release
NO∗ → NOx+ ∗NO + ∗→ NO∗𝐏𝐚𝐬𝐬𝐢𝐯𝐞 𝐍𝐎𝐱 𝐚𝐝𝐬𝐨𝐫𝐩𝐭𝐢𝐨𝐧