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