Adsorption & Desorption of NO on a Passive NOx Adsorber Josh A. Pihl (pihlja@ornl.gov), Sreshtha Sinha Majumdar

Oak Ridge National Laboratory Fuels, Engines, and Emissions Research at the National Transportation Research Center

Acknowledgement: Funding provided by DOE Vehicle Technologies Office (Ken Howden, Gurpreet Singh, Leo Breton)

• Reducing petroleum consumption and GHG

emissions will require higher efficiency engines

• Increasing engine efficiency will result in lower

exhaust temperatures, especially for lean burn

engines

– longer cold start times

– very low exhaust temperatures at low loads

• NOx control catalysts (SCR, LNT, TWC) do not

work effectively at temperatures below 200 °C

• Passive NOx Adsorbers (PNA) components

provide an option for dealing with low

temperature NOx control1

– trap NO at low temperatures

– release trapped NO at higher temperatures

after downstream NOx conversion catalysts

are active

• PNAs were ranked a high priority by

respondents to the 2017 CLEERS Industry

Priorities Survey

– Highest priority among all technologies for

HD and LD diesel

– Second highest priority for MD diesel

• Design of PNA systems and control strategies

will rely on accurate simulation tools

• “Mechanisms and kinetics for NOx storage,

release, and conversion” was among the

highest ranked topics for HD, MD, and LD

diesel applications

• Modeling of NO adsorption energetics is

required to accurately capture storage capacity

and release temperatures

• This work aims to accurately measure and

model NO adsorption energetics on PNAs

Motivation

Approach

• Use an automated flow reactor to measure NO storage isotherms on a PNA core

sample provided by a catalyst supplier

• Degreen 4 h at 700 °C under 10% O2, 5% H2O

• Run NO adsorption/desorption experiments:

– pretreat 600 °C, cool to operating temperature

– increase NO in stepwise fashion, waiting for steady state at each step

– perform temperature programmed desorption to 600 °C

• Repeat at different temperatures, H2O concentrations, O2 concentrations

Conclusions

• Due to low NO uptake between concentration steps, stepwise adsorption

experiments are ineffective for measuring adsorption isotherms

• This PNA formulation shows sensitivity to oxidation state for both NO storage

capacity and stability; an accurate model would need to capture this effect

Future Work

• Develop new experimental approach that results in more NO uptake and more

precise adsorption isotherms

• Measure effects of reductant species (CO, hydrocarbons) on NO

adsorption/desorption

• Calculate NO adsorption enthalpies and identify PNA modeling strategies

References 1H.-Y. Chen, et al., SAE 2013-01-05355

Equilibrium storage modeling (preliminary)

NO Adsorption Isotherms and TPDs

NOin NOout

NO uptake

100 °C 300 °C

repeat

inte

grat

e

Adsorption Isotherms TPDs

0% H2O

0% O2

0% H2O

10% O2

5% H2O

0% O2

5% H2O

10% O2 100

107

115

125

136

150

167

188

214

250

300

T (°C)

HD

PF

PNA

HCT

SCR

DOC

TWC

LNT

other

LD MD Gasoline

6.5-10

5.5-6.5

4.5-5.5

3.5-4.5

0-3.5

Avg.

Score

Diesel

𝜃𝑖 =𝐾𝑖,𝑁𝑂𝑃𝑁𝑂

1 + 𝐾𝑖,𝑁𝑂𝑃𝑁𝑂

𝐾𝑖,𝑠 = 𝐾𝑖,𝑠,0𝑒−∆𝐻𝑖,𝑠 𝑅𝑇

𝐼𝑁𝑂 = 𝜔1𝜃1 (+𝜔2𝜃2)

One or two sites:

Langmuir isotherm:

Constant ads. enthalpy:

site 1

w (mol/l) 0.0039

Ki,NO,0 4.8E-3

DHi,NO (kJ/mol) -49

1 2

0.0016 0.0031

8.7E-5 3.7E-2

-68 -37

rep

eat

remap

• Inclusion of O2 increases total NO storage capacity, leads to lower temperature

release peaks in TPD

• Removal of H2O decreases total NO storage capacity, resulting in noisier

isotherms

– Future experiments will all be run with H2O

HD Diesel: mech. & kinetics

aging new PNA materials

poisoning GHG byproducts

MD Diesel: new PNA materials

mech. & kinetics aging

poisoning GHG byproducts

LD Diesel: new PNA materials

aging mech. & kinetics GHG byproducts

poisoning

Average Priority Score

Experiment schematic