Rama Krishna Dadi

Krishna Gunugunuri, Hongmei An, Anand Srinivasan, Rohil

Daya, Yuhui Zha, Saurabh Joshi, Michael Cunningham, Krishna

Kamasamudram

Deactivation modes of DOCs

2

Introduction

▪ Precious metals like Pt and Pd are typically used in DOCs due to their superioroxidation capability

▪ Thermal aging and chemical aging of DOCs can result in their loss of oxidationperformance due to change in particle size and morphology of PGM particles

▪ Chemical aging of DOC is caused by inorganic elements present in diesel fuel andengine oil

▪ The deactivation due to S is recoverable with a thermal regeneration of DOC. Pdeactivation is irreversible under typical thermal regeneration events done indiesel after treatment system

▪ The objective of this work is to give general perspective on physical processesleading to different deactivation modes of DOCs

3

Outline of aging models

▪ Sintering type of models for PGM can be used to capture impact of HTA onoxidation performance

▪ Heat transfer model involving reaction heat source can capture solid temperatureexotherm inside DOC

▪ SOx poisoning models including SOx storage, SO2 oxidation and the impact onoxidation performance model can be used to capture impact of S on DOCperformance

▪ PGM oxidation rate is dependent on particle size, presence of S, and Pt: Pd ratio▪ P poisoning can be captured by two different sub-models. One for P accumulation

with engine operation, other for impact of P loading on oxidation performance

4

Hydrothermal Aging

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HTA impact on Oxidation Performance

1. Applied Catalysis B: Environmental 283 (2021) 119655

𝑑Ψ

𝑑𝑡= −𝑘𝑑 Ψ−Ψ∞

𝑛; Ψ∞ = 𝐴∞ exp −𝐸∞

𝑅𝑔𝑇𝑎𝑔𝑒

▪ Limiting process for Aging changes withextreme HTA

▪ Aging model with two sets of parameterswere developed: one for mild aging and theother extreme aging [1]

NO=200ppm

O2 =10%

6

HTA impact on PGM oxidation

▪ PGM Oxidation → Time on stream deactivation▪ Higher Pd → Lower PGM oxidation rate▪ Larger PGM particles→ Lower PGM oxidation rate [1]

1. Applied Catalysis B: Environmental 283 (2021) 119655

NO=1000ppm+O2=10%

NO=1000ppm+O2=10%

Higher Pd contentHigher Pt content

550°C-4h 550°C-4h700°C-50h

NO=1000ppm; O2 =10%

7

DOC solid temperature exotherm

0 200 400 600 800 1000 1200

time(s)

0

100

200

300

400

500

Inle

t Te

mp

era

ture

(°C

)

0

100

200

300

400

500

Exh

au

st fl

ow

(g/s

)

▪ In cylinder HC dosing to generate exotherm▪ Multiple thermocouples instrumented▪ Key heat transfer phenomena to be modeled

• Exotherm generation by HC oxidation• Radial heat loss• Axial heat convection

8

DOC Bed temperature exothermicity

▪ Model predicted solid temperature histogram is more appropriate to understandthe extent of thermal aging of PGM based catalysts

▪ Thermal gradients become particularly important for zone coated formulations

Data Model

9

Chemical Aging (S, P)

10

TPO on sulfated DOC

▪ TPO on catalyst saturated with S▪ Bimodal profile: Surface sulfates and bulk sulfates▪ Pt role: Migration of sulfur to support, oxidation of low oxidation states of S [2]

2. Applied Catalysis B: Environmental 181 (2016) 587–598

Data Model

11

Impact of SOx on oxidation performance

.

3. Catalysis Science & Technology, 5(3), pp.1731-1740

▪ Oxidation performance gets inhibited by S▪ Performance recovery dependent on DeSOx temperature and time▪ Facile PGM particles → More prone to S poisoning [3]▪ Model: S impact on oxidation

I. Surface S coverage (Slide. 10)II. Performance as a function of coverage

NO=1000ppm; O2 =10%

12

Impact of S on PGM oxidation

4600 4800 5000 5200 5400 5600 5800

time(s)

15

20

25

30

35

40N

O C

on

vers

ion

(%)

550°C-4h:Without S

Sulfated Catalyst

0 2000 4000 6000 8000 10000 12000 14000

time(s)

0

20

40

60

80

100

NO

Co

nv

ers

ion

(%)

0

50

100

150

200

250

300

350

400

450

500

Cat

in T

em

pera

ture

(°C

)

Model

Data

Temperature = 250°C

4. Catalysis Today 258 (2015) 169–174

▪ S on catalyst protects PGM from getting oxidized [4]▪ Sulfated catalyst with reductants in the feed → Significantly suppressed PGM oxidation

13

Real World Aged DOCs – NO oxidation

▪ Impact of P on Oxidation – Reactor and Elemental characterization of RWA DOCs▪ Oxidation performance before and after acid washing▪ Acid washing → Removes irreversible chemical contaminants▪ ICP analysis before and after acid washing▪ Activity recovered showed good trend with irreversible P but not S

NO=1000ppm; O2 =10%

5. SAE 2005-01-1758

14

HC Oxidation

▪ Same experimental tests as NO oxidation▪ Aging model framework is same as NO oxidation

▪ Aging parameters can be different

P removed (g/l)

15

Conclusions

▪ Real world aged DOCs can be represented by hydro-thermal aging, regardless ofactual dominant mode of deactivation

▪ Irreversible S present on catalyst suppresses deactivation due to PGM oxidesformation

▪ Deactivation of catalysts showed clear trend with P loading on catalyst surface

▪ Mimicking real world P loading of catalyst is important to simulate field deactivationdue to P

16

Acknowledgements (Advanced Chemical

System Integration team at Cummins)

17

Q+A

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