1

Tayebeh Hamzehlouyan, Chaitanya Sampara, Junhui Li, Ashok Kumar and Bill Epling

Background (S impact on LNT)

2 L. Olsson, M. Fredriksson, R.J. Blint, Appl. Catal. B 100(2011)31. J.-S. Choi, W.P. Partridge, J.A. Pihl, C.S. Daw, Catalysis Today 136(2008)173.

Known and significant impact on LNT catalysts

Background (S impact on SCR)

3 Y. Cheng, C. Montreuil, G. Cavataio and C. Lambert, SAE Technical Paper Series 2009-01-0898.

Known and significant impact on SCR catalysts

Background (S impact on oxidation catalysis)

4 J.-Y. Luo, D. Kisinger, A. Abedi, W.S. Epling, Appl. Catal. A 383(2010)182. H.C. Yao, H.K. Stepien and H.S. Gandhi, Journ. Catal.67(1981)231.

Known and significant impact on DOCs

SO2 oxidation SO2 oxidation over Pt-based catalysts

– SO2/SO3 adsorption have highest sensitivity coefficients

– Most studies based on large SO2 concentrations – Dawody, S poisoning of LNTs

5

Experimental Methodology

• Pt/Al2O3 catalyst – 50 g/ft3 Pt, 6% dispersion (CO chemisorption)

• MKS 2030 FTIR for gas-phase analysis – SO2 and SO3 calibrations built in-house – Instrument modified with ZnSe/MgF2 windows – Restek coated lines

• Steady-state conditions established for data to be shown

6

7

Effect of pretreatment

Pretreatment methods: N2 purge N2 at T≈600°C for 1 hour

SO2 pretreatment 50 ppm SO2 at T≈240°C overnight

Feed: [SO2] = 100 ppm [SO3] = 75 ppm [O2] = 10%

322 SOO21SO ↔+

0%

20%

40%

60%

80%

100%

200 300 400 500 600

SO2 C

onve

rsio

n

Temperature (°C)

N2 purge at 600C SO2 pretreatment

8

Effect of pretreatment

Pretreatment methods: N2 purge N2 at T≈600°C for 1 hour

SO2 pretreatment 50 ppm SO2 at T≈240°C overnight

Feed: [SO2] = 100 ppm [SO3] = 75 ppm [O2] = 10%

322 SOO21SO ↔+

0.0E+00

1.0E-07

2.0E-07

3.0E-07

4.0E-07

200 300 400 500 600

Rate

(mol

SO

2/s)

Temperature (°C)

N2 purge at 600C SO2 pretreatment

9

Data reproducibility

T (°C) SO2(ppm) SO3(ppm) O2(%)

231.4 100 50 10

241.5 150 100 10

241.5 50 0 10

285.4 100 0 5

285.4 50 100 7

262.2 100 0 5

318.2 100 0 10

286.0 100 0 10

0%

20%

40%

60%

80%

200 250 300 350

SO2 C

onve

rsio

n

Temperature (°C)

“Long” pretreatment critical in obtaining good reproducibility

10

Effect of SO2 on performance

0%

10%

20%

30%

40%

50%

20 50 80 110 140 170

Conv

ersi

on

SO2 concentration (ppm)

T=240C T=263C T=286C T=308C

α = 0.74

α = 0.95

α = 1.00

α = 0.87

-20

-19

-18

-17

-16

-15

-14 2 3 4 5 6

ln(r

ate)

ln (SO2 concentration)

Change in SO2 concentration leads to similar conversions first order dependence

11

Effect of O2 and SO3

0%

5%

10%

15%

20%

25%

5 10 15

Conv

ersi

on

O2 concentration (%)

T=240C T=285C

O2 seems to have a slight negative effect on SO2 oxidation

0%

10%

20%

30%

40%

0 40 80 120 Co

nver

sion

SO3 concentration (ppm)

T=263C T=285C

SO3 has a definite negative impact (product inhibition)

12

SO2 oxidation over Pt/Al2O3:

Reaction rate dependencies summary

322 SOO21SO ↔+ -rSO2 = k[SO2]α[O2]β[SO3]γ

13

Activation energy

Ea/R=7107 R² = 0.999

Ea/R=7272 R² = 0.991

Ea/R= = 11066 R² = 0.998

Ea/R=12451 R² = 0.992

Ea/R=12080 R² = 1.000

Ea/R=13750 R² = 0.995

Ea/R=12192 R² = 0.996

Ea/R=11889 R² = 0.997

Ea/R=11621 R² = 0.989

-19.5

-19.0

-18.5

-18.0

-17.5

-17.0

-16.5

-16.0

-15.5

-15.0

-14.5 0.0016 0.0017 0.0018 0.0019 0.0020

ln(-r

A)

1/T (K-1)

SO2=100 ppm, SO3=0 ppm, O2=5%

SO2=100 ppm, SO3=0 ppm, O2=10%

SO2=50 ppm, SO3=100 ppm, O2=7%

SO2=150 ppm, SO3=50 ppm, O2=6%

SO2=50 ppm, SO3=100 ppm, O2=10%

SO2=100 ppm, SO3=50 ppm, O2=10%

SO2=100 ppm, SO3=100 ppm, O2=10%

SO2=150 ppm, SO3=100 ppm, O2=10%

SO2=100 ppm, SO3=75 ppm, O2=10%

14

Activation energy

Ea/R=7107 R² = 0.999

Ea/R=7272 R² = 0.991

Ea/R= = 11066 R² = 0.998

Ea/R=12451 R² = 0.992

Ea/R=12080 R² = 1.000

Ea/R=13750 R² = 0.995

Ea/R=12192 R² = 0.996

Ea/R=11889 R² = 0.997

Ea/R=11621 R² = 0.989

-19.5

-19.0

-18.5

-18.0

-17.5

-17.0

-16.5

-16.0

-15.5

-15.0

-14.5 0.0016 0.0017 0.0018 0.0019 0.0020

ln(-r

A)

1/T (K-1)

SO2=100 ppm, SO3=0 ppm, O2=5%

SO2=100 ppm, SO3=0 ppm, O2=10%

SO2=50 ppm, SO3=100 ppm, O2=7%

SO2=150 ppm, SO3=50 ppm, O2=6%

SO2=50 ppm, SO3=100 ppm, O2=10%

SO2=100 ppm, SO3=50 ppm, O2=10%

SO2=100 ppm, SO3=100 ppm, O2=10%

SO2=150 ppm, SO3=100 ppm, O2=10%

SO2=100 ppm, SO3=75 ppm, O2=10%

15

Effect of presence/absence of SO3 on Ea

16

Effect of water

0%

20%

40%

60%

80%

100%

200 250 300 350 400 450

SO2 C

onve

rsio

n

Temperature (°C)

Feed: [SO2]=98ppm [O2]=5%, [H2O]=5%

T (°C)

SO2 Conversion

no water 5% water

262 21.9% 19.6%

307 60.7% 41.4%

351 94.7% 73.9%

17

Effect of water

0%

20%

40%

60%

80%

100%

200 250 300 350 400 450

SO2 C

onve

rsio

n

Temperature (°C)

Feed: [SO2]=98ppm [O2]=5%, [H2O]=5%

T (°C)

SO2 Conversion

no water 5% water

262 21.9% 19.6%

307 60.7% 41.4%

351 94.7% 73.9%

At 351C: SO2 out = 25 ppm SO3 out = 1.4 ppm H2SO4 out = 70 ppm

Model Set-up • Differential data (high temperature guided by thermo) • Assumed isothermal (ΔHSO2 SO3 mildly exothermic) • Assumed steady state

• Objective function:

• First, each reaction optimized individually without

altering other rates

=

elXX

sumdataptsnum

normmod

exp2log*_

1

--- (1,2)

--- (3,4)

--- (5,6)

--- (7,8)

Comparison of individual reaction optimization Reaction optimized

Objective function

Literature 1.743 SO2 ads – des 0.278 O2 ads – des 0.309 SO2*+O* (fwd-rev) 0.528 SO3 ads – des 1.70

200 250 300 350 400 450 500 550 600-80

-60

-40

-20

0

20

40

60

80

100

Temperature [C]

Con

vers

ion

- SO

2

Literature

SO2ads-des

O2ads-des

SO2+O

SO3ads-des

Experiment

Model suggests the rate is highly sensitive to SO2 and O2 adsorption-desorption kinetics, and some to surface rxn

Further optimization Since the model suggests the rate is highly sensitive to SO2 and O2 adsorption-desorption kinetics, parameters from these reaction steps were used for further optim.

100 101 102 103100

101

102

103

∆ xexpt

∆ x

mod

el

Optimized for reaction rates that showed highest norm variation - r2, r3, r4, r5, r6 Optimized for rate parameters which showed maximum change - A3, A4, A5, A6, E3

Reaction optimized

Objective function

Literature 1.743 A3,A4,A5,A6,E3 0.0375

Modeling validation

21

SO2 = 100 ppm, SO3 = 75 ppm, O2 = 10% SV = 25000 h-1

SO2 = 200 ppm, SO3 = 0 ppm, O2 = 10% SV = 25000 h-1

0

20

40

60

80

100

150 250 350 450 550

Conv

ersi

on

Temperature (C)

Expt Data

Model (opt)

Model (lit values)

0

20

40

60

80

100

150 250 350 450 550 Co

nver

sion

Temperature (C)

Expt Data

Model (Opt)

Model (lit values)

Modeling RDS

22

1 2 3 4 5 6 7 80

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

200oC

RDS @200oC

1 2 3 4 5 6 7 80

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

300oC

RDS @300oC

1 2 3 4 5 6 7 80

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

400oC

RDS @400oC

1 2 3 4 5 6 7 8

0

2

4

6

8

10

12

14

16

18

500oC

RDS @500oC

Surface coverages

23

0.984

0.988

0.992

0.996

1

0 0.5 1

Cove

rage

Normalized Length

240C 300C 400C 500C

0.E+00

1.E-05

2.E-05

3.E-05

4.E-05

5.E-05

0 0.5 1

Cove

rage

Normalized Length

240C 300C 400C 500C

SO2

O2

0.0E+00

4.0E-03

8.0E-03

1.2E-02

1.6E-02

0 0.5 1

Cove

rage

Normalized Length

240C 300C 400C 500C

SO3

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

0 0.5 1

Cove

rage

Normalized Length

240C 300C 400C 500C

Vacancies

Conclusions • DOC readily converts SO2 SO3

– T > 225°C • SO3 and O2 inhibit the reaction • Modeling suggests that the reaction is quite

sensitive to O2 and SO2 adsorption/desorption kinetics, but that the surface reaction (SO2 + O SO3) is rate determining.

24

Conclusions • DOC readily converts SO2 SO3

– T > 225°C • SO3 and O2 inhibit the reaction • Modeling suggests that the reaction is quite

sensitive to O2 and SO2 adsorption/desorption kinetics, but that the surface reaction (SO2 + O SO3) is rate determining.

• In other words we don’t know much yet • Somewhat Déjà-Vu with NO oxidation kinetics

25

Acknowledgements • Thanks to Cummins for financial support • Thanks to JM for catalyst samples

26