DEER CONFERENCE 2011

Weiyong Tang, Xiwen Huang, and Sanath Kumar

BASF Corporation, Iselin, NJ

DEER Conference 2011, Detroit, MI

Tuesday, October 04, 2011

Sulfur Effect and Performance Recovery of 

a DOC + CSF + Cu-Zeolite SCR System 
DEER CONFERENCE 2011

Outline

 Introduction

 Zeolite-based SCR behavior

– Performance

– Sulfation issue: literature

 Reactor experiments to simulate transient behavior

 Accelerated low temperature sulfation behavior

 Sulfation effects and mechanism

 Desulfation methods

 Summary
DEER CONFERENCE 2011

Recent developments have led to Cu-zeolite SCR 

catalysts with remarkably improved low 

temperature activity and high thermal stability

SAE 2008-01-1025: Enhanced Durability of a Cu/Zeolite Based SCR Catalyst. Giovanni Cavataio, et al
DEER CONFERENCE 2011

On the other hand, Cu-zeolite SCR also provides 

benefit over V/Ti SCR for applications with “cold” 

exhaust that never see high temperatures

Temperature window of one HDD engine platform

and SCR NOx conversion

0

10

20

30

40

50

60

70

80

90

100

200 225 250 275 300 325 350 375 400

SCR in temperature (oC)

Time above temperature

and deNOx

Cu-SCR

V-SCR

Coldest cycle Average cycle
DEER CONFERENCE 2011

Zeolite SCR sulfation issue: literature

 Several recent presentations have highlighted effects of sulfur compounds 

on zeolite-based SCR performance

 “The Effects of SO2 and SO3 Poisoning on Cu/Zeolite SCR Catalysts”. 

Christine Lambert, et al: SAE 2009-01-0898

 “Investigation of Sulfur Deactivation on Cu/Zeolite SCR Catalysts in 

Diesel Application”. Yisun Cheng, et al: 2009 DEER Conference

 “The Effects of Sulfur Poisoning and Desulfation Temperature on the 

NOx Conversion of LNT+SCR Systems for Diesel Applications”. Joe 

Theis, et al: SAE 2010-01-0300

 Past experience from Euro IV applications has shown V/Ti SCR to be 

insensitive to sulfation, although overall NOx conversion may be lower than 

zeolite-based SCR
DEER CONFERENCE 2011

Background and motivation

 Background:

– Systems with active regeneration used in low sulfur environments 

have shown stable, sustained performance to end-of-useful life*

– Some systems running under high sulfur conditions and/or extended 

low temperature operation have shown performance loss

 Motivation:

– Better understanding of degradation mechanism

– Generate system-level performance features with realistic SCR-inlet 

SO2/SO3 and NO2/NOx in a DOC + CSF + Cu-SCR system

– Determination of conditions for system performance recovery

* The New Challenge -Heavy Duty Diesel Engine Emission Control. Sanath V Kumar; SIAT 2011 Keynote Presentation
DEER CONFERENCE 2011

Laboratory study of sulfation effect at 

system level

 Diesel System Simulator (DSS)

 System level study

 Capable of simulating various 

transient cycles 

– By matching temperature, space 

velocity and compositions from 

engine experiments

 Catalyst size

 DOC: 1.5"x3"

 CSF: 1.5"x6"

 SCR: 1.5"x6"

SO2

MS

FTIR

Cu-SCR CSF

1.5”x6”

1.5”x6”

NH3

DOC

1.5”x3”

FID

FID

DSS setup
DEER CONFERENCE 2011

Engine HDFTP data “derated” to simulate 

cold engine operation

Transient temperature and space

velocity profiles in the first four cycles

(200-300 C SCR inlet 

~55,000 h-1 peak SCR SV)

0 20 40 60 80

100

125

150

175

200

225

250

275

300

325

350

 DOC-in temp.

 SCR-in temp

Temperature (°C)

Run Time (min)

Temperatures in the first 4 FTP cycles of D3C3S6_061209_3 sulfation runs

0 20 40 60 80

0

10000

20000

30000

40000

50000

60000

70000

 SCR SV

Space Velocity (hr-1

)

Run Time (min)

High SO2 in feed to simulate extended sulfur 

exposure on engine:

• ~1.0 g/L sulfur exposure = 100 h on engine 

(using ULSD fuel)

• ~12.5 g/L sulfur exposure on reactor ≅ 1250 h

on engine (~35 PPM SO2 for 12 h in reactor)
DEER CONFERENCE 2011

System deactivation after accelerated 

sulfur exposure at low temperature 

Sulfur (SO2) breakthrough after 

different components

0 2 4 6 8 10 12 14

0

10

20

30

40

50

60

70

80

90

100

S

O2 overall consumption (%)

System sulfur exposure (g/L_SCR)

 Loss after DOC

 Loss after CSF

 Loss after SCR

System response to 12h continuous derated HDFTP cycles 

under 35 ppm SO2 in feed conditions

Approx. 1300 h on engine

Multiple derated FTP runs 

(200-300 C SCR in, NSR=1, 35ppm SO2 in feed) 

0 2 4 6 8 10 12 14

0

10

20

30

40

50

60

70

80

90

100

Conversion (%) or NO2/NOx (x100%)

System sulfur exposure (g/L_SCR)

CSF/O NO2/NOx

Cycle deNOx
DEER CONFERENCE 2011

After sulfur exposure, Cu-zeolite SCR 

became sensitive to NO2/NOx ratio, 

especially for T < 250 C

80 82 84 86 88 90 92 94 96 98 100

0

50

100

150

200

250

300

0.00

0.25

0.50

0.75

1.00

SCR Out NOx (ppm)

Run Time (min)

Temperature

NOx

SCR in NO2/NOx

 
DEER CONFERENCE 2011

Sulfur concentration gradients in Cu-SCR 

after 13 g/L_SCR sulfur exposure

Washcoat surface to substrate Front to rear

 Washcoat sulfur profile via EPMA Sulfate content via ICP wet analysis

1.5”x6”

0.0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3.0

Weight (%)

Distance (um)

Front core Middle core Rear core

0

5000

10000

15000

20000

25000

30000

35000

40000 Component Oxide Mass (ppm)

washcoat
DEER CONFERENCE 2011

TGA/DTA-MS of sulfated sample shows 

two major sulfation modes

‘Low-T’ sulfate

‘High-T’ sulfate

13 g/L sufated TEX-0088

13 g/L sufated TEX-0088

Absence of NH3 during sulfation

(NH4)2SO4 control

CuSO4 control

Sulfur release

and weight loss

(a)

(b)

(c)

(d)

Sulfated

Cu-SCR

CuSO4

(NH4)2SO4

Sulfated

Cu-SCR

(w/o NH3)
DEER CONFERENCE 2011

50

55

60

65

70

75

80

85

90

95

100 Cycle NOx conversion (%)

Set #1, NSR=1.5 @ deS (NSR=1.0 for 450°C deS)

Set #2, NSR=1.0 @ deS

Set #3, NSR=0.0 @ deS

NOx conversion recovery is incremental 

with temperature

NOx conversion (Baseline: ~95%, all evaluated at NSR=1.0)

 Parametric study for desulfation effectiveness

 NSR (NH3/NOx) = 0.0, 1.0, 1.5

 Durations = 0.5, 1.0 hr

 Temperature = 375, 400, 450, 500, 600 C (SCR in)

375C-1h

deSOx

400C-1h

deSOx

450C-0.5h

deSOx
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Full performance recovered at 500 C 

deSOx ... and does not further degrade 

during multiple sulfation-desulfation cycles

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30

System sulfur exposure (g/L_SCR)

deNOx and CSF out NO2/Nox (x100%)

deSOx@ 500 C NOx conversion

CSF out NO2/NOx

SO2 NH3

DOC CSF Cu-SCR

SO2 NH3

DOC CSF Cu-SCR NO2/NOx ratio and NOx conversion

after sulfation and desulfation

SO2

7 g/L_SCR

sulfation
DEER CONFERENCE 2011

DOC/CSF generated fairly repeatable 

HDFTP NO2/NOx profile in post-deSOx 

evaluations

0.00

0.25

0.50

0.75

1.00 2 

SCR in NO2/NOx

160 162 164 166 168 170 172 174 176 178 180

0.00

0.25

0.50

0.75

1.00 2 

SCR in NO2/NOx

After 1st

Sulfation-deSOx

After 3rd

Sulfation-deSOx
DEER CONFERENCE 2011

SCR-out NOx slip values were very similar 

after 500 C deSOx

 Baseline

After 7 g/L sulfation (SOx)

After 1st SOx-deSOx

After 2nd SOx-deSOx

After 3rd SOx-deSOx

After 4th SOx-deSOx

160 165 170 175 180

0

15

30

45

60

75

90

105

120

135

150

SCR out NOx Slip (ppm)

Run Time (min)

D5C5S15 SCR out NOx in the last cycle of different test stages
DEER CONFERENCE 2011

Summary

 Zeolite-based SCRs provide high thermal stability and durability in active 

regeneration systems with periodic high temperature exposures

 Literature reveals all zeolite-based SCRs are susceptible to sulfation under low 

temperature SO3 exposure

 This study has shown that Cu-Zeolite SCR degrades after severe sulfur 

exposure under extended low temperature conditions

 Two major sulfation modes are most likely involved

– Formation of (NH4)2SO4 or (NH4)HSO4

– Formation of CuSO4

 System performance can be recovered

 Temperature is the most important factor determining desulfation efficiency

 The system recovered most but not all of its performance after 450 C 

desulfation

 Upon 500 C desulfation, NOx conversion efficiency was fully restored and 

sustained in multiple sulfation-desulfation experiments 
DEER CONFERENCE 2011

Thank You!