Understanding the Deactivation Mechanisms of Cu/Zeolite

SCR Catalysts in

Diesel Application

Yisun Cheng, Christine LambertResearch & Innovation Center, Ford Motor Company

Ja

Hun Kwak, Charles H.F. PedenInstitute for Interfacial Catalysis, PNNL

August 5, 20082008 DEER Conference

2

Introduction

The effects of engine and lab aging on Cu/zeolite SCR catalysts reactivity and material properties

were assessed by performance tests and multiple characterization techniques that included 27Al NMR, XRD, and TEM.

The impacts of zeolite

structure, Cu sites, and active sites

on SCR catalyst durability are discussed.

The results aid the development of the understanding of Cu/zeolite

SCR catalyst

deactivation mechanisms in diesel application.

3

The Durability of Cu/Zeolite

SCR Catalysts

Zeolite Structure:Increasing the collapsing temp to maintain zeolite structure during thermal aging is the key for Cu/zeolite

SCR Catalysts in Diesel Application.

Active Sites

Durability

Cu Sites

4

Zeolite

Stability

Thermal Deactivation

Fresh (Cat A) Lab 860/30min (Cat A) Lab 770C/30min (Cat A)

770C/30min: Zeolite crystal structure maintained

860/30min: Zeolite structure collapsed. Large particles of amorphous alumino-silicate are formed (XRD)

No evidence for Cu sintering 0102030405060708090

100

100 150 200 250 300 350 400 450 500 550 600Catalyst Temperature, C

Con

vers

ion,

%NOx conv 100% NO FreshNOx conv 100% NO 770C 30minNOx conv 100% NO 860C 30min

5

Cordierite (honey comb)

Cat A

fresh

Cat A

770 C 30 min aged

Cat A

860 C 30 min aged

XRD (Cat A)

Zeolite structure mostly stable after 770 C treatments

Only amorphous phase remained after 860 C 30 min aged Zeolite structure collapsed for 860 C treatment

SCR Deactivation Mechanism

Zeolite

Durability

5 10 15 20 25 30 35 40 45

2 theta

6

SCR Deactivation Mechanism Understanding

Zeolite Structure

Cu Sites:

Found Cu sintering on engine aged samples, especially the gas inlet section.

Cu sintering seems to be controlled by gas phase chemistry rather than the aging temp.

Active Sites

Durability

7

SCR Deactivation Mechanism

Cu Sites

Fresh Cat B

Engine 120K 1st

inch Cat B

Basically same morphology as the fresh material

Very (!!) significant Cu sintering behavior evident (consistent with XRD and EPMA)

8

SCR Deactivation Mechanism Cu Sites

120K 1st

inchCat C

120K 7th inchCat C

Basically same morphology.No evidence of Cu sintering

on the 7th.Some minor portion shows Cu

sintering behavior on the 1st.

Cu sintering behavior

NOx Conversion, SV=30K, 350ppmNO/350ppm NH3

0

10

20

30

40

50

60

70

80

90

100

100 150 200 250 300 350 400 450 500 550 600Catalyst T, C

NO

x C

onve

rsio

n

NOx conv 100% NO B1-1(test1)

NOx conv 100% NO B1-7

9

Cu still located inside

not sintered on the external surface of the oxide particle

SCR Deactivation Mechanism

Cu SitesLab 860/30min (Cat A)

Serious Cu sintering after the NH3

TPD.

Aging at 700C under O2 atmosphere

no serious sintering.

Reduction with H2

flow

sintering started

10

SCR Deactivation Mechanism Understanding

Zeolite StructureActive Sites:

The overall activity is not high if the Al is not stable in the framework structure of zeolite

(dealumination).

Acidity of SCR catalysts reflects the status of active sites.

Not only the thermal factor, but also chemical

factors, such as reductants

and urea, impact the stability of active sites.

Durability

Cu Sites

11

SCR Deactivation Mechanism

Active Sites

It is known that surface acidity is important for ammonia SCR reaction.

Characterize the acidity through measuring adsorbed NH3 that associated to the acid sites on the catalysts. But, can not measure the types (Bronsted

or Lewis) of acid sites.

The overall acidity of SCR reflects its activity.

NOx Conversion, Engine 120K, Cat B

0102030405060708090

100

100 150 200 250 300 350 400 450 500 550 600Catalyst Temperature, C

Con

vers

ion,

%

NOx conv 100% NO 120K Eng. Aged 1-3NOx conv 100% NO 120K Eng. Aged 1-5NOx conv 100% NO 120K Eng. Aged 1-8

NH3 TPD, Engine 120K, Cat B

0

20

40

60

80

100

120

140

150 200 250 300 350 400 450Catalyst Temperature, C

NH

3, P

PM

120K Engine Aged, 1st120K Engine Aged, 3rd120K Engine Aged, 5th120K Engine Aged, 8th

12

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Rela

tive

loss

of t

etra

hedr

al A

l(a.u

.)1st 2nd+3rd 4th 5th 6th+7th 8th

304050607080

Chemical Shift(ppm)

1st2nd+3rd4th5th6th+7th8th

Subtraction from fresh: relative loss of Altet

SCR Deactivation Mechanism

Active Sites

The decreasing of acidity is not the only factor that causes the decreasing of SCR activity.

Relative loss of Altet

(Engine 120K, Cat B) from NMR data

13

-100-50050100150

Chemical shift(ppm)

Fresh

770oC 30min aged

770oC 30min wet urea

860oC 30min aged

47ppm

*

*

*: spinning side band

SCR Deactivation Mechanism

Active Sites

860 C 30 min aged sample: no evidence for tetrahedral aluminum which means decompose of zeolite structure.

770 C 30 min aged: no significant change from fresh sample.

770 C 30 min wet urea: less amount of tetrahedral aluminum which indicate some dealumination.

0102030405060708090

100

100 150 200 250 300 350 400 450 500 550 600Catalyst Temperature, C

Con

vers

ion,

%

NOx conv 100% NO FreshNOx conv 100% NO 860C 30minNOx conv 100% NO 770C 30minNOx conv 100% NO 770C 30min urea/wet

Solid state 27Al-NMR

14

Active Sites

Acidity and Relative Dealumination

304050607080

Chemical shift(ppm)

770C 30min770C wet urea860C 30 min

Relative DealuminationNH3 TPD, Cat A

0

50

100

150

200

250

150 200 250 300 350 400 450Catalyst Temperature, C

NH

3, P

PM

Degreened860C 30min770C 30min770C 30min urea/wet

Aging factors impact SCR acidity differently.

15

SUMMARY

The stability of zeolite

structure, Cu sites, and active

sites

all contribute to the durability of SCR catalysts. They are correlated with each other and equally important.

Dealumination, zeolite

structure damage, base metal sintering are the root causes of SCR deactivation.

Some aging conditions impact all three features, but some might just impact one or two or them.

There are lots of unknowns that need to be investigated

Zeolite

structure, Cu sites, and active sites each contribute

to the SCR catalyst durability.

Control of the aging factors to minimize the impact on Cu/zeolite

SCR catalysts in diesel applications.

16

ACKNOWLEDGEMENTS

Financial support for studies performed at Pacific Northwest National Laboratory (PNNL) was provided by the U.S. Department of Energy (DOE), Office of FreedomCar

and Vehicle Technologies.

Portions of the work were performed in the Environmental Molecular Sciences Laboratory (EMSL) at the PNNL. The EMSL is a national scientific user facility and supported by the U.S. DOE Office of Biological and Environmental Research.

Understanding the Deactivation Mechanisms of Cu/Zeolite SCR Catalysts in Diesel ApplicationIntroductionThe Durability of Cu/Zeolite SCR CatalystsZeolite Stability Thermal DeactivationSlide Number 5SCR Deactivation Mechanism UnderstandingSCR Deactivation Mechanism Cu SitesSCR Deactivation Mechanism Cu SitesSlide Number 9SCR Deactivation Mechanism UnderstandingSlide Number 11Slide Number 12SCR Deactivation Mechanism Active SitesActive Sites Acidity and Relative DealuminationSUMMARYACKNOWLEDGEMENTS