Perform

a

nce C

h

aracterization of C

u/Zeolite a

n

d

Fe/Zeolite C

atalysts

for the Selective C

atalytic Red

uction of N

O

x

Giovanni Cavataio, James Girard, Joseph Patterson, Clifford Montreuil,

Yisun Cheng, and Christine Lambert

Ford Motor Company, Research and Innovation Center

2101 Village Road, Dearborn, MI 48124 USA

Introduction

Reduction of nitrogen oxides (N

Ox) in the lean exhaust gas of diesel engines is not

trivial. The well-known reaction chemistry of a typical precious metal three-way catalyst

(T

W

C) is not effective for N

Ox conversion in lean exhaust. Urea-based Selective Catalytic

Reduction (SC

R) has the potential to meet U.S. Diesel Tier 2 Bin 5 emission standards for

N

Ox in 2010 [1]. The reduction of N

Ox with either am

monia (N

H3) or urea has been used

extensively for stationary source emission control. N

Ox reduction is possible due to the high

selectivity of the N

H3 and N

Ox reaction to form elemental N2. Urea decomposes to N

H3

following a well-known two-step decomposition process involving thermolysis and hydrolysis.

The U.S. Tier 2 Bin 5 N

Ox standard represents a challenging 90+% reduction from previous

standards. The varying operating and driving conditions of light-duty and heavy-duty vehicles

make it necessary to customize catalyst features to the application. Generally, light-duty

applications require SC

R catalysts to function well at low temperatures (<350°C) whereas

heavy-duty applications require functionality at higher temperature (>350°C) and high space

velocity. One major thermal durability requirement of SC

R formulations involves

withstanding the high temperature process of regenerating particulate filters from accumulated

soot. On the basis of performance, three important parameters for the selecting the proper SC

R

formulation involves the exhaust temperature profile, the N

O2/N

Ox ratio, and the amount of

N

H3 stored on the catalyst surface. In addition to thermal durability, this paper reviews a

detailed comparison between the basic catalytic activity of Cu/Zeolite and Fe/Zeolite

formulations, and their resistance to poisons such as sulfur and hydrocarbons.

Materials and Methods

Fundamental catalyst activity data were obtained using a laboratory-scale flow

reactor system. A round sample core of 1" diameter by 1" long was taken from a washcoatedCu/Zeolite and Fe/Zeolite monolith obtained from a supplier. The catalyst temperature was

maintained with a tube furnace. Simulated diesel exhaust gas was flowed through the sample

core consisting of 350ppm

N

Ox, 350ppm

N

H3, 14%

O2, 5%

H2O, 5%

C

O2, and balance N2.

The total gas flow rate was 6.44 liters per minutes resulting in a gas hourly space velocity(G

HSV) equal to 30,000/hr. A

Nicolet FTIR instrument with a heat sample cell was used at

the outlet of the reactor to measure N

O, N

O2, N2O, N

H3, H2O, and C

O2 concentrations. Before

evaluation, all catalysts were hydrothermally aged at 670°C for 64 hours in the presence of 5%

H2O, 14%

O2, 5%

C

O2, and balance N2.

Results and Discussion

Performance plots in Figure 1 show the active temperature range for Cu, Fe, and

vanadium based SC

R catalysts, the impact from high temperature 1 hour aging, the influence

of stored N

H3 on low temperature activity, and the N

Ox conversion sensitivity to exhaust N

O2

fraction. The following main conclusions emerge from this s

formulations were found to be more thermally stable than va

never-to-exceed temperature for Cu/Zeolite was established to 

was higher (925°C), c) N

Ox conversion for both Cu and Fe/Z

functions of N

H3 storage capacity, d) low temperature N

Ox 

and Fe/Zeolite was improved with the increase in N

O2 fractio

was more sensitive to the N

O2/N

Ox ratio.

Figure 1. a) N

Ox conversion over Cu, Fe, and Vanadiu

Cu/Zeolite N

Ox conversion after 1 hour aging from 750°

conversion as function of exposed N

H3, d) Cu/Zeolite N

Ox c

Note: SC

R catalysts aged at 670°C for 64 hours in a) – d).

Significance

The transient driving nature of light-duty and heavy-duty 

understand the key SC

R functions and durability limit

conditions. Results in this study highlight main differences b

SC

R formulations and provides insight into key parameters im

References

1. Christine K. Lambert, Paul M. Liang, and Robert H. Ham

Aftertreatment Models to Guide System

Design for Tier I

2002-01-1868.

0

102030405060708090

100

100 150 20

NOx Conversion (%)

750°C

0

102030405060708090

100

100 150 2

NOx Conversion (%)

0

102030405060708090

100

100 150 200 250 300 350 400 450 500 550 600

Inlet Gas Temperature (oC)

NOx Conversion (%)

Cu/Zeolite SCRFe/Zeolite SCRVanadium Based SCR

0

102030405060708090

100

100 150 200 250 300 350 400 450 500 550 600

Inlet Gas Temperature (oC)

NOx Conversion (%)

Steady State1.00g/L NH30.75g/L NH30.50g/L NH30.25g/L NH30.10g/L NH3

a) b)

c) d)