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Accelerated Aging of Fe-Zeolite SCR Catalysts: Engine and Bench-Flow Approaches. Prof. Ke Nguyen Mechanical, Aerospace and Biomedical Engineering University of Tennessee at Knoxville, USA Presented at HCM City University of Technology May 27, 2008. Acknowledgements.

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Accelerated Aging of Fe-Zeolite SCR Catalysts: Engine and Bench-Flow Approaches

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Accelerated aging of fe zeolite scr catalysts engine and bench flow approaches l.jpg

Accelerated Aging of Fe-Zeolite SCR Catalysts: Engine and Bench-Flow Approaches

Prof. Ke Nguyen

Mechanical, Aerospace and Biomedical Engineering

University of Tennessee at Knoxville, USA

Presented

at

HCM City University of Technology

May 27, 2008


Acknowledgements l.jpg

Acknowledgements

Research is supported by the U.S. Department of Energy (DOE), Office of FreedomCAR and Vehicle Technologies, Fuels Technology Program.

Fe-Zeolite SCR catalysts used were provided by Catalytic Solutions


Outline l.jpg

Outline

  • Engine-based aging and performance evaluation

  • Bench flow reactor-based performance evaluation of fresh and engine-aged Fe-Zeolite SCR catalysts

  • Results of surface characterization studies of fresh and engine-aged Fe-Zeolite SCR catalysts


High temperature thermal aging of fe zeolite scr catalysts l.jpg

High-Temperature Thermal Aging of Fe-Zeolite SCR Catalysts

  • Key concern for Fe-Zeolite SCR catalysts durability

    • High temperatures periodically required to regenerate DPFs

  • Expected deactivation mechanisms

    • Lube-oil poisoning

    • Contaminations from DOC

    • Changes in zeolite structure

    • Washcoat breakdown, i.e., crackings


Background of scr catalysts l.jpg

Background of SCR Catalysts

  • Metal oxide SCRcatalysts: V2O5 supported on either TiO2 or Al2O3

    - High NOx reduction ( ~90%)

    - Low temperature (350 - 450°C)

    - Lack of high-temperature durability

    - Emitting volatile vanadyl species

    - High catalyzing potential to oxidize SO2 to SO3

    SO3 reacts with NH3 to form ammonium sulfate

    and bisulfate: catalyst poisoning

  • Zeolite SCR catalysts: most common Cu and Fe-Zeolite

    - High NOx reduction (~90%) over large

    temperature range(300-600°C)

    - High temperature heavy-duty diesel applications

    - Low potential to oxidize SO2 to SO3

    - Cu-Zeolite produces more N2O than Fe-Zeolite

  • Focus only on Fe-Zeolite SCR catalysts


Scr reactions between nh 3 and no x l.jpg

SCR Reactions Between NH3 and NOx

  • Major reactions in the SCR process :

    4NH3 + 4NO + O2 4N2 + 6H20(1)

    4NH3 + 2NO + 2NO2 4N2 + 6H20 (2)

    4NH3 + 3NO2 3.5N2 + 6H20 (3)

  • Reaction 2 is the fastest reaction

  • Reaction 1 is the intermediate reaction

  • Reaction 3 is the slowest reaction


Scr of no x by nh 3 l.jpg

SCR of NOx by NH3

Alpha (α) is defined as the ratio of NH3 to NOx

Exhaust gases consist mainly of NO (~90%), an α of 1 is required to reduce NOx (reaction 1)

In most systems some NO is oxidized to NO2 with a DOC to increase the ratio NO2:NO in exhaust gases

SCR generally proceeds according to reaction 2

NO2/NO must not be greater than 1, since reaction 3 is slowest

NH3 can be solely introduced to the exhaust gases without prior oxidation of NO to NO2


Engine based aging l.jpg

Engine-Based Aging


Schematic of engine aftertreatment fe zeolite scr catalysts evaluated as system with doc and dpf l.jpg

Schematic of Engine AftertreatmentFe-Zeolite SCR catalysts evaluated as system with DOC and DPF


Specifications of aftertreatment system l.jpg

Specifications of Aftertreatment System

DOC Exit gas

SCR Exit Gas

DOC

Mixer

SCR

DPF

Cat Out

Cat In

DPF Exit gas

DOC Inlet gas

SCR Inlet gas

DPF T1


Engine bench setup located at ntrc l.jpg

Engine Bench Setup Located at NTRC

Exhaust

Sampling

SCR Catalysts

Exhaust Fuel

Injection

Drive Motor

500cc Hatz

Engine

Syringe Pump

Throttle

Controller


Engine based aging and evaluation l.jpg

Engine-Based Aging and Evaluation

  • Engine operates steady state at 1500 rpm

    • ~800 ppm NOx, exhaust temperature ~350°C, GHSV = 60000 h-1

  • SCR catalysts are aged by raising exhaust gas temperature during active DPF regeneration

    • Supplemental fuel is injected into the exhaust upstream of the DOC

  • Aging cycles

    • Up to 50 aging cycles of 25 minutes each

    • Atomized fuel is injected in five-minute increments until exhaust temperatures of 600, 750 and 850°C are achieved then cut off fuel

      • Desired exhaust temperatures are obtained at fuel cut-off

  • Evaluation cycles

    • Evaluation is carried out after a given number of aging cycles at an exhaust temperature of ~350°C

    • Inject 5% of NH3 in N2mixture such that α = NH3/NO = 0.6 to minimize NH3 slip


Slide13 l.jpg

SCR Catalysts Used in Engine Bench Fe-Zeolite SCR catalysts of 400 cpsi and cordierite substrate mainly used for heavy-duty diesel applications are provided by Catalytic Solutions

7.6 cm

15.2 cm


Sem micrographs of fresh fe zeolite scr catalyst l.jpg

SEM Micrographs of Fresh Fe-Zeolite SCR Catalyst

• Channels shown are uniform

• Washcoat thickness varies


Slide15 l.jpg

Energy Dispersive Spectroscopy (EDS) of Fresh Fe-Zeolite SCR Catalyst

•EDS performed on washcoat corner of few atomic layer

•Al, Si, O, Fe, Ce, Zr and Au peaks detected

•Al, Si, O and Fe are components of zeolite

•Ce and Zr are components of oxygen storage materials

•Au peak is from gold coating applied to the sample before performing SEM


Typical temperature profiles during scr catalyst aging on engine bench at 650 c 0 6 l.jpg

Typical temperature profiles during SCR catalyst aging on engine bench at 650°C(α = 0.6)

•Repeatable temperature profile during aging

• Axial temperature variation in SCR catalyst

•SCR catalyst inlet experiences higher temperature than exit (~90°C)


Slide17 l.jpg

NOx emissions during SCR catalyst aging on engine bench at 650°C (α = 0.6)

•Cycle to cycle variation of NOx emissions during aging

•Half of NO is oxidized to NO2 by DOC and DPF

•During engine evaluation less than half of NOx out is NO

•NOx conversion of ~50% is obtained with α = 0.6

Cat In NO and NOx (no NH3)

Cat Out NOx (with NH3)

Cat Out NO (no NH3)

Cat Out NO (with NH3)


Typical temperature profiles during scr catalyst aging on engine bench at 750 c 0 6 l.jpg

Typical temperature profiles during SCR catalyst aging on engine bench at 750°C (α = 0.6)

• Temperature

profile is

repeatable

• Axial

temperature

variation in

SCR catalyst

• Front section of

SCR catalyst

experiences

higher

temperature than

rear section

(~100°C)


Slide19 l.jpg

NOx emissions during SCR catalyst aging on the engine bench at 750°C

Cat In NO and NOx (no NH3)

Cat Out NOx (with NH3)

  • Cycle to cycle variation of NOx emissions during aging

  • NOx conversion evaluated with α = 0.6

Cat Out NO (no NH3)

Cat Out NO (with NH3)


Typical temperature profiles during scr catalyst aging on engine bench at 850 c 0 6 l.jpg

Typical temperature profiles during SCR catalyst aging on engine bench at 850ºC (α = 0.6)

•Repeatable temperature profile

•Axial temperature variation along SCR catalyst

•Smaller temperature difference between SCR inlet and exit (~ 40°C)


No x emissions during scr catalyst aging on engine bench at 850 c l.jpg

NOx emissions during SCR catalyst aging on engine bench at 850°C

Cat In NO and NOx (no NH3)

Cat Out NOx (with NH3)

•Cycle to cycle variation of NOx emissions during aging

•NOx conversion evaluated with α = 0.6

Cat Out NO (no NH3)

Cat Out NO (with NH3)


Bench flow reactor performance evaluation l.jpg

Bench-Flow Reactor Performance Evaluation


Bench flow reactor evaluation l.jpg

Bench-Flow Reactor Evaluation

  • Bench reactor evaluation of fresh and engine-aged Fe-Zeolite SCR catalysts

    • Temperature varied between 200 and 600°C

    • α varied between 0.5 and 1.2

  • Surface characterization studies

    • SEM-EDS, EPMA, XRD and BET


Slide24 l.jpg

Performance Evaluation of Fresh and Engine-Aged SCR Catalysts is Carried Out on Bench-Flow Reactor

SCR Catalyst Reactor


Slide25 l.jpg

Fe-Zeolite SCR Catalysts -Fresh Fe-Zeolite SCR catalysts-Engine-aged Fe-Zeolite catalysts • Two cored samples are obtained from engine-aged catalysts: front half and rear half • Evaluation is performed separately on both engine-age samples

22 mm

75 mm


Slide26 l.jpg

Thermocouple locations in SCR catalyst

57mm

38mm

Flow

5mm

5mm

75.5mm

19mm


Composition of simulated exhaust gases l.jpg

Composition of Simulated Exhaust Gases

NOx performance evaluations areperformed at

GHSV of 30,000 h-1


Typical scr catalyst temperature at different locations during evaluation at 500 c ghsv 30 000 h 1 l.jpg

Typical SCRcatalyst temperature at different locations during evaluation at 500ºC, GHSV = 30,000 h-1

• Steady state

temperatures

obtained during

evaluation

• ∆Tmax=19°C


Nox conversion of fresh fe zeolite scr catalysts with 350 ppm no at ghsv of 30 000 h 1 l.jpg

NOx conversion of fresh Fe-Zeolite SCR catalysts with 350 ppm NO at GHSV of 30,000 h-1

•Maximum NOx conversion of 94% occurs at 400ºC at α = 1.2

•NOx conversion increases with α

•Lower NOx conversion at T>500°C due to oxidation of NH3

•Low NOx conversion at 200°C due to kinetics


No x conversion of engine aged fe zeolite scr catalysts 1 l.jpg

NOx Conversion of Engine-Aged Fe-Zeolite SCR Catalysts (α=1)

•Front section of both engine-aged catalysts degraded severely

•Reduction in NOx performance in front-half is possibly due to lube-oil poisoning, contaminations from DOC and cracking of washcoat

•Catalyst aged at 650°C is being evaluated


Slide31 l.jpg

XRD patterns of fresh and aged Fe-Zeolite SCR Catalysts

∆ - CexZr1-xO2

◊ - ZrO2

□ - Zeolite

○ - CeO2

● - Cordierite

† - Fe2O3

♠ - Al2O3

♦ - Si

•Significantly less zeolite detected in aged samples

•Fe2O3 and Al2O3 peaks are discernable in aged samples

•Zeolite structure begins to breakdown around 800°C for many high-silica zeolites

64 hrs on BFR (28ppm SO2)

13 cycles at 850°C (Front)

13 cycles at 850°C (Rear)

Fresh Fe-SCR


Expanded xrd patterns of fresh and engine aged fe zeolite scr catalysts l.jpg

Expanded XRD patterns of fresh and engine-aged Fe-Zeolite SCR catalysts

Zeolite

--------Fresh

-------- 800°C


Bet surface area measurements of fresh and engine aged fe zeolite scr catalysts l.jpg

BET surface area measurements of fresh and engine-aged Fe-Zeolite SCR catalysts

•Surface area includes zeolite and cordierite substrate

•Front sections of engine-aged SCR catalysts experience severe loss of surface area

•Surface area is higher if cordierite substrate is excluded

•Surface area reduction correlates with aging temperature


Epma elemental maps of fresh fe zeolite scr catalyst l.jpg

EPMA elemental maps of fresh Fe-Zeolite SCR catalyst

Zn

P

• Fe is well-dispersed

in washcoat

• ZrO2 and CeO2 are

the oxygen storage

materials

• Si is one of constituent

of zeolite

• Trace of P is detected

S

Ca

Fe

Si

Zr

Ce


Epma elemental maps of fe scr catalyst aged for 31 cycles at 650 c front l.jpg

EPMA elemental maps of Fe-SCR catalyst aged for 31 cycles at 650°C (front)

P

Pt

• Fe is still well dispersed

in washcoat

• Agglomeration of ZrO2

and CeO2

• More P is detected in

front due to lube-oil

contamination

• Trace of Pt is detected

S

Ca

Fe

Si

Zr

Ce


Epma elemental maps of fe zeolite scr catalyst engine aged for 31 cycles at 650 c rear l.jpg

EPMA elemental maps of Fe-Zeolite SCR catalyst engine-aged for 31 cycles at 650°C (rear)

P

Pt

•Fe is well-dispersed in washcoat

•Trace of Pt is detected

•Agglomeration of ZrO2 and CeO2

• Less P deposited

in rear section

S

Ca

Fe

Si

Zr

Ce


Epma elemental maps of fe zeolite scr catalyst engine aged for 50 cycles at 750 c front l.jpg

EPMA elemental maps of Fe-Zeolite SCR catalyst engine-aged for 50 cycles at 750°C (front)

P

Pt

• Cracking of washcoat

is visible in front

section due to higher

temperature

• Contamination from

lube oil, i.e., P

Ca

S

Fe

Si

Zr

Ce


Epma elemental maps of fe zeolite scr catalyst engine aged for 50 cycles at 750 c rear l.jpg

EPMA elemental maps of Fe-Zeolite SCR catalyst engine- aged for 50 cycles at 750°C (rear)

P

Pt

•Temperature in rear-half is much less than 750C

•No cracking of washcoat is observed in rear-half, which explains higher NOx conversion

•Only trace of Pt is detected

Ca

S

Fe

Si

Zr

Ce


Epma elemental maps of fe zeolitescr catalyst engine aged for 13 cycles at 850 c front l.jpg

EPMA elemental maps of Fe-ZeoliteSCR catalyst engine-aged for 13 cycles at 850°C (front)

P

Zn

• Severe crackings of

washcoat

Ca

S

Fe

Si

Zr

Ce


Epma elemental maps of fe scr engine aged for 13 cycles at 850 c rear l.jpg

EPMA elemental maps of Fe-SCR engine-aged for 13 cycles at 850°C (rear)

P

Zn

•Severe cracking of washcoat

Ca

S

Fe

Si

Zr

Ce


Conclusions l.jpg

Conclusions

  • Loss of NOx performance of engine-aged Fe-Zeolite SCR catalysts is mainly due to:

    - Loss of surface area (BET)

    - Breakdown of zeolite structure at temperatures above 800°C (XRD)

    • Severe cracking of washcoat at temperatures above 750°C (EPMA)

    • Agglomeration ofCeO2 and ZrO2

    • Contamination from lube-oil


Thank you l.jpg

Thank You

Questions ????


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