mqshen ceria-based materials in automotive catalysis

8/14/2019 mqshen Ceria-Based Materials in Automotive Catalysis

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Studies of Ceria-based Materials in

Automotive Exhaust Control Catalysis

Meiqing Shen

[email protected] School of Chemical Engineering and Technology,Tianjin University

CHINA-US Workshop 2009
mailto:[email protected]:[email protected]


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Automotive Catalysis at Stoichiometric and Lean conditions

Emission limit raised by engine and catalysts optimization.

Besides TWC, novel catalysts required for lean-burn exhaust control.

Oxidation catalysts

Selective Catalytic Reduction

NO x Storage Reduction

HC+CO+PM+NO x

*Gandhi H S et al . Journal of Catalysis, 2003, 216, 433.* Burch R. Catalysis Reviews, 2004, 46, 271.

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Ceria-based Materials in Automotive Catalysts

Rare-earth materials can be utilized in automotive catalysts withmultiple functions Challenges:

Mechanisms of specific catalytic process;Know-how materials design and synthesis;Sustainable high activity;Systematic approach to the development of after-treatmentTWC

LNT/ SCR

Gasoline Engine

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Oxygen Storage Capacity;

Enhancement for WGS and SR;

Disperse and activate active sites;

Modifications of Ceria-based materials

Ceria Catalysis

' ..

2

12 2

2

x

Ce O Ce OCe O Ce V O+ + +

0 100 200 300 400 500 600

0

20

40

60

80

100

0

20

40

60

80

100

C 3 H 8 C o n v e

r s i o n ( % )

C O C o n v e

r s i o n ( % )

Temperature ( oC)

(a)

*Kapar J et al . Catalysis Today, 2003, 77(4),419. 4


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Controllable Synthesis of Ceria-zirconia Solid Solutions

Synthesizing nanospherical CeO 2-ZrO 2 by two-phase approach

The TEM image of Ce 0.7Zr0.3O2 after calcination at 300 C for 4h in air.

Homogeneous bulk phases and meso-poresize distributions after calcination at 300 C for 4h in air.

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Studies of Dynamic Reactions

Developing cycling pulse tests for kinetics study and real practice

0 5 10 15 20

C o n c e n t r a t

i o n ( a . u )

CO2(1)

CO2(2)

CO 2 outlet

O2 outlet

CO outlet

O2 inlet

CO inlet

Time(s)

Flow chart of dynamic OSC measurement.

CO, O 2 and CO 2 responding curves in dynamic OSC measurement.

CO-O 2 pulses pass through catalysts bed almost asplug flows (catalysts are mixed with quartz sand).

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Experimental Studies on Oxygen Mobility

Developing cycling pulse tests for kinetics study and real practice

In-situ EPR/ DRIFTS: Local environment around O 2 -

Isotopic exchange: Oxygen storage/release mechanism

Superoxides

Flow chart of the combined vacuum system for thein-situ analysis of oxygen species.

Schematic system of the isotopic exchange .

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Simulation Studies on Lattice Oxygen Mobility

Substitute site of Ni Interstitial site of Ni

Ni-doping enhances the O buffering effect of ceria;Substitutional system: O vacancy formation in the leads to thereduction of Ni atoms;

Insterstitial system: Reduction of the determines the reduction oftwo Ce atoms.

Oxygen vacancies and Ce 4f electrons

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O Backspillover Controlled Oxidation Capability

Different states of Pd can be observedon oxidized (A) and reduced (B) CZ

Increasing gap of activation energies fordeep oxidation by Pd catalysts

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Oxidation Capability Determined by Lattice Oxygen

Lean Rich

Temperature/ReducibilityDependence

OxygenVacancyDependence

OSC activity of Pd supported samples atincreasing temperatures.

EPR Ce 3+ related signal of CZ samples.10


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Modified Reaction Networks

Competitions of different reactions

Evolution of gases along the catalysts bed in dynamic reactions

WGS and SRcompete witheach otheralong theincreasingtemperatures

WGS SR

Evolution of multiple gases (left) and surface adsorbates on catalysts (right) in the complete lean-rich cycles. 12


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Ceria related interactions with main active sites

Ceria related interactions with promoters and support oxides

Interactions among Standard Components

Ceria issensitive to

agingatmospherein modifyingcomponentsdistributions

HA-SA

Pd/HA-Pd/SA

Pd/SA-Pd/SAA

Effect of ceriain hinderingPGM sinteringis essential

10 % H 2Ohydrothermal

aging at 1073 K

10 % H 2O +10 %CO

2hydrothermal

aging at 1073 K 13


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Dopants Induced Interactions

Effects of dopants (Fe) for ceria lattice (Rietveld Analysis)

Effects of dopants (Sr) for catalytic activity at varying A/F windows0.00 0.02 0.04 0.06 0.08

5.406

5.408

5.410

5.412

[Fe]/[(Fe)+(Ce)] (%)

L a t t i c e

C o n s t a n

t

0.00 0.02 0.04 0.06 0.084

8

12

16

20

24

[Fe]/[(Fe)+(Ce)] (%)

O x y g e n v a c a n c y

( % )

Solubility ofdopants controlslatticerelaxation

Effects ofdopants for CO,HCs and NO xconversion maynot always go inthe samedirection 14


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Optimizations of the Catalysts Formulations

Ceria-alumina support oxides with different mixing ways

CZAMO-M CZAMO-P CZAMO-A

CZ

A

32 '

22 2 3 Al

Ce o oCeO Al V O

+

+ +

Activation energies of CO oxidations.

Al3+

VOCe4+

O2-

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Optimizations of the Catalysts Formulations

Ceria-barium-aluminawith stepwise changingcore-shell distributions

StorageComponents

Promoter Supportoxides

Texture

Chemistry

Performance

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Sustainable Activity of Ceria-based Catalysts

FeCrAl foils and washcoat on -alumina based ceramic materials (left), and the change of E10catalystsmorphology along the radial wall of monolith after being used.

500 ppm NO, 7.5 % O 2, GHSV: 30,000 h-1, 800 , 12 h hydrothermal + 10 % CO 2 aging.

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Summary and Final Words

O transfer ability in ceria (or other RE elements) lattice is essentialfor the activity of automotive catalysts, but different catalysis and

technical issues appear in different situations

Kinetics study of O mobility based on the precise measurement of

active sites needs further addressing

Novel catalysts with nanostructured design and synthesis are

demanded for the study of fundamental issues and the

development of advanced material

A system approach is required to develop and optimize

aftertreament catalysis technologies ( Materials, Reactions, and

Simulations )18


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Related Recent Publications

1. Yang M, Shen M, Wang J at al . Pd-Support interaction defined selective redox activities in Pd Ce 0.7Zr0.3O2Al2O3 model

three-way catalysts. Journal of Physical Chemistry C ,2009

, 113, 12778-12789.2. Shen M, Yang M, Wang J et al . Pd/support interface-promoted Pd Ce 0.7Zr0.3 O2Al2O3 automobile three-way catalysts:

studying the dynamic oxygen storage capacity and CO, C 3H8, and NO conversion. Journal of Physical Chemistry C , 2009 ,113(8) 3212-3221.

3. Shen M, Wang J, Shang J et al . Modification ceria-zirconia mixed oxides by doping Sr using the reversed microemulsion forimproved Pd-Only three-way catalytic performance. Journal of Physical Chemistry C , 2009 , 113(4): 1543-1551.

4. Wang Y, Wang J, Shen M et al . Synthesis and properties of thermostable -alumina prepared by hydrolysis of phosphidealuminum. Journal of Alloys and Compounds , 2009 , 467(1-2): 405-412.

5. Wang J, Wen J, Shen M. Effect of interaction between Ce 0.7 Zr0.3O2 and Al 2O3 on structural characteristics, thermal stability,and oxygen storage capacity. Journal of Physical Chemistry C 2008 , 112(13): 5113-5122.6. Jia L, Shen M, Hao J et al . Dynamic oxygen storage and release over Mn 0.1Ce0.9 Ox and Mn 0.1Ce0.6 Zr0.3Ox complex

compounds and structural characterization. Journal of Alloys and Compounds , 2008 , 454(1-2): 321-326.7. Zhao M, Shen M, Wen X et al . CeZrSr ternary mixed oxides structural characteristics and oxygen storage capacity.

Journal of Alloys and Compounds , 2008 , 457(1-2): 578-586.8. Jia L, Shen M, Hao J et al . Dynamic oxygen storage and release over Mn 0.1Ce0.9 Ox and Mn 0.1Ce0.6 Zr0.3Ox complex

compounds and structural characterization. Journal of Alloys and Compounds , 2008 , 454(1-2): 321-326.

9. Zhao M, Shen M, Wang J et al . Influence of Pd morphology and support surface area on redox ability of Pd/Ce 0.67 Zr0.33 O2under CO-He pulse and transient CO-O 2 measurements. Industrial & Engineering Chemistry Research , 2007 , 46(24): 7883-7890.

10. Jia L, Shen M, Wang J. Preparation and characterization of dip-coated -alumina based ceramic materials on FeCrAl foils.Surface & Coatings Technology , 2007 , 201(16-17): 7159-7165.

11. Zhao M, Shen M, Wang J. Effect of surface area and bulk structure on oxygen storage capacity of Ce 0.67 Zr0.33 O2. Journal of Catalysis , 2007 , 248(2): 258-267.

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Acknowledgements

Collaborators:

Natural Science Foundation of China;BASF Catalysts LLC, USA;General Motors R&D Center, USA;CNR-INFM DEMOCRITOS National Simulation Center, Italy

Current Students:Xinquan WangJianqiang WangYuewei ZhangJing WenMing YangAnju ShiChao LeiJiahao Chen

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mqshen ceria-based materials in automotive catalysis

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