Mqshen Ceria-based Materials In Automotive Catalysis

CHINA-US Workshop’ 2009

Studies of Ceria-based Materials in Automotive Exhaust Control Catalysis

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

Automotive Catalysis at Stoichiometric and Lean conditions Oxidation catalysts

Selective Catalytic Reduction

HC+CO+PM+NOx Emission limit raised by engine and catalysts optimization.

NOx Storage Reduction

Besides TWC, novel catalysts required for lean-burn exhaust control. *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 with multiple functions Challenges:

Mechanisms of specific catalytic process; Know-how materials’ design and synthesis; Sustainable high activity; TWC Systematic approach to the development of after-treatment LNT/ SCR Gasoline Engine

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Ceria Catalysis Oxygen Storage Capacity;

1 O2 2

Enhancement for WGS and SR;

(a)

CO Conversion (%)

100

100

80

80

60

60

40

40

20

20

0

0 0

100

200 300 400 Temperature (oC)

500

C3H8 Conversion (%)

x ' 2CeCe + OO ↔ 2CeCe + VO.. +

600

Disperse and activate active sites; Modifications of Ceria-based materials

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

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Controllable Synthesis of Ceria-zirconia Solid Solutions Synthesizing nanospherical CeO2-ZrO2 by two-phase approach

The TEM image of Ce0.7Zr0.3O2 after calcination at 300 ºC for 4h in air.

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

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Studies of Dynamic Reactions Developing cycling pulse tests for kinetics study and real practice

Flow chart of dynamic OSC measurement. CO inlet

Concentration(a.u)

CO outlet CO2(1)

O2 inlet CO2 outlet

CO2(2)

0

5

10

CO-O2 pulses pass through catalysts’ bed almost as plug flows (catalysts are mixed with quartz sand).

O2 outlet

15

20

Time(s)

CO, O2 and CO2 responding curves in dynamic OSC measurement.

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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 O2-

Superoxides

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

Isotopic exchange: Oxygen storage/release mechanism

Schematic system of the isotopic exchange .

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Simulation Studies on Lattice Oxygen Mobility Oxygen vacancies and Ce 4f electrons

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 the reduction of Ni atoms; Insterstitial system: Reduction of the determines the reduction of two Ce atoms. 8

O Backspillover Controlled Oxidation Capability Different states of Pd can be observed on oxidized (A) and reduced (B) CZ

Increasing gap of activation energies for deep oxidation by Pd catalysts

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Oxidation Capability Determined by Lattice Oxygen

Lean

Temperature/ Reducibility Dependence OSC activity of Pd supported samples at increasing temperatures.

Rich

Oxygen Vacancy Dependence EPR Ce3+ related signal of CZ samples.

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O Transfer Controlled Selective Redox Activities

NOx conversion shows negative order to OSC performance.

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Modified Reaction Networks Competitions of different reactions WGS

SR

WGS and SR compete with each other along the increasing temperatures …

Evolution of gases along the catalysts bed in dynamic reactions

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

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Interactions among Standard Components Ceria related interactions with main active sites HA-SA

Pd/SA-Pd/SAA

Pd/HA-Pd/SA

Effect of ceria in hindering PGM sintering is essential… 10 % H2O hydrothermal aging at 1073 K

Ceria related interactions with promoters and support oxides Ceria is sensitive to aging atmosphere in modifying components distributions 10 % H2O +10 % CO2 hydrothermal aging at 1073 K

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Dopants Induced Interactions Oxygen vacancy (%)

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

5.412 5.410 5.408 5.406 0.00

0.02

0.04

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

0.06

0.08

24 20

Solubility of dopants controls lattice relaxation…

16 12 8 4 0.00

0.02

0.04

0.06

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

0.08

Effects of dopants (Sr) for catalytic activity at varying A/F windows

Effects of dopants for CO, HCs and NOx conversion may not always go in the same direction… 14

Optimizations of the Catalysts Formulations Ceria-alumina support oxides with different mixing ways

CZAMO-A

CZAMO-P

2 Al 3+

CZAMO-M

' → 2 AlCe + Vo•• + 3Oo× 2CeO2 ←

CZ A

Al3+ Ce4+

VO

O2-

Activation energies of CO oxidations.

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Optimizations of the Catalysts Formulations Ceria-barium-alumina with stepwise changing core-shell distributions Texture

Chemistry

Performance

Storage Components

Promoter

Support oxides

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Sustainable Activity of Ceria-based Catalysts

500 ppm NO, 7.5 % O2, GHSV: 30,000 h-1, 800 ℃, 12 h hydrothermal + 10 % CO2 aging.

FeCrAl foils and washcoat on γ-alumina based ceramic materials (left), and the change of E10catalysts morphology along the radial wall of monolith after being used.

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Summary and Final Words O transfer ability in ceria (or other RE elements) lattice is essential for 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

Related Recent Publications 1. Yang M, Shen M, Wang J at al. Pd-Support interaction defined selective redox activities in Pd−Ce0.7Zr0.3O2−Al2O3 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−Ce0.7Zr0.3O2−Al2O3 automobile three-way catalysts: studying the dynamic oxygen storage capacity and CO, C3H8, 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 for improved 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 γ-alumina prepared by hydrolysis of phosphide aluminum. Journal of Alloys and Compounds, 2009, 467(1-2): 405-412. 5. Wang J, Wen J, Shen M. Effect of interaction between Ce0.7Zr0.3O2 and Al2O3 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 Mn0.1Ce0.9Ox and Mn0.1Ce0.6 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. Ce–Zr–Sr 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 Mn0.1Ce0.9Ox and Mn0.1Ce0.6 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/Ce0.67Zr0.33O2 under CO-He pulse and transient CO-O2 measurements. Industrial & Engineering Chemistry Research, 2007, 46(24): 78837890. 10. Jia L, Shen M, Wang J. Preparation and characterization of dip-coated γ-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 Ce0.67Zr0.33O2. 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 Wang Jianqiang Wang Yuewei Zhang Jing Wen Ming Yang Anju Shi Chao Lei Jiahao Chen 20