, Yongwoo Kim , Sungha Hwang , Chang Hwan Kim *[email protected] · 2018-10-08 · 1School of Chemical...

1School of Chemical and Biological Engineering, Seoul National University2Hyundai-Kia R&D center, Rep. of Korea

Jaeha Lee1, YoungSeok Ryou1, Yongwoo Kim1, Sungha Hwang1,Hyokyung Lee2, Chang Hwan Kim2

Do Heui Kim1*

*[email protected]

2

2

Emissions during cold start

Exhaust gas during cold start (100sec)

More stringent regulations on emissions including RDE are forthcoming.

Depending on the driving condition and the evaluation method, the amount of NOx emitted during the cold start period could be up to ~40%.

3

PNA: Low temperature NO adsorption + DOC

Passive NOx Adsorbers (PNA)

cDPFDOC SCR

Engine NOx

During cold start

w/o PNA

cDPFPNA SCR

Engine NOx

w/ PNA

During cold startAfter warm up (> 200 °C)

N2

4

PNA or CSC: DOC + Low temperature NO adsorption

Cold start concept (CSCTM): a novel catalyst for cold start emission controlChen et al., SAE Int. J. Fuels Lubr. Volume 6, Issue 2(June 2013)

Cold start catalyst and its use in exhaust systemsChen et al., US patent, 2012/0308439 A1

Fundamental understanding of NO adsorption/desorption over Pd/CeO2 and Pd/zeolite catalysts

Pd/Ce-based oxide and Pd/zeolite

5

Part 1. PNA ability of Pd/CeO2

Part 2. PNA ability of Pd/SSZ-13(How to activate the PNA ability of Pd/SSZ-13?)

Part 3. Activation: Effect of hydrothermal conditions

Part 4. Deactivation by reducing treatments: CO and H2

Scope

6





Contents

7

Mark Crocker, et al. CeO2-M2O3 Passive NOxAdsorbers for Cold Start Applications. Emission Control Science and Technology, 2017, 3(1), 59-72

Doping ceria with Pr increased the NO adsorption ability. ((a) and (b))

However, the hydrothermal aging deactivated the catalysts((c)).

(BET surface area was severely decreased from ~70 to ~20 m2/g)

(a) (b)

PGMs on Ce-Zr oxide as PNA ?

HTA

(c)

8

Catalyst Preparation and Characterization Methods

Preparation of catalysts (PGM/CeO2)

Pt-Pd (2:0, 1:1, and 0:2 wt%): Incipient wetness impregnation method

Support: CeO2

Calcination: 500 °C for 2h with 15% O2 in N2

Hydrothermal Aging (HTA): 750 °C for 25h with 15% O2 and 10% H2O in N2

Activity measurement and characterization techniques

• NO adsorption/desorption: PNA ability of catalysts• Sulfur poisoning and regeneration• XRD: Structural and textural property of catalyst• H2-TPR: Reducibility of catalysts• DRIFT: Adsorbed species and their desorption behavior

9

Activity measurement: NOx adsorption/desorption

9.5% O2, 5% H2O, 5% CO2

9.5% O2, 5% H2O, 5% CO2, 100ppm NOx (85 ppm of NO and 15 ppm of NO2)

Reaction condition Catalyst

0.1 g of Pd/CeO2α-Al2O3 bead: 0.1 g

Flow rate: 200 sccm

(SV: 120,000 h-1)

𝑵𝑶𝒙 𝒔𝒕𝒐𝒓𝒂𝒈𝒆 𝒆𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 (𝑵𝑺𝑬) =𝑻𝒉𝒆 𝒂𝒎𝒐𝒖𝒏𝒕 𝒐𝒇 𝑵𝑶𝒙 𝒂𝒅𝒔𝒐𝒓𝒃𝒆𝒅

𝑻𝒉𝒆 𝒂𝒎𝒐𝒖𝒏𝒕 𝒐𝒇 𝑵𝑶𝒙 𝒊𝒏𝒕𝒓𝒐𝒅𝒖𝒄𝒆𝒅

10

Activity measurement: NOx adsorption/desorption

11

10 20 30 40 50 60

a.u

2(o)

(111)

(200)(220) (311)

500C samples

Pt/CeO2

Pt-Pd/CeO2

Pd/CeO2

Structural property of PGM/CeO2

7.8 nm

7.8 nm

7.8 nm

No PGM peaks → PGMs are highly dispersed on ceria.

The crystalline size of CeO2 slightly increased after HTA.

(BET surface area of Pd/CeO2 HTA is 86 m2/g)

10.7 nm

11.9 nm

10.7 nm

10 20 30 40 50 60

2 (o)

(111)

(200)(220)

(311)

HTA samples

XRD patterns

12

Effect of PGM and support

No low temperature peak over Pt containing samples.

α: Pd related peak (most appropriate T). (Pd/CeO2 HTA)

β: Appears when PGMs are present (desorption T too high).

NOx desorption curves (NOx adsorption for 100 s)

100 200 300 400 500

0

4

8

12

16

20

24

NO

x c

on

ce

ntr

ati

on

(p

pm

)

Temperature (C)

Pt/CeO2 HTA

Pt-Pd/CeO2 HTA

Pd/CeO2 HTA

CeO2 HTA βα

Pd/CeO2 showed the highest PNA ability (50 % NSE).

13

100 200 300 400 500

0

20

40

60

80

100

NO

x c

on

ce

ntr

ati

on

(p

pm

)

Temperature (oC)

NOx adsorption for

50 sec

100 sec

200 sec

500 sec

1 h

3 h

α β

α*

Pd/CeO2 HTA, NOx desorption curves

Increase in adsorption time → New NOx desorption peak appears at α*

α and β: Saturates quickly, but the storage capacity is limited.

α*: Saturates slowly, but the storage capacity is large.

Effect of PGM and support

14

500 1000 1500 2000 2500 3000 3500 4000

0

20

40

60

80

100

Pd/CeO2 HTA

NO

x s

tora

ge

eff

icie

nc

y (

%)

NOx adsorption time (s)

100 1000 10000

0

20

40

60

80

100

Th

e a

mo

un

t o

f N

Ox d

es

orb

ed

(m

ol/

gc

at.)

NO adsorption time (s)

Pd/CeO2 HTA

Effect of adsorption time

As the NOx adsorption time increases, the amount of NOx stored in the catalyst increases, but the NOx storage efficiency also decreases sharply.

The amount of NOx stored & NOx storage efficiency

15

Pd/CeO2: Sulfur poisoning and regeneration

150 200 250 300 350 400 450 500

0

4

8

12

16

20

24

NO

x c

on

ce

ntr

ati

on

(p

pm

)

Temperature (oC)

HTA

Sulfur aging

Regeneration

Pd/CeO2


Sulfur aging250 ppm SO2, 5% H2O, 9.5% O2 and N2 with total flow rate of 200 ml/min at 300 °C for 24 h

Regeneration6% O2, 5% CO2, 10% H2O and N2 with total flow rate of 200 ml/min at 750 °C for 30 min

Pd/CeO2 HTA catalyst is extremely vulnerable to sulfur poisoning.

Regeneration of poisoned catalyst is also not reversible.

16

D.H. Kim et al. Catalysis Today, 2018, 307(1), 93-101.

D.H. Kim et al. Catalysis Today, 2017, 297(15), 53-59.

“Pd/CeO2” could be the candidate catalyst to reduce the NOx emission during the cold-start period. However, the catalytic activity is completely lost after the sulfur aging treatment.

Summary of Part 1

17





Contents

18

Chen, Hai-Ying, et al. Low Temperature NO Storage of Zeolite Supported Pd for Low Temperature Diesel Engine Emission Control. Catalysis Letters, 2016, 146(9) 1706-1711.

Pd/zeolite catalysts

1. Highly dispersed Pd at the exchange sites adsorb NO.

2. Zeolite framework structures affect the NOx storage capacity and the desorption temperature.

3. Good sulfur tolerance.

Pd/Zeolite as the Passive NOx Adsorbers ?

High NOx storage ability & High Sulfur tolerance

19

Pd/Zeolite as the Passive NOx Adsorbers ?

Feng Gao and János Szanyi et al. Low-Temperature Pd/Zeolite Passive NOx Adsorbers: Structure, Performance, and Adsorption Chemistry. The Journal of Physical Chemistry C, 2017, 121(29), 15793-15803

“NOx trapping and release are not simple chemisorption and desorption events but involve rather complex chemical reactions.”

“NO transport within different zeolite frameworks plays an important role in determining release temperatures.”

20

Pd/SSZ-13

SSZ-13 (Chabazite, support)

Hydrothermal stability

Sulfur resistance

Palladium (active metal)

Thermal stability

Oxidation ability

NO adsorption

Pd metal and ion (Pd0–2+) : Possiblea

Pd oxide (PdO): Impossibleb,c a: Catal Rev, 42 (2000) 71-144.b: J. Catal., 210 (2002) 295-312c: Appl. Catal., B, 23 (1999) 247-257

3.8 Å

21

Experimental

Pd/SSZ-13 preparation

Wet impregnation: WET

Incipient wetness impregnation: IWI

Ion exchange: ION

Solid-state ion exchange S-S

Pretreatment

Calcination (fresh): 500 ℃, 2 h, 15% O2 in N2

Hydrothermal aging (HTA): 750 ℃, 25 h, 15% O2, 10% H2O in N2

Characterization

XRD, STEM, XAFS, H2 TPR, XPS, DRIFT

22

NO adsorption ability: Influence of synthetic method

Regardless of synthesis methods, the NO adsorption ability of catalysts was activated after the HTA treatment.


150 200 250 300 350 400 450 500

0

2

4

6

8

10

12

14

IWI Fresh

WET Fresh

ION Fresh

S-S Fresh

NO

x c

on

ce

ntr

ati

on

(p

pm

)

Temperature (oC)

Pd(2)/SSZ-13

0

2

4

6

8

10

12

14

IWI HTA

WET HTA

ION HTA

S-S HTA

Temperature (oC)

NO

x c

on

ce

ntr

ati

on

(p

pm

)150 200 250 300 350 400 450 500

Pd(2)/SSZ-13

23

0 1 2 3 4 5

5

10

15

20

25

30

Sum

High T. (> 300C)

Th

e a

mo

un

t o

f N

Ox d

eso

rbed

(m

ol/g

ca

t.)

Pd loading, measured by ICP (wt%)

Low T. (< 300C)

NO adsorption ability: Effect of Pd amount (IWI method)

150 200 250 300 350 400 450 500

0

2

4

6

8

10

12

14

NO

x c

on

cen

trati

on

(p

pm

)

Temperature (oC)

Pd(0.2)

Pd(0.5)

Pd(1)

Pd(2)

Pd(3)

Pd(5)

Pd/SSZ-13 HTA

NO adsorption ability of Pd/SSZ-13 gradually increased up to 2 wt% of Pd.

Above the optimum Pd loading (2 wt%), the PNA ability decreased.


24

30 32 34 36

2(o)

a.u

.

H-SSZ-13

Pd(0.2)

Pd(0.5)

Pd(1)

Pd(2)

Pd(3)

Pd(5)

Fresh

5 10 15 20 25 30 35 40

HTA

a.u

.

Fresh

Pd(2)/SSZ-13

2(o)

30 32 34 36

HTA

H-SSZ-13

Pd(0.2)

Pd(0.5)

Pd(1)

Pd(2)

Pd(3)

Pd(5)

2(o)

Pd(1) (PdO peak decreased)

Pd(3) (PdO peak similar)

Pd(5) (PdO peak increased)

HTA effect

XRD patterns

25

@ low Pd loading (< 3 wt%): The HTA treatment decreased the size of PdO.

@ high Pd loading (> 3 wt%): In addition to the formation of small PdO clusters, the HTA treatment seems to induce the significant PdO sintering.

HTA effect

0 2 4 6 8

Pd(2)

FT

mag

nit

ud

e (

a.u

.)

R (Å )

HTA

Fresh

Pd(3)

Pd(5)

0 2 4 6 8

Pd(1)

FT

mag

nit

ud

e (

a.u

.)

R (Å )

PdO (ref.)

Pd foil (ref.)

HTA

Fresh

Pd(0.5)

Pd-OPd-Pd

Pd-(O)-Pd

EXAFS spectra in R-space

26

HTA effect: Pd(1)/SSZ-13

250 nm

250 nm

Agglomerated Pdspecies in patches

HTA

Well dispersed Pd species within the whole particle

HAADF-STEM & EDX analysisCalcined

What is the nature of Pd species?

27

After HTA, the reduction peak intensity from bulk PdO decreased significantly.

In addition, the H2 consumption peaks from PdO appeared with the broader and smaller peaks at higher temperatures, indicating the production of Pdions after the HTA treatment.

-50 0 50 100 150 200 250 300

TC

D s

ign

al (a

.u.)

Temperature (oC)

Fresh

HTA

Pd(3)

Pd(2)

-50 0 50 100 150 200 250 300

TC

D s

ign

al (a

.u.)

Temperature (oC)

Fresh

Pd(1)

Pd(0.5)

-50 0 50 100 150 200 250 300

TC

D s

ign

al (a

.u.)

Temperature (oC)

Fresh

HTA

Pd(1)

Pd(0.5)

HTA effect

After HTA, the reduction peak from PdO decreases significantly in intensity.

In addition, the broad H2 consumption peak from ca. 25 to 125 °C appeared.

1000 4000Desorption of Ar

Reduction of PdO

Decomposition of PdHx

Sachtler et al. reported that the broad reduction peak from Pd ions in zeolite appears at the higher temperature than that from bulk PdOa, b, c, d, e.

a: J. Mater. Sci. Lett., 11 (1992) 623-626b: Appl. Catal. A-Gen., 167 (1998) 113-121c: Appl. Catal. B-Environ., 14 (1997) 1-11d: Appl. Catal., 75 (1991) 93-103e: Appl. Catal., 54 (1989) 189-202

H2-TPR spectra

28

NO adsorption: Pd(2)/SSZ-13

NO adsorbs on ionic Pd: 1810 and 1860 cm-1 (Pd2+-NO).

2000 1900 1800 1700

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Ab

so

rban

ce (

a.u

.)

Wavenumber (cm-1)

1 min

3 min

5 min

10 min

30 min

60 min

18

10

18

60

Pd-NO

Pd-NO

NO-DRIFT spectra (NO adsorption)

Chen, Hai-Ying, et al. Catalysis Letters, 2016, 146(9) 1706-1711.D.H. Kim et al. Applied Catalysis B, 2017, 212(5) 140-149Bell, A.T. et al. Journal of Catalysis, 1997, 172(2) 453-463D. Klissurski et al. Physical Chemistry Chemical Physics, 2004, 6, 3702-3709

29

150 200 250 300 350 400 450 500

0

4

8

12

16

20

Pd/SSZ-13 HTA

Pd/CeO2 HTA

NO

x c

on

cen

trati

on

(p

pm

)

Temperature (oC)

Pd/CeO2 vs. Pd/Zeolite: NOx adsorption activity

Catalyst 0.035 g(26.2 μmol/gcat.)

Catalyst 0.1 g(11.4 μmol/gcat.)


The PNA ability of Pd/SSZ-13 was higher than that of Pd/CeO2. (SV: 120,000 h-1)

30

150 200 250 300 350 400 450 500

0

2

4

6

8

10

12

14

NO

x c

on

cen

trati

on

(p

pm

)

Temperature (oC)

Pd/SSZ-13 HTA

Sulfur aging

Regeneration

150 200 250 300 350 400 450 500

0

4

8

12

16

20

24

NO

x c

on

cen

trati

on

(p

pm

)

Temperature (oC)

HTA

Sulfur aging

Regeneration

Pd/CeO2

Pd/CeO2 vs. Pd/Zeolite: Sulfur tolerance


Compared to Pd/CeO2, Pd/SSZ-13 exhibited the excellent sulfur resistance.

31

Summary of Part 2

Compared to Pd/CeO2, Pd/SSZ-13 exhibited the improved PNA ability as well as the excellent sulfur resistance.

The HTA treatment induced the formation of Pd ion species in SSZ-13, thus activating the PNA ability of Pd/SSZ-13.

Hydrothermaltreatment

D.H. Kim et al. Applied Catalysis B, 2017, 212(5) 140-149

32

2200 2000 1800 1600 1400 1200 1000

0.0

0.1

0.2

0.3

0.4

0.5

Ab

so

rban

ce (

a.u

.)

Wavenumber (cm-1)

Pd/SSZ-13

Pd/CeO2

0.1

Part 1 vs Part 2: Pd/CeO2 vs Pd/SSZ-13

NO2, NO3 speciesIonic Pd-NO

Pd/SSZ-13 and Pd/CeO2 have different NOx adsorption sites.

NO-DRIFT spectra (NO adsorption for 1 h)

33

100 200 300 400 500

0

20

40

60

80

100

NO

x c

on

cen

trati

on

(p

pm

)

Temperature (oC)

NOx adsorption for

50 sec

100 sec

200 sec

500 sec

1 h

3 h


150 200 250 300 350 400 450 500

0

2

4

6

8

10

12

14

16

18

20

50.0 mol/g cat

NO

x c

on

ce

ntr

ati

on

(p

pm

)Temperature (

oC)

NOx adsorption for

100 s

1 h

Pd(2)/SSZ-13 HTA

26.2 mol/g cat

Pd/CeO2 HTA

34

Sample Role of Pd Role of support

NO adsorbed

(μmol/gcatal.)

100 s 1 h

Pd/CeO2

Activation of

NO adsorption site (α)

(PdO-Ce interaction)NOx adsorption site

(CeO2)11.4 67.7Promotion effect of

NOx oxidation

(β, NO2→NO3)

(PdO-Ce interaction)

Pd/SSZ-13NO adsorption site

(Pd ion)

Stabilization of Pd ion

(SSZ-13)26.2 50.0


35





Contents

36

The optimum HTA temp. for the PNA ability was found at 700 ~ 750 oC.

Effect of HTA temperature on the PNA ability

150 200 250 300 350 400 450 500

0

2

4

6

8

10

12

14

NO

x c

on

cen

trati

on

(p

pm

)

Temperature (oC)

860 oC

800 oC

750 oC (Reference)

700 oC

650 oC

600 oC

500 oC

600 650 700 750 800 850

0

5

10

15

20

25

30

35

Th

e a

mo

un

t o

f N

Ox a

dso

rbed

(m

ol/g

ca

t.)

HTA temperature (oC)

Sum

NOx desorption at high T (> 300

C)

NOx desorption at low T (< 300

C)Optimum!

△ HTA temperatureNOx desorption curves (NOx adsorption for 100 s)

37

150 100 50 0 -50

Chemical shift (ppm)

HTA 850

HTA 750

Fresh

After HTA at high temp., de-alumination occurred in Pd/SSZ-13.

When the Al site of SSZ-13 decreases, the amount of Pd ions decreases and the PNA ability decreases.

150 100 50 0 -50

Chemical shift (ppm)

Effect of HTA temperature

27Al MAS-NMR spectra

38

The presence of H2O during HTA is essential for activating the NO adsorption ability of Pd/SSZ-13.

Effect of H2O conc. during HTA in the PNA ability

△ H2O conc. during HTA

150 200 250 300 350 400 450 500

0

2

4

6

8

10

12

14

NO

x c

on

cen

trati

on

(p

pm

)

Temperature (oC)

20 %

10 % (Reference)

5 %

0 %

0 5 10 15 20

0

5

10

15

20

25

30

35

40

Sum


C)


C)

Th

e a

mo

un

t o

f N

Ox a

dso

rbed

(m

ol/g

ca

t.)

H2O conc. (%)


39

150 200 250 300 350 400 450 500

0

2

4

6

8

10

12

14

NO

x c

on

cen

trati

on

(p

pm

)

Temperature (oC)

30 h

25 h (Reference)

15 h

5 h

2 h

0 h (Fresh)

0 5 10 15 20 25 30

0

5

10

15

20

25

30

35

Sum


C)


C)

Th

e a

mo

un

t o

f N

Ox a

dso

rbed

(m

ol/g

ca

t.)

HTA duration time (h)

△ HTA duration time

In order to activate the NO adsorptive ability of Pd/SSZ-13, more than 5 hours of HTA is required.

Effect of HTA duration time at 750 oC in the PNA ability


40

Na+ and K+ seem to inhibit the cation exchange of ionic Pd during the HTA treatment by occupying the Al sites in SSZ-13.

Effect of cations (Na+ and K+) in SSZ-13 on activation

150 200 250 300 350 400 450 500

0

2

4

6

8

10

12

14

NO

x c

on

ce

ntr

ati

on

(p

pm

)

Temperature (oC)

Pd/NH4-SSZ-13 HTA

Pd/Na-SSZ-13 HTA

Pd/K-SSZ-13 HTA


41

Summary of Part 3

D.H. Kim et al. Effect of various activation conditions on the low temperature NO adsorption performance of Pd/SSZ-13 passive NOx adsorber. Catalysis Today, in press.

42





Contents

43

Image from http://dannysengineportal.com/excessive-exhaust-smoke/

Catalysts are frequently exposed to reducing environments depending on engine operating conditions.

Therefore, it is necessary to understand the effect of the reducing gas on the behavior of the catalyst.

Effect of CO and H2 aging on the PNA ability

44

János Szanyi et al. Molecular Level Understanding of How Oxygen and Carbon Monoxide Improve NOx Storage in Palladium/SSZ-13 Passive NOx Adsorbers: The Role of NO

+ and Pd(II)(CO)(NO) Species. The Journal of Physical Chemistry C, 2018, 122(20), 10820-10827

“Adsorption of NO leads to the formation of Pd(II)–NO and Pd(I)–NO complexes as well as NO+ species that replace residual H+ (extra-framework) sites.”

“Because of shielding of the Pd(II) ion from excess water and selective formation of such stable coordinatively saturated Pd(II)(NO)(CO) complexes, the PNA performance is improved by CO.”

The effect of presence of CO on the PNA ability ?

45

Pd/SSZ-13 for diesel system

Material & Method

PGM: Pd (1 wt%)

Support: SSZ-13

Incipient wetness impregnation

Pretreatment

Calcination:

500 ℃, 2hr, 15% O2 in N2

Hydrothermal Aging (HTA):

750 ℃, 25hr, 15% O2, 10% H2O in N2

15% H2 or 1% CO at 500 – 900 ℃

9.5% O2, 5% H2O, 5% CO2

9.5% O2, 5% H2O, 5% CO2 , 100ppm NO

120 ℃

500 ℃

Time

NO adsorption

(100s)

NOon

(10℃/min)

30minP

reco

nd

itio

nin

g

NO

xd

eso

rpti

on

30min

(10℃/min)

2 hr

(10℃/min)

900 ℃

Re

du

ctio

n

Activity measurement: after H2 or CO aging

46

After the reductive aging under H2, the PNA ability steadily decreased.

After the reductive aging under CO, the PNA ability steeply decreased.

150 200 250 300 350 400 450 500

0

2

4

6

8

10

12

HTA

NO

x c

on

ce

ntr

ati

on

(p

pm

)

Temperature (oC)

H2 aging at 500

oC

H2 aging at 600

oC

H2 aging at 700

oC

H2 aging at 800

oC

H2 aging at 900

oC

150 200 250 300 350 400 450 500

0

2

4

6

8

10

12

HTA

NO

x c

on

cen

trati

on

(p

pm

)

Temperature (oC)

CO aging at 500 oC

CO aging at 600 oC

CO aging at 700 oC

CO aging at 800 oC

CO aging at 900 oC


Pd(2)/SSZ-13 Pd(2)/SSZ-13


47

500 600 700 800 900

0

20

40

60

80

100

Rem

ain

ing

PN

A a

bilti

y (

%)

Aging temperature (oC)

Aging under H2

Aging under CO


Remaining PNA ability (%)=𝑇ℎ𝑒 𝑃𝑁𝐴 𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑎𝑓𝑡𝑒𝑟 𝑟𝑒𝑑𝑢𝑐𝑡𝑖𝑣𝑒 𝑎𝑔𝑖𝑛𝑔

𝑇ℎ𝑒 𝑃𝑁𝐴 𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑎𝑓𝑡𝑒𝑟 𝐻𝑇𝐴× 100

48

0 2 4 6

Pd-Pd

Pd-O

FT

ma

gn

itu

de

(a

.u.)

R (Å )

Pd-(O)-Pd (bulk PdO)

H2 aging at 500

oC

H2 aging at 600

oC

H2 aging at 700

oC

H2 aging at 800

oC

H2 aging at 900

oC

HTA

Pd(2)/SSZ-13

0 2 4 6

FT

ma

gn

itu

de

(a

.u.)

R (Å )

CO aging at 500 oC

CO aging at 600 oC

CO aging at 700 oC

CO aging at 800 oC

CO aging at 900 oC

HTA

Pd(2)/SSZ-13

Pd-O

Pd-Pd

Pd-(O)-Pd (bulk PdO)

EXAFS spectra in R space

Effect of CO and H2 aging on the state of Pd

The particle size of the metal Pd grows bigger and faster after the CO agingthan after the H2 aging.

49

H2 700 CO 700

50

nm

50

nm

Effect of CO and H2 reduction at 700 C on Pd sintering

More Pd sintering is observed in CO treated sample, probably due to the formation of volatile Pd-carbonyl.

50

H2 treatment

Limited Pd sintering occurred.

Gradual decrease in PNA performance

CO treatment

Considerable Pd sintering occurred due to the volatile Pd-CO.

Abrupt decrease in PNA performance

Summary of Part 4

Y.S. Ryou, D.H. Kim et al. under revision.

51

Thank you!

Prof. Do Heui Kim

Jaeha Lee

Yongwoo Kim Sungha Hwang

PNA team

Dr. YoungSeok Ryou(LG Chem)

52

Acknowledgement

, Yongwoo Kim , Sungha Hwang , Chang Hwan Kim *[email protected] · 2018-10-08 · 1School of Chemical...

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Transcript of , Yongwoo Kim , Sungha Hwang , Chang Hwan Kim *[email protected] · 2018-10-08 · 1School of Chemical...