View
1
Download
0
Category
Preview:
Citation preview
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*
*dohkim@snu.ac.kr
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
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
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
NOx desorption curves (NOx adsorption for 100 s)
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
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
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.
NOx desorption curves (NOx adsorption for 100 s)
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.
NOx desorption curves (NOx adsorption for 100 s)
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.)
NOx desorption curves (NOx adsorption for 100 s)
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
NOx desorption curves (NOx adsorption for 100 s)
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
Part 1 vs Part 2: Pd/CeO2 vs Pd/SSZ-13
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
Part 1 vs Part 2: Pd/CeO2 vs Pd/SSZ-13
35
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
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
NOx desorption at high T (> 300
C)
NOx desorption at low T (< 300
C)
Th
e a
mo
un
t o
f N
Ox a
dso
rbed
(m
ol/g
ca
t.)
H2O conc. (%)
NOx desorption curves (NOx adsorption for 100 s)
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
NOx desorption at high T (> 300
C)
NOx desorption at low T (< 300
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
NOx desorption curves (NOx adsorption for 100 s)
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
NOx desorption curves (NOx adsorption for 100 s)
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
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
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
Effect of CO and H2 aging on the PNA ability
Pd(2)/SSZ-13 Pd(2)/SSZ-13
NOx desorption curves (NOx adsorption for 100 s)
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
Effect of CO and H2 aging on the PNA ability
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
Recommended