pd/zeolite passive hc/nox adsorbers€¦ · , mark crocker. 2,3, jeroen van der mynsbrugge. 4,...
TRANSCRIPT
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CLEERS WorkshopSeptember 19, 2018
Pd/Zeolite Passive HC/NOx Adsorbers
Trevor Lardinois1, Jason Bates1, Rajamani Gounder1, Robert B. Pace2,3, Yaying Ji2, Mark Crocker2,3, Jeroen Van der Mynsbrugge4, Alexis Bell4
1Charles D. Davidson School of Chemical Engineering, Purdue University2University of Kentucky Center for Applied Energy Research
3Department of Chemistry, University of Kentucky4Department of Chemical and Biomolecular Engineering, University of California, Berkeley
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Objectives:• Obtain fundamental understanding of the chemistry of NOx adsorption and reduction in
Pd/zeolites• Tailor Pd/zeolites with respect to performance and durability for application as HC/NOx
adsorbers
Partners:University of California, Berkeley University of Kentucky Purdue UniversityOak Ridge National LaboratoryFord Motor Co.BASF
Pd2+
PdOH+
Pd/H-BEANO
Ethylene
Toluene
While this technology should be applicable to both gasoline and diesel vehicles, gasoline applications are emphasized in this project, given the importance of stoichiometric engines in the U.S. automotive market
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Role of Zeolite Framework
• LT NO storage capacity: BEA > ZSM-5 > CHA• Strength of NO-Pd bond: CHA > ZSM-5 > BEA• HC adsorption capacity: BEA > ZSM-5 > CHA
BEA appears to be the most promising system for this application but is complex (9 discrete Al sites)
CHA represents a simple system, very amenable to study (only 1 framework Al site)
Y. Murata, T. Morita, K. Wada, H. Ohno, SAE Technical Paper 2015-01-1002.H. Chen, J.E. Collier, D. Liu, L. Mantarosie, D. Durán-Martin, V. Novák, R.R. Rajaram, D. Thompsett, Catal. Lett., 2016, 146, 1706-711.A. Vu, J. Luo, J. Li, W.S. Epling, Catal. Lett., 2017, 147, 745-750. Y. Zheng, L. Kovarik, M.H. Engelhard, Y. Wang, Y. Wang, F. Gao, J. Szanyi, J. Phys. Chem C, 2017, 121, 15793-15803Y. Ryou, J. Lee, S.J. Cho, H. Lee, C.H. Kim, D.H. Kim, Appl. Catal. B, 2017, 212, 140-149.J. Lee, Y. Ryou, S.J. cho, H. Lee, C.H. Kim, D.H. Kim, Appl. Catal. B, 2018, 226, 71-82. K. Khivantsev, F. Gao, L. Kovarik, Y. Wang, J. Szanyi, J. Phys. Chem. C, 2018, 122, 10820-10827. O. Mihai, L. Trandafilovic, T. Wentworth, F.F. Torres, L. Olsson, Top. Catal., 2018, https://doi.org/10.1007/s11244-018-1017-z A. Porta, T. Pellegrinelli, L. Castoldi, R. Matarese, S. Morandi, S. Dzwigaj, L. Lietti, Top. Catal., 2018, https://doi.org/10.1007/s11244-018-1045-8
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Sample Preparation: NH4+ Back Exchange Parity Plot
4
Procedure for NH4+ back exchange
1. 50 gsoln / gzeo of 1 M NH4NO3
2. 20 hours at 65 oC3. Quantify Pd in supernatant
NH4+ selectively and quantitatively removes isolated Pd ions (measured by H2
TPR) in CHA and BEA zeolites Proportion of isolated Pd ions in BEA is insensitive to the Pd loading in range
studied
Pd-BEA-3 (0.1%)
Pd-CHA-1(1%)
Pd-BEA-1 (1%)
Pd-BEA-4(0.5%)
Sample preparation:1. Incipient wetness impregnation 2. Commercial BEA (Si/Al = 11)3. CHA synthesized in house (Si/Al = 14)
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Ex Situ Microscopy on Pd-CHA
Data and analysis courtesy of Dr. K. Unocic at ORNL
DF-STEM
Small ~2 nm particles
Larger Pdparticles (<20nm)
Small ~2 nm particles
BF-STEM EDS
Summary
• Two sizes of Pd particles – small ~2 nm and large (< 20 nm)
• Small particles are uniformly distributed
• Findings consistent with relatively low content of ionic (isolated) palladium in as–prepared sample
5
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H2 TPR on Pd-Beta and Reversibility
0.0
0.5
1.0
1.5
2.0
2.5
200 300 400 500 600H 2
Cons
umpt
ion
/ μm
ol g
-1s-1
Temperature / K
H-Beta
Pd-Beta-3 (0.1wt%)823 K oxidized
Pd-Beta-4 (0.5wt%)823 K oxidized
Pd-Beta-4 (0.5wt%)823 K re-oxidizedafter 1123 K reduction
x2
x10
x2
0.1% Pd-Beta (823 K oxidized)• H2/Pd (285–350 K) = 0.32 PdO• H2/Pd (350–550 K) = 0.67 Pd2+
0.5% Pd-Beta (823 K oxidized)• H2/Pd (280–360 K) = 0.25 PdO• H2/Pd (360–600 K) = 0.78 Pd2+
0.5% Pd-Beta (823 K oxidized after 1123 K reduction)• H2/Pd (262–360 K) = 1.0 PdO• H2/Pd (360–550 K) = 0.10 Pd2+
Pd cannot be re-dispersed after high T reduction
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Pd/BEA Baseline: NOx Uptake Experiments
7
Experimental Details• 121.6 mg of Pd/BEA, 180-250 micron pellets,
pretreated at 500 oC in 10% O2.• 1007.5 sccm, 10 kPa O2, balance N2, bypass 10
minutes, switch to reactor at 100 oC for 10 minutes,40 minute temp ramp to 500 oC
NOx Uptake in first 10 minutesNOx / Pd = 1.15 & 0.92 (duplicate runs)NOx / Pd = 1.26*
*Zheng, et al., J. Phys. C., 2017, 121, 15793 - 15803
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0.00
0.50
1.00
1.50
2.00
2.50
18001900200021002200230024002500
Unreduced Catalyst
0.000.100.200.300.400.500.600.700.800.901.00
1900200021002200230024002500
Catalyst reduced at 500 °C0 Minutes
10 minutes
20 minutes
30 minutes
40 minutes
50 minutes
60 minutes
Pd Speciation in Pd/BEA: Effect of Reduction Temperature (CO adsorption at 25 oC after Ar purge at 500 oC; H2 reduction at 100 oC, 300 oC, 500 oC)
2098
2098
2080
211821
402154
2193
2214
2193
1958
1958
• Very little ionic Pd remains after reduction at 500 oC
• Decreased CO adsorption after catalyst reduction at high temperature
Wavenumber (cm-1)
Wavenumber (cm-1)
Abso
rban
ce (a
.u.)
Abso
rban
ce (a
.u.)
8
0
40
80
120
160
0 20 40 60CO adsorption time (min)
Pd-C
O b
ands
pea
k ar
ea (a
.u.) Ar purge
Reduced@100 oC
Reduced@500 oC
Reduced@300 oC
Linear Pd-CO bands between 2230 and 2028 cm-1
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NO Adsorption on Pd/BEANO adsorption at 25 oC after Ar purge at 500 oC for 1 h
Abso
rban
ce (a
.u.)
1500 2000 2500 3000 3500 Wavenumber (cm-1)
0.2
60 min
1 min
20 min
10 min
30 min
5 min
26441883,1844
16542466
3670/3645
3778
3740 3600
2166
9
IR band assignments:2400 – 2650 cm-1: Fermi resonance of
OH stretch*2166 cm-1: NO+
1883, 1844 cm-1: Cationic Pd-NO1654 cm-1: NO2 ads. on OH group
100 ppm NO, bal. N2
* M.F. Claydon, N. Sheppard, J. Chem. Soc., Chem. Comm., 1969, 1431-1433.
A.G. Pelmenschikov, J.H.M.C. van Wolput, J. Jaenchen, R.A. van Santen, J. Phys. Chem., 1995, 99, 3612-3617.
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Effect of Reduction Temperature on NO AdsorptionNO adsorption at 25 oC after H2 reduction at 300 oC and 500 oC
Wavenumber (cm-1)
Wavenumber (cm-1)
Abso
rban
ce (a
.u.)
Abso
rban
ce (a
.u.)
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
15001600170018001900200021002200
Catalyst Reduced at 300 °C
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
15001600170018001900200021002200
Catalyst Reduced at 500 °C
10 Minutes
20 Minutes
30 Minutes
40 Minutes
50 Minutes
60 Minutes
Limited NO adsorption after catalyst reduction at 300 oCbut no adsorption after reduction at 500 oC
NO adsorption sites correspond to Pd ions
10
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Can Reduced Pd be Re-Oxidized/Re-Dispersed? CO Adsorption on Pd-BEA: Repeated Reduction/Oxidation Cycles
• Sample was reduced at 500 °C under hydrogen for 1 h, oxidized at 500 °C under air for 1 h; CO adsorption was conducted at 25 °C for 1 h in both cases
• Main bands observed at 2098 cm-1 and 1950 cm-1 (Pd0) on reduced catalyst • Intensities of main bands relatively unchanged from one cycle to the next, although
2211 and 2190 cm-1 bands (Pd3+/Pd4+) largely disappear11
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1900200021002200230024002500
Abso
rban
ce (a
.u.)
Wavenumbers (cm-1)
CO Adsorption after Reduction
1st Cycle
2nd Cycle
3rd Cycle
4th Cycle
5th Cycle
2098
2189
0
0.2
0.4
0.6
0.8
1
1.2
1900210023002500
Abso
rban
ce (a
.u.)
Wavenumbers (cm-1)
CO Adsorption after Oxidation
1st Cycle
2nd Cycle
3rd Cycle
4th Cycle
5th Cycle
2146
2115
2098
2212
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1900 2000 2100 2200 2300 2400 2500
Abso
rban
ce (a
.u.)
Wavenumbers (cm-1)
0.5
2 min
5 min10 min
20 min30 min45 min60 min
2214
2193
2154
2140 21
1820
9820
80
1958
Pd-CHA: Pd speciationComparison of Pd-CO bands for Pd-CHA and Pd-BEA
(pre-treatment in Ar at 500 oC for 1 h)
Pd-CHA-1 Pd-BEA
Compared to Pd-BEA, Pd-CHA shows fewer CO bands. CO distribution over the two samples is also different. Relative to other bands,
the bands at 2211 and 2190 cm-1 (Pd3+/Pd4+) are more significant for Pd-CHA than Pd-BEA.
Wavenumber (cm-1)
1 min2 min
5 min
10 min
20 min
30 min
1600 1700 1800 1900 2000 2100 2200 2300
1.0
Abso
rban
ce (a
.u.)
2211 21
9021
6421
4221
2621
13
1900
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13
Pd-CHA: Comparison of Pd-CO Bands after H2 Reduction (CO adsorption at 25 oC for 2 min)
1900 2000 2100 2200 2300 2400 2500
Ar@500 C
H2@100 C
H2@300 C
Abso
rban
ce (a
.u.)
Wavenumber (cm-1)
0.5
2210
2189
2142
2163
2125
2365
2350
Comparison of the Pd-CO bands clearly shows that CO adsorption declines after reduction, with a very significant drop after reduction at 300 oC.
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Pd-CHA: Reduced at 100 °C
2.0
1000 1500 2000 2500 3000 3500
Abso
rban
ce (a
.u.)
Wavenumber (cm-1)
30 min 30 min
NO + CO co-adsorption @100 ° CNO adsorption @100 °C
In the NO-only case, evolution of OH bands and background are significant;Pd-NO band is almost unobservable
With CO present, Pd-CO and Pd-NO bands are observed simultaneously; Pd-CO region consistent with formation of Pd(CO)(NO)2+ complex
CO promotes NO adsorption
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1600 1800 2000 2200 2400
0.5
Abso
rban
ce (a
.u.)
Wavenumber (cm-1)
2 min
5 min
10 min
20 min
1 min
1600 1800 2000 2200 2400
0.5
Abso
rban
ce (a
.u.)
Wavenumber (cm-1)
2 min
5 min
10 min
20 min
1 min
Abso
rban
ce (a
.u.)
1600 1800 2000 2200 2400
1.0
Wavenumber (cm-1)
2 min
5 min
10 min
20 min
1 min
Pd-CHA: Can Reduced Pd be Re-Oxidized/Re-Dispersed?
Ar purged at 500 °C H2 reduced at 300 °C Re-oxidized at 500 °C
Compared to Ar purge, Pd-CO bands become weaker after reduction After being re-oxidized at 500 °C, the original Pd species are re-formed to some
extent
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1600 1800 2000 2200 2400
0.5Ab
sorb
ance
(a.u
.)
Wavenumber (cm-1)
2 min
5 min
10 min
20 min
30 min
1 min
Pd-CHA: Effect of calcination at 750 °C(CO adsorption at 25 °C)
1600 1800 2000 2200 2400
0.5
2 min
5 min
10 min
20 min
30 min
1 min
15 min
Abso
rban
ce (a
.u.)
Wavenumber (cm-1)
Ar purged at 500 °C H2 reduced at 500 °C
• Compared to calcination at 550 °C (as prepared), little change is observed in the distribution of Pd-CO bands after sample re-calcination at 750 °C
• Notably, Pd-CO bands are still significant even after reduction at 500 °C for the sample calcined at 750 °C
Results consistent with calcination at high temperature improving Pd dispersion, such that after reduction Pd sintering is less severe
Y. Ryou, J. Lee, S.J. Cho, H. Lee, C.H. Kim, D.H. Kim, Appl. Catal. B, 2017, 212, 140-149.
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Computational Studies: CO and NO Adsorption
∆Gads [kJ/mol] T = 298.15 K, P = 1 atm; quasi-RRHO
LOT: T8 (g): ωB97X-D/Def2-SV(P); T8 (QM/MM): ωB97X-D/Def2-TZVPD // ωB97X-D/Def2-SV(P)
CO interacts more strongly with Pd sites than NO; CO and NO adsorb most strongly on Pd0 + H-Z
H-Z Pd0 + H-Z Pd+Z- PdOH+Z-
COT8 (g) +7 -157 -88T8 (QM/MM) +11 -152 -97NOT8 (g) +11 -89 -79 -54T8 (QM/MM) +13 -87 -63
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T696 Cluster Model for CHA Used in QM/MM Calculations
(Avoids boundary effects)
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isolated Al proximate Al pairHZ ZH—HZ
Pd0+HZ ↔ PdH+ Z- ZH—Pd0+HZPd+ Z- ZH—Pd+Z-
Z- Pd2+ Z-
PdO+HZ ↔ PdOH+ Z- ZH—PdO+HZ ↔ ZH—PdOH+ Z-
Possible Pd Exchange Sites at Isolated Al Atoms and Proximate Al Pairs in Zeolites
(Pd oxidation state = 0, 1, 2)
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Configurational Search To assess structural and energetic variations between chemically equivalent configurations
NNNN Al pair in 6R
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• Configurational search revealed significant variations (up to ~50 kJ/mol) in free energy between different configurations of Pdn+
sites. • Characteristics of Pd2+,
Pd+ and Pd0 are relatively independent of their specific environment (isolated Al, NNN or NNNN Al pairs).
Configurational Search: Summary
Lowest free energy configurations for Pdn+
(n=0,1,2) sites at isolated Al and proximate Al pairs in CHA.
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Interaction of PdO with CHA
22
For isolated Al and NNN Al pairs, the interaction of PdO with the Brønsted acid protons was also investigated. Regardless of the starting configuration, PdOwas found to protonate, forming PdOH+ Z-.
Lowest free energy configurations for PdO interacting with isolated Al (PdOH+Z-, left) and NNN Al pairs (PdOH+Z- H+Z-, center). Configuration of water molecule adsorbed at Pd2+Z- Z-
site (right).
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Summary (1)
• Pd/BEA and Pd/CHA:- NO adsorption sites correspond to Pd ions- reduction with H2 at ≥ 300 oC results in decreased CO and NO adsorption- re-oxidation at 500 oC (after reduction at 500 oC) unable to bring catalyst completely back to original state
• Pd/CHA:- presence of CO promotes NO adsorption via formation of Pd(CO)(NO)2+
complex- calcination at 750 oC appears beneficial w.r.t. preventing Pd sintering and retaining adsorption capacity after high temperature reduction
• For practical applications, protection against rich transients will be necessary
23
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Summary (2)
• CO interacts more strongly with Pd sites than NO; CO and NO adsorb most strongly on Pd0 + H-Z
• To assess structural and energetic variations between chemically equivalent configurations, a full configurational search was performed (> 100 different geometries)
• This configurational search revealed significant variations (up to ~50 kJ/mol) in free energy between different configurations of Pdn+ sites.
• Characteristics of Pd2+, Pd+ and Pd0 are relatively independent of their specific environment (isolated Al, NNN or NNNN Al pairs).
• For isolated Al and NNN Al pairs, PdO was found to protonate, forming PdOH+ Z-
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Acknowledgements
• Ford Motor Co.:Christine LambertAndrew (Bean) GetsoianJoe TheisJason LupescuJustin Ura
• U. California, Berkeley:Martin Head-Gordon
• ORNL: Vitaly PrikhodkoKinga UnocicJae-Soon Choi
• BASF:Saeed Alerasool
• DOE (Vehicle Technologies Office):Aaron YocumKen Howden