effects of hydrothermal aging on the performance of four
TRANSCRIPT
Effects of Hydrothermal Aging on the Performance of Four Different Formulations of
Three-way Catalyst in Exhaust Conditions Relevant to Propane Engines
Acknowledgements: This research is supported by DOE-VTO Fuels Technologies and catalysts provided by Umicore
Daekun Kim 1, Todd J. Toops2, Nguyen Ke1 , Pranaw Kunal21Universty of Tennessee, Knoxville, TN, USA, 2Oak Ridge National Laboratory, Oak Ridge, TN, USA, Email: [email protected] (Daekun Kim), [email protected] (Todd J. Toops)
Motivation and Objectives
Formulation of Three-way Catalysts (TWCs)
• Propane has numerous advantages as fuel in vehicles due to
1) Lower emissions of green house gases (~13% less) than gasoline vehicles
[Gregory Kerr, Neil Leslie, P. R. GHG and Criteria Pollutant Emissions Analysis. (2017)]
2) Reducing the risk of engine knocking and potential damage because of higher octane
rating than gasoline
• Previous study has shown the impact of different formulations of TWC on propane
reactivity
[2019 CLEERS, https://cleers.org/cleers-workshops/workshop-presentations/entry/2084/]
• In the present study, the effects of hydrothermal degradation of four different
formulations of a family of prototype TWC are investigated using simulated exhaust
gases with C3H8 as the only hydrocarbon component
• Performance of TWCs investigated via
• TWC sample of 2.2 cm in diameter and 2.54 cm in length with a total of ~292 cells• Sample is positioned at the exit of the furnace• All chemical species (NO, CO, CO2, C3H8, NH3, and N2O) are measured with a FTIR analyzer• All TWC samples were hydrothermally-aged in a bench flow reactor at 820°C for 50h,
followed by further aging at 900°C for 50h under prescribed US-DRIVE aging conditions (HTA-900)- Performing 1 min cycling between succeeding neutral (10% CO2, 10% H2O and N2 balance for 40 s), rich (10% CO2, 10% H2O, 3% CO, 1% H2 and N2 balance for 10 s) and lean (10% CO2, 10% H2O, 3% O2, and N2 balance for 10 s)
Oxygen storage capacity (OSC) Mode Time Gas CompositionLean 20 min 1.5% O2, balance N2
Rich 5 min 0.2% CO, balance N2
• OSC is performed from 550 to 150℃ in 200℃ decrements
• Oxygen can be stored on OSC material as well as platinum group metals (PGM)
• Interestingly, OSC of fresh ORNL4 (with MOSC) at 550℃ is highest compared to fresh ORNL5 (with HOSC)
• Based on ORNL4 and ORNL5 results, the function of OSC material is degraded after hydrothermal aging (phase segregation and agglomeration of the cerium oxide)
Surface Characterization StudiesBET surface area BJH pore volume
Water gas-shift (WGS) reaction
• Fresh with OSC samples (ORNL4 and ORNL5) exhibit higher reactivity of WGS reaction than that of fresh without OSC (ORNL2 and ORNL6)
• However, more degradation of WGS for ORNL4 and ORNL5 after hydrothermal aging
• Low reactivity of WGS reaction for ORNL4 HTA-900 possibly due to low Pd loading than other TWC samples
• Gas mixture consists of 0.5% CO, 13% H2O, and N2 balance at a GHSV of 60,000 h-1 ; temperature ramp: 200-600℃ at a heating rate of 5℃/min Conclusions
– Light-off temperatures (T50, T90) for NO, CO and C3H8
– Oxygen storage capacity (OSC)
– Steam reforming (SR) and water gas-shift (WGS) reactivity
– Characterization studies (Physisorption)
T50 and T90 light-off temperatures
• For fresh ORNL4 and ORNL5 the presence of OSC material improves conversion of NO and C3H8, whereas conversion of CO decreases
• T50 and T90 of NO, CO, and C3H8 for ORNL2 and ORNL4 are more affected by hydrothermal aging than ORNL5 and ORNL6 at 900°C
• Best performance (less degradation) is obtained for ORNL5 HTA-900 (T90 for NO and C3H8
are lowest)
• Simulated exhaust gases consist of 1000 ppm C3H8, 0.5% CO, 0.1% NO, 0.78% O2, 0.167% H2, 13% H2O, 13% CO2, and balance N2 at a GHSV of 60,000 h-1; temperature ramp: 100-600℃ at a heating rate of 5℃/min
Bench Flow Reactor Results
Sample
IDDescription Pd (g/l) Rh (g/l) OSC
ORNL2 (Pd6.36+Rh0.14 w/o OSC) 6.36 0.14 N
ORNL6 (Pd6.5 w/o OSC) 6.50 0 N
ORNL5 (Pd6.5 with HOSC) 6.50 0 High
ORNL4 (Pd4.06 with MOSC) 4.06 0 Medium
• Four different formulations of a family of prototype TWCs supplied by Umicore are investigated
• The formations differ in the loading of Pd/Rh and the amount of the oxygen storage material
• Cell density of all TWCs is 600 cpsi
Steam reforming (SR) reaction• Gas mixture consists of 0.1% C3H8, 13% H2O, and N2 balance at a GHSV of 60,000 h-1 ;
temperature ramp: 200-600℃ at a heating rate of 5℃/min
BJH pore size
• For fresh ORNL5 with high OSC (HOSC), OSC appears to inhibit SR reaction
• For fresh ORNL4 with medium OSC (MOSC), low SR reaction due to low Pd loading as well as OSC material
• SR reaction for fresh and HTA900 ORNL4 is worse than other TWC samples
• More CO produced for all HTA-900 TWC samples due to low reactivity of WGS than each fresh TWC sample
• Fresh TWC samples with OSC (ORNL4 and ORNL5) have larger BET surface area and pore volume compared to fresh TWC samples without OSC (ORNL2 and ORNL6), resulting in highest propane reactivity, WGS and OSC
• Significantly losses in catalyst surface area with OSC TWC samples (ORNL4 and ORNL5)
• Pore volume of ORNL5 and ORNL4 (with OSC) decreases after HTA, but not ORNL2 and ORNL6(without OSC)
• For fresh ORNL4 and ORNL5 presence of OSC material improves
conversion of NO and C3H8, whereas conversion of CO decreases
• OSC material appears to enhance WGS reaction, whereas inhibit SR
reaction
• Interestingly, OSC of fresh ORNL4 (with MOSC) at 550℃ is highest
compared to fresh ORNL5 (with HOSC) possibly due to high pore volume,
resulting in high accessibility of OSC material
• Even though the BET surface area and pore volume for ORNL4 HTA-900 are
higher than ORNL5 HTA-900, the performance of ORNL5 HTA-900 TWC is
better than of ORNL4 HTA-900 due to high pd loading
• After hydrothermal aging, ORNL5 (Pd6.5g/l with HOSC) offer the best
performance regarding to T50 and T90 for both NO and C3H8, WGS reaction
and OSC
C3H8 + 3H2O → 3CO + 7H2
Overall reaction: C3H8 + 6H2O → 3CO2 +10H2
CO + H2O ↔ CO2 + H2
For additional information, contact:
9/16/2020PNNL is operated by Battelle for the U.S. Department of Energy |
150
200
250
300
350 T90
T50
Pure component
Mixture component
T 50 o
r T 9
0 (°C
)
+ +
+++
Surrogate
BOB i-Octane
n-Heptane
Toluene
1-Hexene
30wt.%50 mol.%
50 mol.%50 mol.%
50 mol.%
150
200
250
300
350 T90
T50
Pure component
Mixture
T 50 o
r T 9
0 (°C
)
+
30wt.%
1%Pd/Pt1-CeO2
2%Pt/Pt1-CeO2
Cummins DOC
Low temperature catalytic oxidation of unburned high-performance fuels for control of advanced compression ignition (ACI) engine emissionsFan Lin, Kenneth G. Rappe, Yong Wang
Fan Lin
509-372-6922
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA, USA
Gas Conc.
O2 10%
CO2 6%
H2O 6%
CO 2000ppm
H2 400ppm
NO 800ppm
Fuel 3000ppm C1
OXIDATION OF PURE FUEL COMPONENTS
OXIDATION OF BLENDED FUELS
150
200
250
300
350 T90
T50
Pure component
Mixture component
T 50 o
r T 9
0 (°C
)
+ ++++
Surrogate
BOB i-Octane
n-Heptane
Toluene
1-Hexene
30wt.% 50 mol.% 50 mol.%50 mol.%
50 mol.%
OPTIMIZATION OF CATALYSTS CONCLUSIONS
ACKNOWLEDGEMENTS
Funding support from Co-optima Facility support from EMSL
Exhaust mixture
Commercial DOC 3%Pd/Pt1-CeO2
100
150
200
250
300
350T90
T50
1% Pd/Pt1-CeO2
Cummins DOC
T 50 o
r T 9
0 (°C
)
100
150
200
250
300
350T90
T50
1% Pd/Pt1-CeO2
Cummins DOC
T 50 o
r T 9
0 (°C
)
Oxidation of Pure Fuel Components CO oxidation
55%
25% 15%
5%
Surrogate BOB fuel
Pt is more active than Pd
for HC oxidation.
2%Pt/Pt1-CeO2 shows
higher activity than the
commercial DOC for both
BOB fuel and iso-butanol
blendstock.
Pt1CeO2
2% Pt
REFERENCES[1] Rappé. K.G., et al., Emission Contr. Science and Technology 5-2
(2019) 183-214.
200
MOTIVATION
► The DOE-funded Co-optimization of Fuels and Engines
(Co-Optima) aims to simultaneously develop high
performance fuels and high efficiency engines to reduce
petroleum consumption.
► The advanced compression ignition (ACI) engine
challenges the emission control with high HCs and low
exhaust temperature.
OBJECTIVE
► Quantitatively evaluate the light-off behavior of unburned
fuels on different oxidation catalysts to offer guidance for
optimizing fuel components and aftertreatment catalysts for
ACI engines.
APPROACH
► Both a commercial diesel oxidation catalyst (DOC, from
Cummins Emission Solutions) and two custom-synthesized
Pd/Pt/CeO2 catalysts were tested.
► The custom Pd/Pt/CeO2 catalysts were synthesized by
atomically dispersing 1wt.% Pt on CeO2 support followed
by additional loading of 1-3 wt.% Pd or 2 wt.% Pt.
► The light-off behaviors of both single fuel components and
fuel blends were evaluated with synthetic exhaust following
the U.S. DRIVE Low-Temperature Oxidation Catalyst Test
Protocol [1] employing conditions associated with low-
temperature combustion of gasoline (LTC-G) (protocol also
available at http://cleers.org).
► Oxygenates typically light off at
lower temperature than HCs.
► 1%Pd/Pt1-CeO2 is more active for
oxygenated components.
► Commercial DOC is more active for
HC components.
► CO light-off is hindered by
unsaturated fuel components.
► CO oxidation is less hindered by
saturated HC and oxygenates.
► On commercial DOC, the surrogate
BOB components and the iso-
butanol blend do not significantly
impact the oxidation reactivity of
each other.
► On the home-made 3%Pd/Pt1-
CeO2 catalysts, the unsaturated
HCs in the BOB fuel hinder the
oxidation of iso-butanol blend.
► In terms of the oxidation of pure fuel component, oxygenates are more
reactive than hydrocarbons (HCs). In comparison to the commercial DOC, the
1%Pd/Pt1-CeO2 catalyst is less active for HCs but more active for oxygenates.
► For blended fuel oxidation, on the commercial DOC, the surrogate BOB fuel
and the iso-butanol blend stock do not impact the light-off behavior of each
other. In contrast, on the 3%Pd/Pt1-CeO2 catalyst, the unsaturated HCs
(aromatic and alkene) in the surrogate BOB hinder the light-off of the more
reactive component iso-butanol.
► 2%Pt/Pt1-CeO2 shows superior activity for both the BOB fuel and the iso-
butanol blendstock, presenting a potential catalyst design to improve the
performance of low temperature oxidation of unburned fuels.
Non-catalytic gas-phase NO oxidation in the presence of decaneChih Han Liu1, Kevin Giewont1, Todd J. Toops2, Eric A. Walker3, Caitlin Horvatits1 and Eleni A. Kyriakidou1,*
1Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA2National Transportation Research Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA3Institute of Computational and Data Sciences, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA
*Email: [email protected] (Eleni A. Kyriakidou)
Conclusions
• NO was oxidized in a diesel exhaust gas phase
mixture.
• This reaction was due to the presence of n-
C10H22.
• C and N balance suggests the species formed
during the mutual oxidation of NO and n-C10H22.
• DFT suggests two feasible intermediate
radicals to oxidize NO to NO2 are ·C10H21O2
and ·HO2.
Introduction
• Gas phase oxidation reaction of NO to NO2 is
facilitated by radicals formed during hydrocarbon
(HC) oxidation; so-called “mutually sensitized”
oxidation of NO and HCs.
• This reaction may occur in a diesel vehicle
aftertreatment system due to the co-existence of
O2, HCs and NO.
• Studies that use the low temperature combustion
of diesel (LTC-D) protocol by US DRIVE should
consider such reaction.
• This work illustrates the intermediate that
facilitates NO to NO2 oxidation in a diesel vehicle
aftertreatment system.
NO is oxidized along with HCs
oxidation in full LTC-D mixture
DFT calculations suggest
initiating steps and radicals
responsible for NO oxidation
Acknowledgements
UT-Battelle, LLC, contract No. DE-
AC0500OR22725 with the U.S. Department of
Energy
Experiments400 ppm H2 2000 ppm CO 100 ppm NO
500 ppm C2H4 300 ppm C3H6 100 ppm C3H8
2100 ppm n-C10H22 Ar balance (HCs on C1-basis)
Reaction: 100-500oC (ramp rate = 2oC/min)
• As the temperature increased to 330oC, NO
began to sharply convert to NO2, arriving a
minimum concentration of 0 ppm at 340oC.
• Simultaneously, NO2 concentration increased to
a maximum concentration of 100 ppm at 340oC.
• Meanwhile, HC oxidation takes place. Increase
in C3H8 and CO concentration suggests they are
products of a reaction.
Reaction with individual HCs
shows that n-C10H22 is most
responsible for NO oxidation
Simplified reaction (NO+O2+
n-C10H22) reveals the species
formed during mutual
oxidation
• NO is completely consumed at 330oC.
• The majority of
HCs,
oxygenates and
N-containing
species formed
were detected.
H abstraction of n-C10H22
r7 n-C10H22 + O2 → ·C10H21 + ·HO2 1.77-1.98
eV
r8 n-C10H22 + ·H → ·C10H21 + H2 -0.66-
-0.45 eV
r9 n-C10H22 + ·OH → ·C10H21 + H2O -1.04-
-0.84 eV
Recombination
r10 ·C10H21 +O2 → ·C10H21O2 -0.10-
-0.03 eV
r11 ·H+O2→ ·HO2 -1.39 eV
r12 ·H+O2 → :O + ·OH 1.25 eV
r13 ·H+·H→H2 -3.91 eV
NO to NO2 oxidation
r14 NO+ ·HO2 → NO2+ ·OH -0.45 eV
r15 NO+ ·C10H21O2 → NO2+ ·C10H21O -0.98-
-0.93 eV
r16 2NO +O2 → 2NO2 -0.82 eV
• H abstraction is more thermodynamically
favored compared to unimolecular
decomposition for the consumption of n-
C10H22.
• Both the ·HO2 and ·C10H21O2 radicals oxidize
NO.
• NO oxidation by ·C10H21O2 is most favored.
• Only in the presence
of n-C10H22, NO to
NO2 occurred below
350oC, suggesting its
contribution in the full
mixture experiment.
NO
CO H2
O2
CO
2
Ar
EXHAUST
Syringe Pump
20
0°C
Fu
rnac
e
MFC
MFC
MFC
MFC
MFC
MFC
MFC
MFC
MFC
P
Dilution
Reactor
C2
H4
MFC
C3
H6
MFC
0oC
MFC
C3
H8
MFC
330oC330oC
330oC 330oC
330oC 330oC
Unimolecular decomposition of n-C10H22
r1 n-C10H22 → ·C10H21 + ·H 3.16-3.36
eV
r2 n-C10H22 → ·C9H19 + ·CH3 2.51 eV
r3 n-C10H22 → ·C8H17 + ·C2H5 2.46 eV
r4 n-C10H22 → ·C7H15 + ·C3H7 2.47 eV
r5 n-C10H22 → ·C6H13 + ·C4H9 2.45 eV
r6 n-C10H22 → 2·C5H11 2.48 eV
• C and N balance displays the species produced
during oxidation including smaller HCs,
oxygenates, HNO2, etc.
• De-greened catalysts
Hydrothermally Stable Pd and Pt/CeO2(core)@ZrO2(shell) Catalysts for Low
Temperature TWC ApplicationsChih Han Liu1, Todd J. Toops2 and Eleni A. Kyriakidou1,*
1Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA
2National Transportation Research Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
*Email: [email protected] (Eleni A. Kyriakidou)
• CeO2@ZrO2 is more thermally stable and has a higher OSC that lead
to lower T50’s under stoichiometric conditions.
• De-greened Pd/CeO2@ZrO2 and Pd/CeO2 (sphere) showed lower
T50,90’s compared to Pd/CeO2 (commercial).
• Catalysts deactivated after hydrothermal aging; Pd/CeO2
(commercial) showed comparable T90’s and higher T50’s compared to
Pd/CeO2 (sphere) and Pd/CeO2@ZrO2, suggesting the potential of
developing efficient CeO2@ZrO2-supported catalysts
Introduction
• Future three-way catalysts (TWC) will need to perform
effectively at increasingly low exhaust temperatures (150ºC
challenge).
• This work illustrates the potential of developing Pd-based
oxidation catalysts with enhanced low-temperature activity
using CeO2(core)@ZrO2(shell) supports.
Catalyst Preparation
Acknowledgements
Temperature/Time
De-greening (DG) 700°C/4hr
Pretreatment 600°C/20 min
Reaction 100-500°C (Ramp rate = 2°C/min)
Aging 800°C/10hr
O2
(%)
CO2
(%)
H2O
(%)
De-greening 0 10 10 -
Pretreatment 0 13 10 -
Reaction 0.74 13 10Simulated Gasoline
Exhaust*
Aging - 5 5
Lean/Rich cycling
(0.1 Hz)
Lean: 5% O2
Rich: 3% CO, 1% H2
Experiments
*1670 ppm H2 5000 ppm CO 1000 ppm NO
700 ppm C2H4 1000 ppm C3H6 300 ppm C3H8
1000 ppm i-C8H18 Ar balance (HCs on C1-basis)
GHSV: 130,000 h-1
• *Evaluated at 550oC.
• **Commercial CeO2 (Sigma-Aldrich) was used as a reference sample.
• CeO2@ZrO2 has an enhanced surface area upon thermal treatment
up to 900oC compared to commercial CeO2.
• Impregnation with Pd(NO3)2·4NH3.
• Supports and final catalysts: dried at 100ºC overnight and calcined at
500ºC/2h.
NO
CO Ar
EXHAUST
Syringe Pump
20
0°C
Fu
rnac
e
MFC
MFC
MFC
MFC
MFC
MFC
MFC
MFC
MFC
P
Dilution
Reactor
C2H
4M
FC
C3H
6M
FC
0o
MFC
C3H
8M
FC
CO
2
O2
H2
Calcined
500oC/2h
Calcined
700oC/2h
Calcined
900oC/2h
SA
m2/g
PV
cm3/g
SA
m2/g
PV
cm3/g
SA
m2/g
PV
cm3/g
Commercial CeO2** 2.8 0.006 2.5 0.006 3.3 0.007
CeO2@ZrO2 95.0 0.079 52.2 0.096 14.9 0.076
Pd/CeO2(sphere)Pd/CeO2(commercial) Pd/CeO2@ZrO2
Oxygen
Storage
Capacity*
(µmol/g)
Oxygen
Storage
Capacity
Complete*
(µmol/g)
Commercial CeO2**
0.3 0.7
CeO2 (sphere) 1.5 2.0
CeO2@ZrO2 10.2 10.7
Pd/CeO2@ZrO2 outperforms Pd/CeO2
(commercial) and Pd/CeO2 (sphere)
Hydrothermally aged Pd/CeO2 (sphere)
and Pd/CeO2@ZrO2 have lower T50’s
compared to Pd/CeO2 (commercial)• Hydrothermally aged catalysts
Pd/CeO2(sphere)Pd/CeO2(commercial) Pd/CeO2@ZrO2
UT-Battelle, LLC, contract No. DE-AC0500OR22725 with the U.S.
Department of Energy
CO THC NOx CO THC NOx
Hydrothermally agedDe-greened
Conclusions