1. Coupled NO and C3H6 Trapping, Release and Conversion on Pd-BEA
Sam Malamis, Mugdha Ambast, Michael P. Harold, William S. Epling1
Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204
1Department of Chemical Engineering University of Virginia, Charlottesville, VA
Motivation
Proposed Mechanism
NO + C3H6 Co-adsorption
PdO  Pd2+ Distribution
PdO + 2H+Z- ↔ Z-Pd2+Z- + H2O
Complete Storage/Release Profile
NO: 60 μmol/g-cat
HC: 830 μmol/g-cat
Stringent requirements on fuel economy and emission standards are challenging to meet for both gasoline and diesel engine vehicles
A number of technologies including low temperature diesel combustion are in development for improving fuel economy, but produce higher amounts of NOx
Typical systems (TWC, LNT, SCR) are ineffective below ~200°C
Increased emissions during cold start
NOx/N2O Desorption
C3H6 inhibits NO adsorption (63% reduction)
NOx desorption peak shifts to the right
Fraction desorbing above 200°C increases from 52% to 86%
NO2 formed during ads./des. reduced by C3H6, also forms N2O
Product distribution depends on both acid site and Pd-catalyzed interactions
Multiple CO2 peaks caused by variations in light-off bahavior of HCs formed during adsorption
Objectives
Pd2+  Pd+ Oxidation - Reduction
2[PdOH]+Z- + NO ↔ 2Pd+Z- + NO2 + H2O
Z-[Pd-O-Pd]2+Z- + NO ↔ NO2 + 2Pd+Z-
Z-Pd2+Z-+ NO ↔ Z-Pd+(NO)+Z-
H2O + ½ O2 + 2Pd+Z- ↔ 2[PdOH]+Z-
C3H6 Adsorption and Oligomerization
H+Z- + C3H6 ↔ [H3C(CH)+CH3]+Z-
n[H3C(CH)+CH3]+Z- ↔ [H3C(CH)+(CH3)]n+Z-
Investigate a multifunctional catalyst with the following behavior
Trap NO and HC at temperatures below 200°C
Release NO and HC upon warm-up
Oxidize HC/CO to CO2
Further understanding of combined NO/HC trapping/release effectiveness
Develop mechanistic understanding of NO/HC storage and their inhibitive behavior
Evaluate the impact of water and investigate methods to improve storage
Formulate working model that can predict storage, release and oxidation behavior of PNA catalyst
Global Pd-Catalyzed Reactions
NO + ½ O2 ↔ NO2
2 NO  0.5 O2 + N2O
C3H NO  3 CO2 + 3 H2O N2
C3H O2 ↔ 3 CO2 + 3 H2O
C3H6 + 3 O2 ↔ 3 CO + 3 H2O
C3H6 + 4 NO2 ↔ 3 CO + 3 H2O + 2N2O
C3H NO2 ↔ 3 CO2 + 3 H2O N2
NO Adsorption and Other Reactions
Pd+Z- + NO ↔ NOPd+Z-
NO + ½ O2 + H+Z- ↔ [NO2 H] +Z-
[NO2 H] +Z- + ½ O2 ↔ [NO3 H] +Z-
2NO2 ↔ N2O4 ↔ NO+ + NO3-
H+Z- + NO+ + NO3-↔ NO+Z- + HNO3
Water Effects
NOx Adsorption
C3H6 Adsorption
Experimental Setup
H2O inhibits NO and C3H6 adsorption
Oxytreatment: 10% O2,bal. Ar at 750°C for 2hr [4]
C3H6 Adsorption, Desorption and Light-Off
Catalyst
2wt% Pd-BEA (SAR 38)
1.5g/in3 monolith (0.31g total)
400 cpsi
2500 sccm (32k hr-1)
Feed Conditions
All feeds contain 2% O2, bal. Ar
Adsorption Profile
Desorption Profile
Conditions: 400ppm NO or 800ppm C3H6 , 2% O2, 0 or 5% H2O, 80°C ads.
Ads. Temp. (°C)
Storage Time
NOin (ppm)
C3H6,in (ppm)
50°C, 80°C, 150°C
5 min
400 ppm
0 ppm
800 ppm
Conclusions & Future Work
Mechanism developed consistent with adsorption, desorption and reaction data
Significant findings include:
NO stores on both Pd and BEA acid sites through a number of interactions
C3H6 forms coupled products during adsorption, leads to the release of a complex distribution of hydrocarbons
NO and C3H6 uptake are mutually inhibitive due to competition for adsorption on Brønsted acid sites
C3H6 delays NO desorption to higher temperatures
High-temperature oxidation pretreatment improves NO uptake in presence of H2O
Upon warmup, PNA aids in oxidation of HC to CO2
Future work includes development of predictive kinetic model for Pd/BEA system
Future experimental work includes steady state and oxidation studies to evaluate kinetic parameters
Model development can be used to predict behavior of other Pd-based zeolites 80
NOx Storage
Conditions: 800ppm C3H6, 2% O2, °C ads., 20°C/min des.
Desorption profile provides evidence for C3H6 coupling
NO uptake decreases with temperature
NO2 formation during uptake suggests NO oxidation
Key step in NO storage
Multi-peak desorption indicates formation of various storage complexes
NO on BEA (low Temp.)
NO on Pd (high Temp.)
Adsorption Profile
Desorption Profile
C3H6 Light-Off Behavior
T50 vs. Feed C3H6
400ppm
800ppm
1200ppm
1600ppm
1800ppm
References
Acknowledgements
Y. Murata, T. Morita, K. Wada, H. Ohno, SAE Int. J. Fuels Lubr. 8 (2015) p.1.
H.-Y. Chen, J.E. Collier, D. Liu, L. Mantarosie, D. Durán-Martín, V. Novák, R.R. Rajaram, D. Thompsett, Catal. Letters. 146 (2016) p.1706.
Y. Zheng, L. Kovarik, M.H. Engelhard, Y. Wang, Y. Wang, F. Gao, J. Szanyi, J. Phys. Chem. C. 121 (2017) p
Y.S. Ryou, J. Lee, S.J. Cho, H. Lee, C.H. Kim, D.H. Kim, Appl. Catal. B Environ. 212 (2017) p.140.
Funding provided by:
FCA, Inc.
US DOE-EERE Vehicle Technologies Program
Conditions: 400ppm NO, 2% O2, 80°C ads., 20°C/min des.
Conditions: ppm C3H6, 2% O2, 5°C/min