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 C3H6 + 9 NO  3 CO2 + 3 H2O + 4.5 N2 C3H6 + 4.5 O2 ↔ 3 CO2 + 3 H2O C3H6 + 3 O2 ↔ 3 CO + 3 H2O C3H6 + 4 NO2 ↔ 3 CO + 3 H2O + 2N2O C3H6 + 4.5 NO2 ↔ 3 CO2 + 3 H2O + 2.25 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, 50-150°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.15793. 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: 400-1800ppm C3H6, 2% O2, 5°C/min