Understanding NOx SCR Mechanisms and Activity on Cu/Chabazite Structures throughout the Catalyst Life Cycle
EMSL Project ID
48807
Abstract
This proposed EMSL use will enable research that has been recently funded at PNNL by the Department of Energy (DOE), and at the remainder of the partner institutions by a joint DOE/National Science Foundation (NSF) program. For this recently funded research, the PIs provide a team with a wealth of experience in both the application and science of heterogeneous catalysis, especially as related to NOx chemistry, and with outstanding expertise in the diverse tools necessary to achieve the objectives of the proposed studies.The selective catalytic reduction (SCR) with ammonia on Cu- and Fe-exchanged chabazite (CHA) zeolites is the state-of-the-art for lean NOx reduction in excess oxygen and thus enables access to the fuel efficiency of lean burn engines. Although these materials are used commercially, their structure and catalytic behavior changes in unpredictable ways as they respond to varying SCR reaction conditions and in particular as they accumulate sulfur species that cause deactivation. To dramatically improve today's materials, to optimize engine efficiency within emission constraints, and to circumvent deactivation, a microscopically detailed model of catalyst performance under all operating conditions and through the life cycle is essential.
Cu/CHA and Fe/CHA catalysts present multiple and dynamic active site functionalities that contribute to overall activity and deactivation. Our synthetic capability to vary framework Al density and influence Cu and Fe distributions between the six- and eight-ring structures in CHA, to prepare zeolites with similar six- and eight-ring structures, and to widely vary Al, Fe and Cu content will provide a set of materials that emphasize specific local active site structures for comparison. Detailed kinetic analysis and unique operando characterization of the Cu and Fe will be obtained using EMSL EPR and Mossbauer spectrometers, and with synchrotron x-ray absorption spectroscopy (XAS) at another DOE user facility, the Advanced Photon Source at Argonne National Laboratory. A critical characterization tool will be with solid-state NMR which will be especially useful for characterizing Al distributions in the synthesized zeolites. Instrumentation in EMSL and in some of the PI's home laboratories will be used to obtain information on kinetically important intermediates with FTIR and isotopic switching, using methods developed by members of this team. DFT models will be implemented on the EMSL supercomputer to determine the structure, spectroscopies, and thermodynamic stability of candidate sites vs. local structure, and to identify reaction intermediates, steps and rates. As relationships between structure and catalytic behavior are identified, they will be used to set synthetic targets for new materials with active site distributions that optimize catalytic performance and robustness. Thus, our proposed approach brings to bear the full arsenal of modern catalysis science techniques, including a number of methods uniquely available to the catalysis science community via the EMSL user facility, to bear on a problem of great societal importance.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2015-10-01
End Date
2017-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members
Related Publications
Cui Y., Y. Wang, D. Mei, E.D. Walter, N.M. Washton, J.D. Holladay, and Y. Wang, et al. 2019. "Revisiting effects of alkali metal and alkaline earth co-cation additives to Cu/SSZ-13 selective catalytic reduction catalysts." Journal of Catalysis 378. PNNL-SA-141699. doi:10.1016/j.jcat.2019.08.028
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Hensley, A. J. R., Therrien, A. J., Zhang, R., Marcinkowski, M. D., Lucci, F. R., Sykes, E. C. H., & McEwen, J.-S. (2016). CO Adsorption on the ?29? Cu xO/Cu(111) Surface: An Integrated DFT, STM, and TPD Study. The Journal of Physical Chemistry C, 120(44), 25387?25394. http://doi.org/10.1021/acs.jpcc.6b07670
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Szanyi J, F Gao, JH Kwak, M Kollar, Y Wang, and CHF Peden. 2016. "Characterization of Fe2+ Ions in Fe,H/SSZ-13 Zeolites: FTIR Spectroscopy of CO and NO Probe Molecules." Physical Chemistry Chemical Physics. PCCP 18(15):10473-10485. doi:10.1039/c6cp00136j
Therrien A J,Zhang R ,Lucci F R,Marcinkowski M D,Hensley A ,McEwen JS ,Sykes EC H 2016. "Structurally Accurate Model for the “29”-Structure of CuxO/Cu(111): A DFT and STM Study" Journal of Physical Chemistry C 120(20):10879–10886. 10.1021/acs.jpcc.6b01284
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Zhang R., E. Anderst, K.J. Groden, and J. McEwen. 2018. "Modeling the Adsorption of NO and NH3 on Fe-SSZ-13 from First-Principles: A DFT Study." Industrial and Engineering Chemistry Research 57, no. 40:13396–13405. doi:10.1021/acs.iecr.8b03643
Zhang R, KA Helling, and JS McEwen. 2016. "Ab Initio X-ray Absorption Modeling of Cu-SAPO-34: Characterizationof Cu Exchange Sites Under Different Conditions." Catalysis Today 267:28-40. doi:10. 1016/j. cattod. 2016. 01. 025