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Small-pore zeolite supported Pd and Pt as passive NOx adsorbers and low-temperature methane combustion catalysts

EMSL Project ID


To help meet DOE goals of enabling more fuel-efficient vehicle engine technologies, for the past ~15 years we have been carrying out research programs funded by DOE/Office of Energy Efficiency and Renewable Energy (EERE)/Vehicle Technologies Office (VTO), involving programs that include direct collaboration with industry partners in the form of CRADA programs, and more fundamental programs directly funded by VTO. Currently, the industry-partner CRADA program with Cummins, Inc. aims at lowering NOx emission during vehicle cold start by invoking novel passive NOx adsorber (PNA) materials. The program directly funded by VTO to PNNL is aimed at developing a practically useful fundamental understanding of low-temperature methane combustion catalysts as part of the natural gas engine exhaust abatement strategy. For both programs to be successful, we rely on the use of a wide array of state-of-the-art catalyst characterization facilities in the EMSL at PNNL. This approach of coupled fundamental studies and more applied studies with industry partners has been highly successful. Our group published 22 peer-reviewed publications during 2015-2017 from our prior VT programs, acknowledging the essential support from EMSL. We anticipate to continue high productivity success with continuous EMSL support.
A promising approach to address cold-start NOx emission is to employ a passive NOx adsorber (PNA) material upstream of the main catalytic convertor (TWC or SCR). Efficient PNA is designed to adsorb NOx, preferably NO, during the cold-start period. The stored NOx should then be readily released once the TWC/SCR system becomes operational. In contrast to the LNT catalyst that only adsorbs NO2 and requires periodical chemical reduction via rich purging to release stored NOx, the PNA thermally releases NOx under continuous lean conditions at higher temperatures, e.g., 200?350 °C, where the catalytic convertor functions efficiently. Recently, Pd-exchanged zeolite materials have been discovered as potential industrial PNA materials, showing good NOx trapping efficiency and proper releasing temperatures. However, since these zeolite-based materials are so newly recognized, little is known about the nature of active Pd species responsible for optimized NOx adsorption/release. Even less is known about the long-term durability of these materials, i.e., hydrothermal stability and tolerance to sulfur poisoning. For the program directly funded by DOE/EERE/VT to PNNL on low-temperature methane combustion, supported Pd, Pt and alloy catalysts containing one of the two metals will be investigated. Among which, small-pore zeolite supported Pd catalysts will be one of the main focuses since recently we have discovered their high turnover rates and long-term stability in our preliminary investigations. Again, since these materials are so newly developed, extensive spectroscopic and microscopic investigations are required to gain atomic-level knowledge of the nature of the active sites and their local environments.

To realize the proposed research goals, we request the following state-of-the-art EMSL instrument, including NMR, XPS, FTIR, SSITKA, TEM, STEM, SEM (or HIM), XRD and APT (instrument time and EMSL staff support requests detailed in the proposal) and 300,000 supercomputer node hours.

Project Details

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Principal Investigator

Feng Gao
Pacific Northwest National Laboratory

Team Members

Yanran Cui
University of Washington

Konstantin Khivantsev
Pacific Northwest National Laboratory

Yilin Wang
Pacific Northwest National Laboratory

Miroslaw Derewinski
Pacific Northwest National Laboratory

Donghai Mei
Tiangong University

Janos Szanyi
Pacific Northwest National Laboratory

Yong Wang
Washington State University

Related Publications

Khivantsev K., F. Gao, L. Kovarik, Y. Wang, and J. Szanyi. 2018. "Molecular Level Understanding of How Oxygen and Carbon Monoxide Improve NOx Storage in Palladium/SSZ-13 Passive NOx Adsorbers: The Role of NO+ and Pd(II)(CO)(NO) Species." Journal of Physical Chemistry C 122, no. 20:10820-10827. PNNL-SA-131978. doi:10.1021/acs.jpcc.8b01007