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Physical Sciences
Research Highlights

June 2015

The Shorter Road to Having It All: Fuel Efficiency and Cleaner Exhausts

Five scientists review the state of research on two catalysts that can work in lean-burn engines

Zeolites and nitrogen oxides
Experts from Pacific Northwest National Laboratory and University College London analyzed the state of the science and future research directions of two highly efficient, heat-stable catalysts for nitrogen oxides conversion. Enlarge Image

Lean-burn engines operate under net oxidizing conditions to improve fuel efficiency by more than 25 percent, compared to conventional engines. Unfortunately, the added air causes the performance of conventional exhaust emission systems to deteriorate as the reduction of nitrogen oxides into harmless nitrogen is suppressed. The presence of nitrogen oxides (commonly abbreviated NOx) in the atmosphere can lead to smog, a health risk. For about 5 years, scientists have studied two extremely heat-stable, highly efficient catalysts for NOx conversion: Cu-SSZ-13, a zeolite material, and the isostructural Cu-SAPO-34.

Recently, scientists at Pacific Northwest National Laboratory and University College London analyzed the state of the science and future research directions of these catalysts in an extensive review article.

The team was chosen because each scientist is a key player in automotive exhaust control catalysis research: Dr. Charles HF Peden and Dr. Janos Szanyi were members of the PNNL team that wrote the first publicly accessible paper on the high lean NOx reduction activity of Cu-SSZ-13, and Dr. Feng Gao has been instrumental to the synthesis and kinetic characterization of these catalysts in the past 4 years. Dr. Andrew Beale and Dr. Ines Lezcano-Gonzalez at UCL have done pioneering catalyst characterization work, which began shortly after the PNNL paper appeared.

In the 35-page review, the five authors discuss the current state of knowledge regarding the structure activity relationships of the two copper-based catalysts. They summarize the key findings on catalytic performance and efficacy studies that are providing new insights into how the catalysts can transform NOx and retain their performance even after high-temperature excursions. At the end of the review they also discuss issues that need to be addressed in future studies.

The researchers are continuing to delve into the challenges of removing pollutants from the exhaust pipes of the billion-plus cars running on the world's roads.

Acknowledgments

Sponsors: A.M.B. and I.L.G. received funding from the Engineering and Physical Sciences Research Council. F.G., C.H.F.P., and J.S. were funded by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program.

Research Area: Chemical Sciences

Research Team: Andrew M Beale, University College London and UK Catalysis Hub; Ines Lezcano-Gonzalez, University College London; Feng Gao, Charles HF Peden, and Janos Szanyi, PNNL

Reference: Beale AM, F Gao, I Lezcano-Gonzalez, CHF Peden, and J Szanyi. 2015. "Recent Advances in Automotive Catalysis for NOx Emission Control by Small-Pore Microporous Materials." Chemical Society Reviews. Article online. DOI: 10.1039/c5cs00108k


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Catalyst 101

Not all catalysts are created equal, so understanding the fundamental chemistry of catalytic reactions is critical for developing the most efficient and effective materials. Catalysts are materials that help chemical reactions take place rapidly and efficiently without being used up in the reaction. Essentially, they "loan" a part of their molecular structure to the reaction and then return to their original state when the reaction is complete. Catalysts are used in many processes, including pharmaceutical manufacturing, oil refining, and next-generation biofuels.
-- Courtesy of Kathryn Lang

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