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New ORNL non-precious metal catalyst shows promise as low-cost component for low-temperature exhaust aftertreatment

Researchers at Oak Ridge National Laboratory (ORNL) have developed a ternary mixed oxide catalyst composed of copper oxide, cobalt oxide, and ceria (dubbed “CCC”) that outperforms synthesized and commercial platinum group metal (PGM) catalysts for CO oxidation in simulated exhaust streams while showing no signs of inhibition—i.e., the clogging of the catalyst by NOx, CO and HC.

PGM catalysts are the current standard for emissions aftertreatment in automotive exhaust streams. However, in addition to their high cost, PGM catalysts struggle with CO oxidation at low temperatures (<200 °C) due to inhibition by hydrocarbons in exhaust streams. The new ORNL catalyst shows great potential as a low-cost component for the low temperature exhaust streams that are expected to be a characteristic of future automotive systems, the researchers noted in their paper in the journal Angewandte Chemie.

Our catalyst potentially fixes the inhibition problem without precious metals and could help more efficient engines meet upcoming stricter emission regulations.

—Todd Toops of ORNL’s Energy and Transportation Science Division

Toops noted that the unique ORNL formulation builds on previous work by colleagues Andrew Binder and Sheng Dai, who varied the composition of the three catalyst components in search of improved oxidation activity under simple conditions.

Researchers also emphasized that the lower exhaust temperatures associated with efficiency gains pose additional challenges because conventional catalysts perform more efficiently at high temperatures. The hundreds of species of hydrocarbons pose perhaps the biggest challenge.

As we make engines more efficient, less wasted heat exits the engine into the exhaust system where catalysts clean up the pollutant emissions. The lower temperatures in the exhaust from the more efficient engines are lower than the typical operating range of catalysts, so we need innovations like this catalyst to lower the operating range and control the engine pollutants.

—Jim Parks, a member of the Energy and Transportation Science Division

This finding is encouraging, the authors noted in their paper, as “vehicles with internal combustion engines will likely remain a dominant fraction of the light-duty fleet in both hybrid and conventional drivetrains.

Binder, Toops, Parks and Dai performed extensive tests using different ratios of copper oxide, cobalt oxide and ceria to determine the optimum ratio, which was initially evaluated at an atomic ratio of 1:5:5, respectively. Next, researchers will determine scalability of this approach and perform cost-benefit analyses.

DOE’s Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program, funded this research.

Resources

  • Binder, A. J., Toops, T. J., Unocic, R. R., Parks, J. E. and Dai, S. (2015), “Low Temperature CO Oxidation over a Ternary Oxide Catalyst with High Resistance to Hydrocarbon Inhibition,” Angew. Chem.. doi: 10.1002/ange.201506093

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