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Summary
The emission of nitric and nitrous oxides (NOx) is a major cause of unhealthful air quality and is strictly regulated in many places. To meet regulations, exhaust gases from power plants, ships, trucks, and passenger cars are passed through catalytic cleaning systems designed to remove the harmful carbon monoxide, unburnt hydrocarbons, soot, and NOx before emission to the atmosphere. For gasoline engines, a “three-way” catalyst removes all harmful compounds, but such catalysts cannot be applied in the oxygen-rich environment in diesel exhausts. A class of catalysts for NOx reduction in diesel exhausts are copper (Cu) zeolites, which reduce the NOx with added ammonia and oxygen, so as to form unharmful nitrogen and water through selective catalytic reduction (SCR) (1, 2). Such catalysts are already deployed in diesel engine exhaust systems. On page 898 of this issue, Paolucci et al. (3) show that the traditional view of active sites in Cu zeolites, a central concept in catalysis, is not sufficient to understand how they truly function.
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