Exhaust Catalyst Traps And Scrubs NO_x

Automobile engines designed to combust fuel in a large excess of oxygen can achieve higher fuel efficiency than other common engines. But standard catalytic cleanup technology cannot readily scrub (chemically reduce) the nitrogen oxides (NO and NO₂, or NO_x) in the exhaust of these so-called lean-burn engines because of the overwhelming excess of O₂. A research team led by Hui Xian of Tianjin University, in China, has demonstrated that NO_x can be scrubbed effectively by using a palladium-doped LaSrCoO₃ material to trap and treat the pollutants (ACS Catal. 2013, DOI: 10.1021/cs400136t). The method works by oxidizing NO_x compounds in excess O₂ and trapping them as nitrates. The nitrates are periodically purged and reduced by hydrocarbons, which are deliberately generated by briefly switching the engine from a fuel-lean to a fuel-rich mode. In contrast to previously studied lean NO_x trap materials, the new compound resists sulfur poisoning and does not depend on costly platinum. In addition, lean NO_x trap technology could be simpler and smaller than an alternative NO_x treatment method that requires carrying an onboard tank of a reductant such as urea.