Cleaning Diesel Exhaust: One strategy for removing pollutants from diesel engine exhaust is to trap the unburned carbon soot and then to combust the soot with the NO ₂ that is generated from NO; the two pollutants are then converted to N ₂ and CO ₂ . Diesel exhaust is relatively cold, compared to gasoline engine exhaust, and conversion of NO to NO ₂ has required the use of platinum catalysts. W. Wang et al. (p. 832 ) now report that a more earth-abundant catalyst, based on Mn-mullite (Sm, Gd)Mn ₂ O ₅ metal oxides was able to oxidize NO in simulated diesel exhaust at temperatures as low as 75°C. Spectroscopic studies and quantum chemical modeling suggested that Mn-nitrates formed on Mn-Mn dimer sites were the key intermediates responsible for NO ₂ formation.