Technical Paper
Aged DOC is a Net Consumer of NO2: Analyses of Vehicle, Engine-dynamometer and Reactor Data
2007-10-29
2007-01-3984
A typical diesel After-Treatment (AT) system to meet 2010 North American regulations consists of a Diesel Oxidation Catalyst (DOC) for oxidizing Hydrocarbons (HCs) and Carbon Monoxide (CO), followed by a Selective Catalytic Reduction (SCR) catalyst for NOx reduction, and a diesel particulate filter. DOCs are also used to oxidize NO in the exhaust to NO2 that substantially improves low-temperature SCR NOx reduction performance. Vehicle and engine dynamometer data under typical operating conditions show (1) engine-out NO2/NOx can be as high as 40%, (2) DOC can reduce NO2 to NO in the presence of reductants, and (3) an aged DOC with a low CO/HC conversion can be a net consumer of NO2 over a wide range of temperatures and space velocities. Flow reactor experiments simulating diesel exhaust conditions show that DOC-out NO2 is independent of the inlet NO2/NOx in the feed.
