Exceptional activity for NOx reduction at low temperatures using combinations of hydrogen and higher hydrocarbons on Ag/Al2O3 catalysts

The effect of the addition of hydrogen on the SCR of NOx with a hydrocarbon reaction was investigated. It was found that hydrogen had a remarkable effect on the temperature range over which NO,. could be reduced during the SCR reaction with octane. Reduction of NOx was initiated at as low a temperature as 100 degreesC and > 95% NOx conversion was achieved over a temperature range of 200-450 degreesC. Hydrogen has the effect of activating octane at lower temperatures and also promotes the oxidation of NO to NO2 in the absence of hydrocarbon. Transient kinetic and in situ DRIFTS measurements indicated that hydrogen has a direct role in the reaction mechanism by either promoting the formation and storage of an organic C=N species which can then readily reduce NOx and/or removing a species which acts as a poison to the SCR reaction at low temperatures.