| abstract |
A two-stage catalyst comprises an oxidative first stage and a reductive second stage. The first stage is intended to convert NO to NO 2 in the presence of O 2 . The second stage serves to convert NO 2 to environmentally benign gases that include N2, CO2, and H 2 O. By preconverting NO to NO 2 in the first stage, the efficiency of the second stage for NO x reduction is enhanced. For example, an internal combustion engine exhaust is connected by a pipe to a first chamber. An oxidizing first catalyst converts NO to NO 2 in the presence of O 2 and includes platinum/alumina, e.g., Pt/Al 2 O 3 catalyst. A flow of hydrocarbons (C x H y ) is input from a pipe into a second chamber. For example, propene can be used as a source of hydrocarbons. The NO 2 from the first catalyst mixes with the hydrocarbons in the second chamber. The mixture proceeds to a second reduction catalyst that converts NO 2 to N2, CO2, and H 2 O, and includes a gamma-alumina γ-Al 2 O 3 . The hydrocarbons and NO x are simultaneously reduced while passing through the second catalyst. |