초록 ▼

A two-stage catalyst comprises an oxidative first stage and a reductive second stage. The first stage is intended to convert NO to NO.sub.2 in the presence of O.sub.2. The second stage serves to convert NO.sub.2 to environmentally benign gases that include N2, CO2, and H.sub.2 O. By preconverting NO

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

대표청구항 ▼

[ The invention claimed is:] [1.] A method for reducing nitrogen oxides (NO.sub.x) in engine exhausts from oxygen-rich, high-temperature combustion, the method comprising the steps of:converting substantially all NO in an oxygen-rich engine exhaust with a first stage oxidizing catalyst to an interme

[ The invention claimed is:] [1.] A method for reducing nitrogen oxides (NO.sub.x) in engine exhausts from oxygen-rich, high-temperature combustion, the method comprising the steps of:converting substantially all NO in an oxygen-rich engine exhaust with a first stage oxidizing catalyst to an intermediate gas flow including NO.sub.2 ;adding hydrocarbons into the intermediate gas flow; andconverting substantially all of said intermediate gas flow including NO.sub.2 in the presence of hydrocarbons with a second-stage selective catalytic reduction (SCR) catalyst to an output gas flow comprising NO.sub.2 conversion products of N.sub.2, CO.sub.2 and H.sub.2 O and substantially little NO and NO.sub.2 (NO.sub.x);wherein, the first stage oxidizing catalyst is used to convert NO to NO.sub.2 and then the second-stage selective catalytic reduction (SCR) catalyst is used to convert NO.sub.2 and the hydrocarbons to N.sub.2, CO.sub.2, and H.sub.2 O.