Carbon monoxide-selective oxidation catalysts

A method of removing carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) from an exhaust stream of an internal combustion engine that is configured and controlled to primarily operate fuel-lean, but also to periodically operate fuel-rich to generate ammonia (NH3) in the exhaust stream, the method comprising:

• controlling the engine during fuel-rich operation so that the exhaust stream from the engine contains nitrogen oxides (NOx), carbon monoxide (CO), and hydrogen (H2), but little or no oxygen (O2);
• passing the exhaust stream from the engine in contact with particles of a platinum group metal (PGM) catalyst to convert an amount of NOx, CO, and/or H2 in the exhaust stream to ammonia (NH3);
• and thereafter
• adding oxygen to the exhaust stream and passing the exhaust stream in contact with particles of a CO-selective oxidation catalyst to oxidize CO in the exhaust stream to carbon dioxide (CO2) without oxidizing the NH3, the CO-selective oxidation catalyst comprising particles of mixed oxides of cerium (Ce), zirconium (Zr), and copper (Cu).

An exhaust treatment system for removing carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) from an exhaust stream of an internal combustion engine that is configured and controlled to primarily operate fuel-lean, but also to periodically operate fuel-rich to generate ammonia (NH3) in the exhaust stream, the system comprising:

• a platinum group metal (PGM) catalyst;
• a carbon monoxide (CO)-selective oxidation catalyst comprising particles of cerium (Ce), zirconium (Zr), and copper (Cu) mixed oxides;
• an oxygen dosing device for periodically dosing the exhaust stream with oxygen, the oxygen dosing device being located upstream of the CO-selective oxidation catalyst and downstream of the PGM catalyst, relative to a flow path of the exhaust stream from the engine;
• and
• at least one NH3-SCR catalyst located downstream of the PGM catalyst and the CO-selective oxidation catalyst, relative to the flow path of the exhaust stream from the engine.