Carbon monoxide-selective oxidation catalysts

摘要

Particles of mixed oxides of cerium, zirconium, and copper (CeZrCuOX) may be prepared as catalysts and used to preferentially catalyze the oxidation of CO in exhaust streams containing CO and NH3. In one practice, this CeZrCuOX catalyst may be used in combination with a close-coupled PGM catalyst which promotes the formation of NH3 in the exhaust during fuel-rich operation, and at least one under-floor NH3-SCR catalyst, which catalyzes the reduction of NOX in the exhaust stream during fuel-lean operation using NH3 as a reductant. During fuel-rich engine operation, the exhaust stream may be doped with oxygen downstream of the PGM catalyst and passed in contact with particles of the CeZrCuOX catalyst so that residual CO in the exhaust may be oxidized to CO2, without oxidation or other conversion of the NH3.

主权项

1. A method of removing carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NX) from an exhaust stream of an internal combustion engine that is powering an automotive vehicle, the engine being 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 (NX), 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 NX, 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), the mixed oxides of cerium, zirconium, and copper consisting of CeaZrbCucOx, which is formulated such that a has a value in the range of 0.50 to 0.70, b has a value in the range of 0.10 to 0.20, and c has a value in the range of 0.15 to 0.35, with the sum of these molar ratios of Ce, Zr, and Cu being equal to 1, and the value of x is in the range of one to three.