Estimating the temperatures of the precious metal sites on a lean NOx trap during oxidation reactions

The temperatures of the platinum sites on a 0.64 cm long monolithic platinum/potassium/alumina lean NOx trap have been estimated during CO oxidation from the conversion of a trace amount of hydrocarbon (HC) and a HC conversion versus temperature calibration curve. The base exhaust contained 5% O2, 10% H2O, 10% CO2, and 200 ppm of the HC in N2. For CO levels of 2 to 5%, CO injection times of 5 to 180 s, and base temperatures of 300 to 500 °C, the inferred platinum site temperatures were in good agreement with tracer gases of propane, butane, hexane, and methane (when used), even though the levels of HC conversion were significantly different. At a base temperature of 300 °C with 2% CO, the steady-state precious metal temperature was approximately 130 °C higher than the temperature of the exhaust gas exiting the catalyst. The difference in PGM temperature and gas temperature decreased with increasing base temperature and increasing CO level, suggesting that radiation is an important mechanism of heat transfer within a catalyst during exothermic reactions.