| abstract |
A method of decomposing NO to NO in an exhaust gas of a lean-bum internal combustion engine comprises the steps of contacting an acidic metal oxide selected from the group consisting of zeolites, tungsten-doped titania, silica-titania, zirconia-titania, gamma-alumina, amorphous silica-alumina and mixtures of any two or more thereof with a gas mixture comprising the exhaust gas, adjusting the composition of the gas mixture, by injecting hydrocarbon therein at a rate that changes over the course of a duty cycle so that, on average over the duty cycle, the Cl hydrocarbon : nitrogen oxides ratio of the gas mixture contacting the acidic metal oxide is from 0.1 to 2.0 and passing the effluent gas directly to atmosphere optionally via first contacting the gas mixture with a hydrocarbon oxidation catalyst. |