Patent ID: 8092767

Claim:
A method of decomposing nitrogen dioxide (NO 2 ) to nitrogen monoxide (NO) in an exhaust gas of a lean-burn internal combustion engine, which method comprising: adjusting the C1 hydrocarbon:nitrogen oxides (C1 HC:NO x ) ratio of the exhaust gas to from 0.1 to 2; contacting the gas mixture from the adjusting step with a particulate acidic refractory 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, wherein nitrogen dioxide (NO 2 ) present in the gas mixture is converted to nitrogen monoxide (NO); and passing the effluent gas from the contacting step to atmosphere.