Treatment of Natural Gas Vehicle Exhaust

The objective of this study is to investigate the removal of methane (CH₄), nitric oxide (NO), and carbon monoxide (CO) from simulated natural gas vehicle (NGV) exhaust over a palladium catalyst. The effects of changes in space velocity and natural gas sulfur (S) content were studied. The study suggests that the NGV has to be operated slightly rich of stoichiometry to achieve simultaneous removal of the three constituents. The CH₄ conversion decreases with an increase in the space velocity. The CO and NO conversions remain unaffected over the space velocity range (10,000 hr^-1 to 100,000 hr^-1) investigated. The presence of sulfur dioxide in the exhaust lowers the CH₄ conversion and increases the CO conversion in the rich region. The NO conversion remains unaffected. Studies were conducted over model catalysts to investigate the modes of CH₄ removal from the simulated NGV exhaust. These investigations suggest that CH₄ is oxidized by O₂ in the lean region and by NO and O₂ in the rich region.