Two-Stage Catalytic NOx Reduction With Hydrocarbons for Lean Burn Gas Fired Reciprocating Engines

A two-stage NOx reduction system has been proposed to address the challenges associated with exhaust treatment from high efficiency lean burn natural gas engines. This concept is based on oxidation of NO to NO₂ followed by the subsequent reduction of NO₂ to N₂ with a hydrocarbon reducing agent. Titania supported cobalt catalysts prepared by both incipient wetness and modified sol-gel techniques are effective for the oxidation of NO to NO₂, being capable of reaching equilibrium conversions at or below 300°C. Screening of several formulations of NO₂ reduction catalysts are presented, with silver supported on alumina being the most promising. Kinetic experiments are monitored by gas chromatography and chemiluminescent NO_x analysis. Characterization of the catalysts is performed by BET surface area measurements, thermogravimetric analysis, and in-situ X-ray diffraction.