Selective catalytic reduction of NOₓ in marine engine exhaust gas over supported transition metal oxide catalysts

Abstract

The selective catalytic reduction (SCR) of nitrogen oxides (NOx) in the presence of methanol (methanol-SCR) was investigated over commercial oxide (γ-Al2O3 and TiO2) supported transition-metal oxide catalysts in lab scale. Of all the prepared catalysts, CuO/γ-Al2O3 catalyst exhibited the highest reduction efficiency in the methanol-SCR process. The practical test results in a marine engine further showed that the 2 wt% CuO/γ-Al2O3 catalyst can remove 93.9% of NOx without catalyst deactivation in several hours. Evidenced by relevant characterization results, the fast-redox properties of copper and rich acidic sites of γ-Al2O3 support were responsible for the excellent catalytic activity of the CuO/γ-Al2O3 catalyst. Revealed by In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), formate-like species derived from methanol dehydrogenation act as the reaction intermediates for NOx reduction. Moreover, this work provides a novel process to reduce NOx and make use of adverse hydrocarbons in the flue gas simultaneously, opening a new research direction in NOx reduction technologies.