Enabling Wide-Temperature Selective Catalytic Reduction of NO_X via Modulating Redox Ability of Mn-Based Catalysts

Abstract

Nitrogen oxides (NO X ) emitted from marine diesel engines have appealed for efficient catalysts with a wide operation window for selective catalytic reduction of NO X by NH 3 (NH 3 -SCR). However, challenges in the balance between the redox sites and proper acidic sites on the surface of catalysts restricted the development of wide-temperature range NH 3 -SCR catalysts. Herein, we reported a facile method to manipulate the redox ability of MnOx to improve the low-temperature SCR activity. The modified MnOx catalysts (MnOx-350-air + NH 3 ) exhibited above 80% NO conversion and 100% selectivity to N 2 in a wide temperature range from 150 to 500 °C (NO = NH 3 = 1000 ppm, O 2 = 7%, GHSV = 7200 h −1 ) and showed higher water resistance ability than the counterpart MnOx precursor catalyst. XPS and H 2 -TPR results revealed that the redox capability was improved significantly by changing the ratio of Mn 4+ /Mn n and O α /(O α +O β ), resulting in the promotion of the adsorption and oxidation of NO to facilitate "fast SCR". NH 3 -TPD results revealed that the preparation method could controllably adjust the redox ability of catalysts without affecting the amount of B acid sites on their surface. This work might provide insight into the deliberate design of catalysts with a wide operating window for controlling NOx.