Eu-Mn-Ti mixed oxides for the SCR of NOx with NH3: The effects of Eu-modification on catalytic performance and mechanism

A series of highly active de-NOx catalysts, Eu-modified MnOx-TiO2 (MnTiEu), was prepared by an inverse co-precipitation method. Their physiochemical properties were investigated by XRD, TEM, EDS, BET, XPS and H-2-TPR in detail, and their catalytic activities were evaluated by the selective catalytic reduction (SCR) of NO with NH3. The results showed that the introduction of Eu with proper amount into MnOx-TiO2 can effectively restrain the crystallization process of MnOx and TiO2, enhance specific surface area, increase the concentration of both surface Mn4+ and chemisorbed oxygen species, improve the stability of Mn4+ and Mn3+, reduce the amount of surface acid sites, enhance the strength of surface acid sites. The obtained MnTiEu-0.3 catalyst (the molar rate of Eu/Mn was 0.3 and the mole rate of Mn/Ti was 0.1) exhibited a 100% NOx conversion activity in a wide temperature window from 180 to 390 degrees C and a 100% N-2 selectivity from 120 to 390 degrees C under a high space velocity of 36,000 h(-1). Furthermore, MnTiEu-0.3 catalyst presented stronger resistance to concurrent H2O and SO2 poison in comparison with MnOx-TiO2 catalyst without Eu addition. In-situ DRIFT spectra suggested that NH3 can be adsorbed on both Lewis and Bronsted acid sites. For MnOx-TiO2 catalyst, both coordinated NH3 species on Lewis acid sites and NH4+ species on Bronsted acid sites can react with gas-phase NO following E-R mechanism. As regards MnTiEu-03, the NH3-SCR of NO follows both Eley-Rideal and Langmuir-Hinshelwood mechanisms, in which the Eley-Rideal mechanism is predominated. (C) 2017 Elsevier B.V. All rights reserved.