MnO2-supported catalytic bodies for selective reduction of NO with NH3: Influence of NO2 and H2O

Abstract

[EN] Catalytic bodies based on MnO, TiO and sepiolite showed an improved behavior for selective reduction of NO with NH at low temperatures. In this work, the influence of Mn %wt and NO and/or water vapor presence was assessed. The materials were prepared by wet equilibrium impregnation of the pre-shaped support. All the catalysts exhibited the characteristic diffraction peaks of TiO-anatase, hexagonal MnOand anhydrous sepiolite. According to SEM-EDX, MnO was preferentially deposited over TiO The optimum nominal content of Mn was 7.5 %wt, what may be related to an appropriate particle dispersion that confers the suitable properties: lower acid strength, and better redox properties with improved reducibility. This catalyst was then evaluated under NO and/or HO presence. NO improved the catalytic response and the best result was obtained with 1:1 NO:NO ratio showing 90 % NO conversion and 97 % N selectivity at very low temperature, 110 °C. A higher amount of NHNO seems to be formed with the increase in the NO/NO ratio causing a modification of N selectivity. Although water presence affected the performance, mainly at low temperatures, the catalyst showed good resistance to water vapor at temperatures above 180 °C maintaining good activity (90 % of NO conversion and 96 % of N selectivity). When NO was co-added to the feed, a beneficial effect was again observed with 91 % of NO and 95 % of N selectivity converted at 143 °C. At low temperatures, deactivation has to do with a competitive effect of HO with NO towards the adsorption centers, which decreases the concentration of nitrate species adsorbed on the surface. However, the adsorption of ammonia was less affected. 7.5 Mn catalyst is a highly efficient system to work in real conditions, where there is water in gas stream. In this situation, co-feeding NO improves activity.