Nanostructured MnOx catalysts for low-temperature NOx SCR

• Manganese oxides-based catalysts were synthesized for low temperature NOx SCR.
• Different structures, morphologies and surface areas were obtained.
• All samples showed similar reduction behaviour, corresponding to two different paths.
• Catalytic activity tests showed that the presence of Mn3O4 seems a relevant factor.
• SCR activity is affected by Mn oxidation state, surface area and crystallinity.

Manganese oxides with different structures and morphologies have been investigated as catalysts for low temperature SCR by preparing a series of samples by both SCS (Solution Combustion Synthesis) and co-precipitation methods. The samples have been characterized by XRD, BET, H2-TPR, NH3-TPD, FESEM and their catalytic activity tested for NOx removal in the range of temperature of interest (120–350 °C) both in the presence and in the absence of SO2, and after catalyst regeneration from sulphur deactivation. The different preparation procedures allowed to obtain MnOx systems with variable average oxidation state (measured through H2-TPR) that can be put in correlation with the porosity and the morphology measured by the other techniques, and the resulting catalytic performances in the SCR. The presence of Mn3O4 in the resulting material with low degree of crystallinity seemed to be the key factor to get the best catalyst among those prepared, being this phase not only active, but very selective towards the production of N2. Finally, the presence of a relatively high amount of SO2 among reactants (100 ppm) drastically reduces the activity of all samples, but regeneration of catalyst for 2 h at 400 °C almost completely restores the catalytic performances.