MANGANESE SUPPORTED CATALYSTS FOR SELECTIVE CATALYTIC REDUCTION OF NITROGEN-OXIDES WITH AMMONIA - PART 1 - CHARACTERIZATION

The preparation of active carbons promoted with manganese was studied with low temperature argon sorption techniques temperature-programmed desorption and X-ray photoelectron spectroscopy. As supports, unoxidiz ed and oxidatively pretreated carbons were used. The introduction of a ctive material was accomplished by an adsorption method using solution s of KMnO4, KMnO4 + H2SO4 or Mn(NO3)(2). The oxidation state of the ac tive phase and its distribution depended on the precursor and the amou nt/type of oxygen surface functionalities of their support. KMnO4 solu tions led to the precipitation of Mn2O3/MnO2 crystallites, mostly on t he outer surface of active carbon particles. Mn(NO3)(2) solutions, whe n introduced onto unpretreated support, resulted in Mn3O4/MnO2 as larg e aggregates. When H2SO4 was added to KMnO4 solution, small clusters w ith a broad distribution of sizes were deposited. A monolayer coverage of manganese species could only be obtained when active carbon was pr etreated in an oxidizing environment strong enough to produce a consid erable amount of carboxylic functionalities. Additionally, the prepara tion procedures influenced the textural properties.