Manganese supported catalysts for selective catalytic reduction of nitrogen oxides with ammonia Part 1 Characterization

Abstract

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, unoxidized and oxidatively pretreated carbons were used. The introduction of active material was accomplished by an adsorption method using solutions of KMnO₄, KMnO₄+H₂SO₄ or Mn(NO₃)₂. The oxidation state of the active phase and its distribution depended on the precursor and the amount/type of oxygen surface functionalities of their support. KMnO₄ solutions led to the precipitation of Mn₂O₃/MnO₂ crystallites, mostly on the outer surface of active carbon particles. Mn(NO₃)₂ solutions, when introduced onto unpretreated support, resulted in Mn₃O₄/MnO₂ as large aggregates. When H₂SO₄ was added to KMnO₄ solution, small clusters with a broad distribution of sizes were deposited. A monolayer coverage of manganese species could only be obtained when active carbon was pretreated in an oxidizing environment strong enough to produce a considerable amount of carboxylic functionalities. Additionally, the preparation procedures influenced the textural properties.