Modified activated carbons for the selective catalytic reduction of NO with NH3

Abstract

Activated carbons, modified with nitrogen- and oxygen-containing organic compounds by wet impregnation, followed by pyrolysis and CO 2 activation, have been used for the low temperature selective catalytic reduction (SCR) of NO with NH 3 (385–550 K). Of all the additives studied, only glucosamine results in an outstanding increase of the activity, which might be ascribed to the creation of stable surface oxygen complexes. These complexes can only be removed at relatively high temperatures and probably affect the carbon surface in such a way that adsorption of the reactants is improved, resulting in higher NO conversions compared to the original carbon. The explicit role of the incorporated nitrogen is not unequivocally clear. Apparently, the overall SCR activity is the result of a combination of the following factors: interaction of oxygen with the carbon, the presence of stable oxygen groups, the nitrogen content and the accessibility of the pores. For the modified carbons the SCR reaction is zeroth order in NH 3 and first order in NO. Furthermore, the oxygen dependency can be modelled by a Langmuir type of adsorption. Over the unmodified carbons a second type of selective NO reduction can be distinguished in which the carbon only acts as an adsorbents and for which a negative apparent activation energy is observed.