Low-temperature SCR of NOx with NH3 over Nomex (TM) rejects-based activated carbon fibre composite-supported manganese oxides Part II. Effect of procedures for impregnation and active phase formation

The first part of this work dealt with the preparation and conditioning of Nomex (TM) rejects-based activated carbon fibre (ACF) composites to be used as catalytic supports of manganese oxides for the low-temperature selectiv e catalytic reduction of nitric oxide with ammonia. In this second part, th e catalytic results obtained by applying different impregnation procedures, including the previous exchange of the oxidised support with solutions of NaOH, are described. Washing the support with deionised water after both th e Na-exchange and the impregnation steps improved the activity of the resul ting catalyst. For the active phase formation (manganese oxide) on the supp ort surface, different treatments were tested. It was determined that a tre atment of the impregnated catalyst consisting of a stage of NO/O-2/NH3 adso rption/reaction at 150 degreesC followed by heat treatment up to 400 degree sC under inert atmosphere, and a final stage of mild oxidation at 200 degre esC yielded the best catalytic results The final oxidation state of mangane se was estimated to be between II and III. This final fabrication procedure yielded catalysts that in conditions of hi gh spatial velocities (11000-25 000 h(-1)) and negligible pressure drop. sh owed a high catalytic activity at 150 degreesC, with NOx reduction percenta ges close to 85%, selectivities above 95% and low gasification rates of the carbonaceous support. (C) 2001 Elsevier Science B.V All rights reserved.