Low-temperature SCR of NOx with NH3 over Nomex™ 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 selective catalytic reduction of nitric oxide with ammonia. In this second part, the 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 the Na-exchange and the impregnation steps improved the activity of the resulting catalyst. For the active phase formation (manganese oxide) on the support surface, different treatments were tested. It was determined that a treatment of the impregnated catalyst consisting of a stage of NO/O-2/NH3 adsorption/reaction at 150 degreesC followed by heat treatment up to 400 degreesC under inert atmosphere, and a final stage of mild oxidation at 200 degreesC yielded the best catalytic results The final oxidation state of manganese was estimated to be between II and III. This final fabrication procedure yielded catalysts that in conditions of high spatial velocities (11000-25 000 h(-1)) and negligible pressure drop. showed a high catalytic activity at 150 degreesC, with NOx reduction percentages close to 85%, selectivities above 95% and low gasification rates of the carbonaceous support. (C) 2001 Elsevier Science B.V All rights reserved.