Catalytically modified fly-ash filters for NOx reduction with NH3

Catalytic filters for simultaneous removal of fly-ashes and nitrogen oxides have been prepared by deposition of a V2O5·Al2O3 catalyst into the pores of commercially available α-Al2O3 tubular filters by means of two different techniques (i.e. sol-gel; nitrate-urea). The vanadia content of the catalyst was optimised so as to achieve the highest catalytic activity towards NO selective catalytic reduction (SCR) with ammonia. The kinetics of the SCR reaction and of ammonia oxidation (the major parasite reaction, leading mostly to N2O formation) on the above catalysts have been assessed as well in a differential fixed-bed reactor. The effect of the catalyst load of the prepared filters has been assessed, showing that optimum conditions can be found in which considerable abatement of nitrogen oxides can be achieved for feed superficial velocities of industrial interest (up to 65 m h−1). A significant increase on the attainable NO conversion (from 86 to 96% for the best catalytic filter prepared) was furthermore obtained when operating at higher-than-ambient pressures, which also turned into an increase of reaction selectivity and lower NH3 slippage through the filter.