IRON-OXIDE AND CHROMIA SUPPORTED ON TITANIA-PILLARED CLAY FOR SELECTIVE CATALYTIC REDUCTION OF NITRIC-OXIDE WITH AMMONIA

TiO2-pillared clay (PILC) with high surface area, large pore volume, a nd large interlayer spacing was used as the support for mixed Fe2O3 an d Cr2O3 as the catalyst for selective catalytic reduction (SCR) of NO with NH3. The Fe/Cr ratio was varied at a fixed total amount of oxide dopant of 10% (wt). The Fe-Cr/TiO2-PILC with Fe/Cr = 3 showed the high est activity. Compared with commercial V2O5/TiO2 catalysts, the activi ty (on a per gram basis) of the doped pillared clay was approximately twice as high under H2O- and SO2-free conditions and was approximately 40% higher under conditions with H2O and SO2. In addition, its activi ty for SO2 oxidation was only 20%-25% of that of the V2O5-based cataly sts, TPD of NH3 on the Fe-Cr/TiO2-PILC catalyst showed that both M=O a nd M-OH (M=Fe or Cr) were necessary for the SCR reaction, In situ IR s pectra of NH3 showed that there was a higher Bronsted acidity than the Lewis acidity on the surface under reaction conditions and that there existed a direct correlation between the SCR activity and the Bronste d acidity among pillared clays with different Fe/Cr ratios. These resu lts, along with the transient response to O-2, indicated that a simila r mechanism to that on the V2O5 catalyst was operative. The TiO2-pilla red clay used as the support also contributed to the high activity of the Fe-Cr catalyst. The TiO2 pillars combined with the tetrahedral SiO 2 surfaces of the clay apparently gave rise to a high dispersion of Fe 2O3. (C) 1996 Academic Press, Inc.