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, and large interlayer spacing was used as the support for mixed Fe2O3 and 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 highest activity. Compared with commercial V2O5/TiO2 catalysts, the activity (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 activity for SO2 oxidation was only 20%-25% of that of the V2O5-based catalysts, TPD of NH3 on the Fe-Cr/TiO2-PILC catalyst showed that both M=O and M-OH (M=Fe or Cr) were necessary for the SCR reaction, In situ IR spectra 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 Bronsted acidity among pillared clays with different Fe/Cr ratios. These results, along with the transient response to O-2, indicated that a similar mechanism to that on the V2O5 catalyst was operative. The TiO2-pillared clay used as the support also contributed to the high activity of the Fe-Cr catalyst. The TiO2 pillars combined with the tetrahedral SiO2 surfaces of the clay apparently gave rise to a high dispersion of Fe2O3. (C) 1996 Academic Press, Inc.