CHARACTERIZATION AND REACTIVITY OF TIO2-SUPPORTED MOO3 DE-NO-X SCR CATALYSTS

TiO2-supported MoO3 catalysts, with MoO3 loading similar to that of co mmercial DeNO(x)-SCR catalysts (in the range 0-11% w/w) have been prep ared, characterized and tested in the NO reduction by NH3. The structu ral and morphological characteristics of the anatase-TiO2 support are not significantly changed upon MoO3 addition. For MoO3 loading below o r near 9% (w/w) (corresponding to the formation of the theoretical mon olayer), evidence for the presence of isolated molybdenyl surface spec ies have been collected by FT-IR, Laser Raman and EPR spectroscopies. Above this loading, the presence of crystalline MoO3 is observed. The MoO3/TiO2 catalysts are active in the reduction of NO by NH3: the reac tivity of the catalysts increases on increasing the MoO3 loading, wher eas the N-2 selectivity decreases due to the formation of undesired N2 O. The formation of N2O is primarily ascribed to a reaction between NH 3 and NO, and not to the ammonia oxidation reaction. A comparison with a WO3/TiO2 catalyst having similar molar composition indicates that t he WO3- and MoO3-containing samples exhibit similar structural and mor phological characteristics, but different reactivity: the WO3/TiO2 sam ple is less active but more selective in the SCR reaction. On the basi s of EPR data, the different catalytic behavior has been tentatively a scribed to the different redox characteristics of the samples. (C) 199 8 Elsevier Science B.V. All rights reserved.