Rq. Long et Rt. Yang, Selective catalytic reduction of nitrogen oxides by ammonia over Fe3+-exchanged TiO2-pillared clay catalysts, J CATALYSIS, 186(2), 1999, pp. 254-268
Fe-exchanged TiO2-pillared clay (PILC) catalysts were prepared and used for
selective catalytic reduction (SCR) of NO, by ammonia. They were also char
acterized for surface area, pore size distribution, and by XRD, H-2-TPR, an
d FT-IR methods. The Fe-TiO2-PILC catalysts showed high activities in the r
eduction of NOx by NH3 in the presence of excess oxygen. SO2 further increa
sed the catalytic activities at above 350 degrees C, whereas H2O decreased
the activity slightly. The catalysts were about twice as active as commerci
al-type V2O5-WO3/TiO2 catalyst in the presence of H2O and SO2. Moreover, co
mpared to the commercial catalyst, the Fe-TiO2-PILC catalysts had higher N-
2/N2O product selectivities (e.g., 0-1% vs 9% N2O at 400 degrees C) and sub
stantially lower activities (by 74-88%) for SO2 oxidation to SO3 under the
same reaction conditions. The activity was further increased to over three
times that of the vanadia-based catalyst when Ce was added. The high activi
ty and low N2O selectivity for the Fe-TiO2-PILC catalysts were attributed t
o their low activity in the oxidation of ammonia, as compared with vanadia
catalysts. XRD patterns of Fe-TiO2-PILC were similar to those of TiO2-PILC,
showing no peaks due to iron oxide, even when the iron content reached 20.
1%. The TPR results indicated that iron in the Fe-TiO2-PILC catalysts with
lower iron contents existed in the form of isolated Fe3+ ions. The activiti
es of Fe-TiO2-PILC catalysts were consistent with their surface acidities,
which were identified by FT-IR of the NH3-adsorbed samples. The enhancement
of activities by H2O + SO2 was attributed to the increase of surface acidi
ty resulting from the formation of surface sulfate species of iron. (C) 199
9 Academic Press.