Selective catalytic reduction of nitric oxide by ammonia on pillared clay catalysts: Possible mechanism and promoters

The delaminated Fe2O3-pillared clay shows high activities for selective catalytic reduction (SCR) of NO by NH3. Temperature program desorption (TPD) studies show that large amounts of NOx are adsorbed on the pillared clay catalyst at the SCR reaction temperatures (i.e. near 400 degrees C). This result indicates that a Langmuir-Hinshelwood type mechanism (for reaction between chemisorbed NOx and NHx on the surface to form N-2) is operative for the pillared clay catalyst, which is in contrast to the SCR reaction on the commercial vanadia-based catalysts. The SCR activities for the delaminated Fe2O3-pillared clay catalyst are higher than that of a commercial-type V2O5 + WO3/TiO2 catalyst under SO2 + H2O free conditions, but became lower in the presence of SO2 + H2O. However, when promoted by doping 1-3% Cr2O3, the pillared clay catalyst exhibits higher SCR activities than the commercial-type catalyst in the presence of SO2 + H2O at all practical SCR reaction temperatures.