Promotion effect of cerium doping on iron-titanium composite oxide catalyst for selective catalytic reduction of NOx with NH3
A series of cerium-doped iron-titanium composite oxide catalysts (FeCeaTi, a = 0.1-1.0) prepared by the urea homogeneous precipitation method were investigated for selective catalytic reduction of NOx with NH3 (NH3-SCR). Over all FeCeaTi samples, a promotion effect for NOx reduction was induced by the introduction of cerium, with the FeCe0.3Ti catalyst exhibiting the best catalytic performance, even under a high GHSV of 250,000 h-1. As indicated by kinetic studies, interestingly, the FeCe0.3Ti catalyst exhibited a higher activation energy for NH3-SCR process, while possessed a pre-exponential factor with three orders of magnitude higher than FeTi. Going deeper, extensive characterization including N2-physisorption, XRD, Raman, NH3/NOx-TPD, XPS, EPR, and H2-TPR was carried out. XRD and Raman results showed that introduction of suitable amounts of Ce into FeTi samples promoted the dispersion of Fe and Ti. Such higher dispersion of these two components increased the capacities for NOx adsorption and activation and weakly bonded ammonia over FeCe0.3Ti, thus promoting the occurrence of the L-H pathway of NH3-SCR at low temperatures. H2-TPR result indicated that the reduction of FeCe0.3Ti occurred at a higher temperature than that of FeTi, which may be a reason for its higher activiation energy for NH3-SCR. More importantly, H2-TPR measurement revealed that more redox sites were made available for NOx reduction over FeCe0.3Ti than FeTi, leading to higher intrinsic activity for the former sample.