Promotion effect of cerium doping on iron–titanium composite oxide catalysts for selective catalytic reduction of NOx with NH3

Abstract

A series of cerium-doped iron–titanium composite oxide catalysts (FeCe_aTi, a = 0.1–1.0) prepared by a urea homogeneous precipitation method were investigated for selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). Over all the FeCe_aTi samples, a promotion effect for NO_x reduction was induced by the introduction of cerium, with the FeCe_0.3Ti catalyst exhibiting the best catalytic performance, even at a high GHSV of 250 000 h⁻¹. As indicated by kinetic studies, interestingly, the FeCe_0.3Ti catalyst exhibited a higher activation energy for the NH₃-SCR process while possessing a pre-exponential factor three orders of magnitude higher than that of FeTi. Going deeper, extensive characterization including N₂-physisorption, XRD, Raman, NH₃/NO_x-TPD, XPS, EPR, and H₂-TPR was carried out. XRD and Raman results showed that the introduction of suitable amounts of Ce into the FeTi samples promoted the dispersion of Fe and Ti. Such higher dispersion of these two components increased the capacities for NO_x adsorption and activation and weakly bonded ammonia over FeCe_0.3Ti, thus promoting the occurrence of the L–H pathway of NH₃-SCR at low temperatures. H₂-TPR results indicated that the reduction of FeCe_0.3Ti occurred at a higher temperature than that of FeTi, which may be a reason for its higher activation energy for NH₃-SCR.