Promotion of transition metal oxides on the NH_3-SCR performance of ZrO_2-CeO_2 catalyst

Chromium oxide and manganese oxide promoted ZrO_2-CeO_2 catalysts were prepared by a homogeneous precipitation method for the selective catalytic reduction of NO_x with NH_3. A series of characterization including X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM),Brunauer-Emmett-Teller (BET) surface area analysis,H_2 temperature-programmed reduction (H_2-TPR),and X-ray photoelectron spectroscopy (XPS) were used to evaluate the influence of the physicochemical properties on NH_3-SCR activity. Cr-Zr-Ce and Mn-Zr-Ce catalysts are much more active than ZrO_2-CeO_2 binary oxide for the low temperature NH_3-SCR, mainly because of the high specific surface area, more surface oxygen species,improved reducibility derived from synergistic effect among different elements. Mn-Zr-Ce catalyst exhibited high tolerance to SO_2 and H_2O. Cr-Zr-Ce mixed oxide exhibited >80% NO_x conversion at a wide temperature window of 100°C-300°C. In situ DRIFT studies showed that the addition of Cr is beneficial to the formation of Bronsted acid sites and prevents the formation of stable nitrate species because of the presence of Cr~(6+). The present mixed oxide can be a candidate for the low temperature abatement of NO_x