Ce–Ti Amorphous Oxides for Selective Catalytic Reduction of NO with NH₃: Confirmation of Ce–O–Ti Active Sites

Abstract

The amorphous Ce-Ti mixed oxides were reported to be catalysts for selective catalytic reduction of NO(x) with NH(3), in which Ce and not Ti acts as their solvent in spite of the fact that Ce is low in content. The amorphous catalysts were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) equipped with selective area electron diffraction (SAED). The Ce-Ti amorphous oxide shows higher activity than its crystalline counterpart at lower temperatures. Moreover, the presence of small CeO(2) crystallites as for the impregnated sample is deleterious to activity. The Ce-O-Ti short-range order species with the interaction between Ce and Ti in atomic scale was confirmed for the first time to be the active site using temperature programmed reduction with H(2) (H(2)-TPR), in situ FTIR spectra of NO adsorption, X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine-structure (XAFS). Lastly, the Ce-O-Ti structure was directly observed by field-emission TEM (FETEM).

The Selective Catalytic Reduction of NOx Over Cd-Ce-Ti Metal Oxide Catalysts

“…As shown in Figure 1, the diffraction peaks at 25.4°, 47.6° are ascribed to the characteristic reflections of anatase TiO 2 and the peak at 28.6° is ascribed to fluorite CeO 2 . There is no peak at 27.5° in the samples, which indicates that there is no rutile titania existing in all samples [17,18]. Moreover, no obvious characteristic peak assigned to a particular phase oxide is observed in 2% and 3% samples, which indicates that the amorphous phase was formed and become dominant phase in the samples [19].…”

Novel Fe‐W‐Ce Mixed Oxide for the Selective Catalytic Reduction of NOx with NH3 at Low Temperatures

“…The XRD patterns of the Fe containing catalysts are compared to the W-Ce catalyst in Figure 2. [21]. Meanwhile, the peaks were not very sharp, which pointed at low crystallinity of the sample [16].…”

“…The XRD patterns of the Fe containing catalysts are compared to the W-Ce catalyst in Figure 2. All peaks of W-Ce catalyst can be assigned to cerianite (CeO 2 3 were also the dominant species [21]. Meanwhile, the peaks were not very sharp, which pointed at low crystallinity of the sample [16].…”

“…A reason may be that WO3 is said to increase the strength and amount of Brönsted acid sites on catalyst surface [20]. Chen et al assume that tungsten promotes the NO to NO2 oxidation, which facilitates the fast SCR reaction that can occur at low temperatures [21]. Furthermore, tungsten seems to have the ability to inhibit the oxidation of NH3 to N2O and therefore increases the N2 selectivity [19].…”

The use of ceria for the selective catalytic reduction of NOx with NH3

“…High surface area and good redox properties are important for catalytic activity, while the strong interaction between Ce and Ti and a high concentration of amorphous, or highly dispersed nanocrystalline, ceria could explain the excellent performance of the catalyst. Using various methods, Li et al [32] confirmed that the active site of a CeO2/TiO2 catalyst was the Ce-O-Ti short-range ordered species with the interaction between Ce and Ti being at the atomic level. To improve the resistance to alkali metal poisoning, a titanate nanotube in which CeO2 was confined was designed and synthesized by Chen et al [33].…”