Poisoning Effects of Alkali and Alkaline Earth Metal Doping on Selective Catalytic Reduction of NO with NH3 over the Nb-Ce/Zr-PILC Catalysts

Abstract

The poisoning effects of alkali metals (K and Na) and alkaline earth metals (Ca and Mg) on catalytic performance of the 2Nb4Ce/Zr-PILC catalyst for the selective catalytic reduction of NOx with NH3 (NH3-SCR) were investigated, and physicochemical properties of the catalysts were characterized by means of the X-ray diffraction XRD (XRD), Brunner−Emmet−Teller (BET), hydrogen temperature-programmed reduction (H2-TPR), X-ray Photoelectron Spectroscopy (XPS), ammonia temperature-programmed desorption (NH3-TPD), and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) techniques. Doping of M (M = K, Na, Ca, and Mg) deactivated the 2Nb4Ce/Zr-PILC catalyst according to the sequence of 0.8 K > 0.8 Na > 0.8 Ca > 0.8 Mg (M/Ce molar ratio = 0.8). The characterization results showed that the decreases in redox ability, NH3 adsorption, Ce3+/Ce4+ atomic ratio, and amount of the chemisorbed oxygen (Oβ) were the important factors influencing catalytic activities of the alkali metal-and alkaline earth metal-doped samples. Consequently, compared with the Mg- and Ca-doped samples, doping of K caused the 2Nb4Ce/Zr-PILC sample to possess the lowest redox ability, NH3 adsorption, and amount of the Oβ species, which resulted in an obvious deactivation effect.

A highly active Ca/Cu/YCeO2–TiO2 catalyst for the transient reduction of NO with CO and naphthalene under oxidizing conditions

“…The weak blocking effect of the large pores seems to be related to the high dispersion of copper, 28 whereas the alkaline metal effectively blocked large pores. 29 Note that the peak at 170 Å was preserved for the Ca/Cu/YCeO 2 –TiO 2 catalyst despite the decrease in the entire pore distribution. Recall that the Ca/Cu/YCeO 2 –TiO 2 catalyst was first impregnated with Cu and then further impregnated with Ca after calcining.…”

The Deactivation Mechanism of the Mo-Ce/Zr-PILC Catalyst Induced by Pb for the Selective Catalytic Reduction of NO with NH3

“…N 2 adsorption–desorption isotherms of the 3Mo4Ce/Zr-PILC and Pb-poisoned 3Mo4Ce/Zr-PILC catalysts are shown in Figure 3 . It can be seen that the isotherms of the catalysts were obviously in accordance with type I in the low relative pressure range, according to the IUPAC classification, which conformed to the characteristics of microporous materials [ 16 ]. The adsorbed volumes of the catalysts increased significantly in the p / p 0 (<0.01) range, which was due to the formation of a large number of micropores during the pillaring process.…”