Abstract
•The poisoning effects of PbO-doped Mn-Ce/TiO2 catalysts for low temperature NH3-SCR were investigated.•Low concentration of Mn4+ and chemisorbed oxygen (Ob) were not favorable for the generation of intermediates.•The decreased Ce3+ and less reducible of manganese oxides hindered the redox cycle (Mn3++Ce4+↔Mn4++Ce3+).•The doping of PbO not only altered acid sites but also inhibited ammonia adsorption as well as activation.•The poisoning of PbO resulted in the decrease of ad-NOx species (only a spot of bidentate nitrates remained).
Lead oxide (PbO) as one of the typical heavy metals in flue gas from power plants has strong accumulation as well as poisoning effects on SCR catalysts. In this paper, a series of PbO-doped Mn-Ce/TiO2 catalysts were synthesized by impregnation method. The poisoning effects of PbO over Mn-Ce/TiO2 samples for selective catalytic reduction of NO by NH3 were investigated based on catalytic activity test and characterizations. The NO conversion of Mn-Ce/TiO2 was greatly decreased after the addition of PbO. It was obvious that the NO conversion efficiency of Mn-Ce/TiO2 catalyst declined from 96.75% to about 40% at 200°C when Pb:Mn molar ratio reached 0.5. Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Hydrogen temperature programmed reduction (H2-TPR), Ammonia temperature programmed desorption (NH3-TPD) and Fourier transform infrared spectroscopy (FT-IR) were carried out to study the deactivation reasons of PbO poisoned catalysts. Manganese oxides’ crystallization, less reducible of manganese and cerium oxides, the decreasing of surface area, Mn4+ as well as Ce3+ concentration and chemisorbed oxygen (Ob) after the introduction of PbO, all of these resulted in a poor SCR performance. Furthermore, the alteration of acid sites (especially Brönsted acid sites), low ammonia adsorbance, an obvious reducing of ad-NOx species (only a spot of bidentate nitrates remained) and the vanishing of amide species contributed to the deactivation of Mn-Ce/TiO2 catalyst by PbO doping as well.