Different lead species deactivation on Mn-Ce activated carbon supported catalyst for low-temperature SCR of NO with NH: Comparison of PbCl, Pb (NO) and PbSO.

Due to the accumulation of heavy metal compounds produced by the sintering process in steel industry, the catalysts used for low-temperature selective catalytic reduction of NO with NH (NH-SCR) might be seriously deactivated. In this work, the deactivation effect of PbCl, Pb(NO), and PbSO on Mn-Ce activated carbon supported catalyst for low-temperature NH-SCR of NO was investigated and compared. Poisoned catalysts were provided by impregnating fresh catalysts with Pb(NO), PbSO and PbCl aqueous solutions, respectively. Deactivation could be observed on the poisoned samples, and the deactivation degree was following PbCl > PbSO > Pb(NO). The catalytic activities of all samples were tested, and the physicochemical properties of fresh and poisoned catalysts were assessed. PbCl caused the most severe deactivation of the catalyst, owing to its poor redox property and surface acidity. Cl could also react with Mn active sites to form -O-Mn-Cl bonds, resulting in additional acid sites, although these newly generated sites were not reactive in NH-SCR reaction process. PbSO exhibited moderate poisoning effect due to the addition of SO, which created new Brønsted acid sites, facilitating the NH adsorption and NO reduction. Pb(NO) had the least poisoning impact on the catalyst due to the NO, promoting the NH activation. The in situ DRIFTS results revealed that NH-SCR reaction over all samples was governed by Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanism, and did not change due to the lead poisoning. Finally, a possible mechanistic model for different lead salts poisoning over Mn-Ce/AC catalyst was proposed.