Intrinsic mechanism insight of the interaction between lead species and the Vanadium-based catalysts based on First-principles investigation.

Abstract Lead (Pb) species trigger serious poisoning of selective catalytic reduction (SCR) catalysts. To improve the Pb resistance ability, revealing the impact mechanism of Pb species on the commercial SCR catalysts from a molecular level is of great significance. Herein, first-principles calculations were applied to unveil the Pb adsorption mechanism on the vanadium-based catalysts, the results were also compared with the previous experimental findings. The intrinsic interaction mechanism between Pb and catalyst components was interpreted by clarifying the change of the catalyst electronic structures (including charge transfer, bond formation situations, and active sites reactivities). It is found that the adsorption of Pb species belongs to chemisorption, evident electron transfer with the catalyst surface is inspected and intense charge transfer indicates strong adsorption. A remarkable interaction with the V = O active sites occurs and stable Pb-O bonds are formed, which significantly changes the electronic structures of the V = O sites and inhibits the NH3 adsorption, thus suppressing the SCR activity. Finally, thermodynamic analysis was applied to elucidate the temperature influence on Pb adsorption. It is found that Pb adsorption on catalysts cannot proceed spontaneously over 500 K. At higher temperatures the adsorption is inhibited and the Pb species become less stable, which partially explains why the Pb-poisoning effect at high temperatures is relatively moderate than that at low temperatures.