The deactivation mechanism of Pb on the Ce/TiO2 catalyst for the selective catalytic reduction of NOx with NH3: TPD and DRIFT studies

Abstract

It was well recognized that Pb had a poisoning effect on a SCR catalyst. In this study, the deactivation mechanism of Pb on the Ce/TiO₂ catalyst was investigated based on the characterization results of TPD and in situ DRIFT studies. It was found that the addition of Pb on the Ce/TiO₂ catalyst not only inhibited the adsorption and activation of NH₃ species, but also led to the decrease of the activity of adsorbed NH₃ species in the SCR reaction. The adsorption of NOx species and the oxidation of NO by O₂ over the Ce/TiO₂ catalyst were also suppressed by the addition of Pb, while the reactivity of adsorbed NO₂ species did not decrease. Moreover, the results revealed that the NH₃-SCR reaction over the Ce/TiO₂ catalyst followed both the E–R and L–H mechanisms, while the NH₃-SCR reaction over Ce/TiO₂-Pb was mainly controlled by the L–H mechanism. The contributions of the L–H mechanism to the SCR reactions over Ce/TiO₂ and Ce/TiO₂-Pb decreased with increasing reaction temperature. The deactivation of Ce/TiO₂-Pb was mainly attributed to the suppressed NH₃ adsorption and activation, accompanied by the inhibited NO oxidation and the decrease of Brønsted acid sites.