Regeneration of commercial selective catalyst reduction catalysts deactivated by Pb and other inorganic elements

The regeneration of commercial SCR (Selective Catalyst Reduction) catalysts deactivated by Pb and other elements was studied. The deactivated catalyst samples were prepared by chemical impregnation with mixed solution containing K₂SO₄, Na₂SO₄, CaSO₄, Pb(NO₃)₂ and NH₄H₂PO₄. A novel method combining Ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and H₂SO₄ solution (viz. catalysts treated by dilute EDTA-2Na and H₂SO₄ solution in sequence) was used to recover the activity of deactivated samples, and the effect was compared with single H₂SO₄, oxalic acid, acetic acid, EDTA or HNO₃ solutions. The surface structure, acidity and reducibility of samples were characterized by N₂ adsorption–desorption, inductively coupled plasma optical emission spectrometer (ICP-OES), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), H₂-temperature programmed section (H₂-TPR), NH₃-temperature programmed desorption (NH₃-TPD) and in situ DRIFTS. Impurities caused a decrease of specific surface area and surface reducibility, as well as Brønsted acid sites, and therefore led to severe deactivation of the SCR catalyst. The use of an acid solution alone possibly eliminated the impurities on the deactivated catalyst to some extent, and also increased the specific surface area and Brønsted acid sites and promoted the surface reducibility, thus recovered the activity partially. The combination of EDTA-2Na and H₂SO₄ could remove most of the impurities and improve the activity significantly. The removal of Pb should be an important factor for regeneration. Due to a high removal rate for Pb and other impurities, the combination of EDTA-2Na and H₂SO₄ solutions provided the best efficiency.