The poisoning effect of single elements on commercial V₂O₅-WO₃/TiO₂ catalysts has been studied in the past decades. In this study, the combined effects of two multi-element systems (phosphorus-potassium and phosphorus-lead) on V₂O₅-WO₃/TiO₂ catalysts were studied by diverse characterizations. The results show that potassium and lead can result in the deactivation of catalysts to different degrees by reacting with active acid sites and reducing the amount of V⁵⁺. However, phosphorus displays slight negative influence on the NO_x conversion of the catalyst due to the comprehensive effect of reducing V⁵⁺ amount and generating new acid sites. The samples poisoned by phosphorus–potassium and phosphorus–lead have higher NO_x conversion than that by potassium or lead, because doped potassium or lead atoms may react with new acid sites generated by phosphate, which liberates more V–OH on the surface of catalysts and reduces the poisoning effects of potassium or lead on vanadium species and active oxygen species.

The accumulation of NH₄HSO₄ leads to the deactivation of commercial V₂O₅-WO₃/TiO₂ catalyst (VWTi) in practical application. The commercial catalyst is modified with 0.3 wt. % Ce and 0.05 wt. % Cu (donated as VWCeCuTi), and its sulfur resistance is noticeably improved. After loading 20 wt. % NH₄HSO₄, the NO_x conversion of VWCeCuTi-S remains 40% at 250 °C, higher than that of VWTi-S (25%). Through a series of characterization analyses, it was found that the damaged surface areas and acid sites are the key factors for the deactivation of S-poisoned samples. However, surface-active oxygen and NO adsorption are increased by NH₄HSO₄ deposition, and the L–H mechanism is promoted over S-poisoned samples. Due to the interaction between V, Ce and Cu, the surface-active oxygen over VWCeCuTi-S is increased, and then NO adsorption is promoted. In addition, VWCeCuTi-S obtains a higher V⁵⁺ ratio and a better redox property than VWTi-S, which in turn accelerates the NH₃-SCR reaction. More NO adsorption and encouraged reaction contribute to the better sulfur resistance of VWCeCuTi.

Direct leaching with NaOH can be an economically acceptable method for vanadium (V) and tungsten (W) recovery from spent selective catalytic reduction (SCR) catalysts. However, different chemical-physical characteristics of catalysts would affect the V and W leaching. In this paper, the V and W leaching behavior of various sources of SCR catalysts with a local difference (yellow and gray color) were systematically investigated with alkali leaching solution under ambient pressure. Different leaching efficiencies from yellow and gray color areas were correlated with oxidation states and species of V and W on catalyst surfaces, as characterized by X-ray photoelectron spectroscopy (XPS), Raman, Fourier transform infrared spectroscopy (FTIR), and other analytic methods. For the V leaching efficiency, the samples from a gray area of catalysts (40.0–51.0%) were lower than that from the yellow area (66.8–69.8%). The higher molar ratio of V³⁺ and a lower molar ratio of V⁵⁺, and the lower total V content on the surface of the samples from the gray area could be the main reasons for the lower V leaching efficiency. As for the W leaching efficiency, the samples from the gray area (44.6–57.3%) were slightly higher than that from the yellow area (38.0–52.6%) of catalysts. The less total W content of surface species and stronger interaction among V–W–Ti of yellow area samples resulted in the lower leaching efficiency. These differential leaching efficiencies needed to be taken into consideration for recovering V and W from spent SCR catalysts.