New Insight into the Doping Effect of Transition Metals (Fe, Ti, Mn, and Ce) on the Structure and Catalytic Performance of Cu-SSZ-13 Zeolite Catalysts for the NH3-SCR Reaction

Cu-SSZ-13 zeolite catalysts were synthesized via one-pot strategies and further doped with different transition metals (TM = Fe, Ti, Ce, Mn) by ion exchange methods. The synthesized catalysts were assessed by tests of NH3-SCR activity, hydrothermal stability, and antisulfur-poisoning ability along with various characterizations including XRD, XPS, and H2-TPR. Results indicate that different dopants significantly affect the catalytic performance. The Fe doped Fe0.86/Cu2.14-SSZ-13 catalyst exhibited an expanded operation temperature window, outstanding high-temperature SCR activity, and increased durability against hydrothermal aging as well as SO2 poisoning, while other dopants such as Mn or Ce seem quite unsatisfactory. Isolated Cu2+ and monomeric Fe3+ are revealed as the major active species contributing to low-temperature NH3-SCR activity and efficient high-temperature NO conversion, respectively. TM doping led to substitution of the Cu1 species (isolated Cu2+ near the octatomic ring window) at ion-exchange sites, zeolite framework structure collapse, and migration of active Cu species into more stable sites during hydrothermal aging, as well as agglomeration of Cu/Fe species during SO2 pretreatment. Thus, the TM/Cu-SSZ-13 catalysts presented obvious catalytic activity deterioration after hydrothermal aging or sulfur poisoning.