Characterization and NH3-SCR reactivity of Cu-Fe-ZSM-5 catalysts prepared by solid state ion exchange: The metal exchange order effect

Direct Synthesis of Hierarchical FeCu‐ZSM‐5 Zeolite with Wide Temperature Window in Selective Catalytic Reduction of NO by NH3

“…Notably, the spectra of Fe/ZSM-5, Cu/ZSM-5, Fe/Cu/ ZSM-5, and FeCu-ZSM-5 are distinctly different, revealing that the Fe and Cu species exist in various forms. [19] In this study, Fe/ZSM-5 and Fe/Cu/ZSM-5 display a band centered at 214 nm which is attributed to tetra-coordinated Fe 3 + ions in the framework of the Fe-substituted zeolites, [20] a band sited at 383 nm ascribes to oligo nuclear Fe x O y clusters, [11,21] and a band located at 520 nm due to d-d transition of α-Fe 2 O 3 which are 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 fairly inactive in NH 3 -SCR reaction. [18] For Fe species, it is well accepted that the band below 300 nm belongs to isolated iron ions in tetrahedral or octahedral coordination, the signal between 300 and 400 nm is assigned to oligomeric Fe oxo entities, and the peak above 400 nm is attributed to iron oxide aggregates.…”

“…[18] For Fe species, it is well accepted that the band below 300 nm belongs to isolated iron ions in tetrahedral or octahedral coordination, the signal between 300 and 400 nm is assigned to oligomeric Fe oxo entities, and the peak above 400 nm is attributed to iron oxide aggregates. [19] In this study, Fe/ZSM-5 and Fe/Cu/ZSM-5 display a band centered at 214 nm which is attributed to tetra-coordinated Fe 3 + ions in the framework of the Fe-substituted zeolites, [20] a band sited at 383 nm ascribes to oligo nuclear Fe x O y clusters, [11,21] and a band located at 520 nm due to d-d transition of α-Fe 2 O 3 which are 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 fairly inactive in NH 3 -SCR reaction. [22] While, the UV-vis DRS spectrum of FeCu-ZSM-5 has a dominant absorbance band at 250 nm due to the oxygen-to-iron charge transfer, indicating the existence of isolated Fe species which are introduced into the zeolite framework in tetrahedral coordination.…”

“…[34] For Fe/Cu/ ZSM-5, the reduction peaks shift to lower temperatures comparing to Fe/ZSM-5, which is caused by the interaction between iron and copper species. [11] Another high temperature peak at around 370°C corresponds to the reduction of Cu + to Cu 0 . With reference to the study of Jouini et al, the peak at about 250°C for FeCu-ZSM-5 is ascribed to the reduction of isolated Cu 2 + ions with tetrahedral coordination to Cu + .…”

“…For example, Panahi et al reported that the bimetallic FeÀ Cu/ZSM-5 nanocatalyst possessed the highest catalytic activity for NO conversion among the different transition metal (Co, Mn, Cr, and Fe) modified Cu/ZSM-5 zeolites. [11] Although the synergistic effect of iron and copper in the bimetallic zeolites on the NH 3 -SCR performance has attracted much attention, its preparation faces several challenges. [10] Besides, Jouini et al investigated the effect of metal exchange order over CuÀ Fe-ZSM-5 and FeÀ Cu-ZSM-5 prepared by solidstate ion exchange.…”

“…They found that the metal exchange order greatly affected the metal speciation and the catalytic behavior of the studied catalyst. [11] Although the synergistic effect of iron and copper in the bimetallic zeolites on the NH 3 -SCR performance has attracted much attention, its preparation faces several challenges. Traditionally, several post-synthesis approaches were used to prepare the iron and/or Cu modified ZSM-5, including wet impregnation and solid-state or liquid-phase ion-exchange.…”