Effect of Hydrothermal Aging Treatment on Decomposition of NO by Cu-ZSM-5 and Modified Mechanism of Doping Ce against This Influence

Abstract

Cu-ZSM-5 and Ce-doped Cu-Ce-ZSM-5 samples were prepared by liquid-phase ion exchange method. The two catalysts were subjected to hydrothermal aging treatment in the simulated flue gas of a coal-fired power station at an ageing temperature of 650–850 °C. The denitration experiment found that the activity of the aged Cu-ZSM-5 was 19.6% to 41% lower than that of the fresh Cu-ZSM-5 at the optimal decomposition temperature of NO at 550 °C, while the aged Cu-Ce-ZSM-5 had only a 14.8% to 31.5% reduction in activity than the fresh Cu-Ce-ZSM-5. The samples were characterized by XRD, BET, H2-TPR, XPS, NO-TPD, etc. The results showed that hydrothermal aging treatment leads to the dealumination of the ZSM-5 framework and reduces the specific surface area and pore volume of the micropore in the sample. It also exacerbates the isolated Cu2+, and the active center {Cu2+-O2−-Cu2+}2+ dimers migrate towards the sample surface and form inactive CuO. Doping with Ce can promote the dispersion of Cu(OH)+, which was the precursor of {Cu2+-O2−-Cu2+}2+. Ce3+ can preferentially occupy the less active bridged hydroxyl exchange sites, so that copper ions occupy the more active aluminum hydroxyl sites, thereby inhibiting the migration of active centers.

Ferrierite and Its Delaminated and Silica-Intercalated Forms Modified with Copper as Effective Catalysts for NH3-SCR Process

“…It is possible that part of the highly dispersed copper species was thermally reduced from Cu 2+ to Cu + during the treatment of the samples in a flow of pure argon at 500 • C, prior to the H 2 -TPR runs. A similar effect was reported and analyzed for the Cu-ZSM-5 samples by Yang et al [38]. This effect may indicate a very high lability in Cu 2+ → Cu + reduction.…”

Ferrierite and Its Delaminated Forms Modified with Copper as Effective Catalysts for NH3-SCO Process

“…This surprising effect is possibly related to the presence of monomeric Cu + cations in the Cu/Al-ITQ-6 sample in the beginning of the H 2 -TPR run. Such thermal reduction of Cu 2+ to Cu + that occurred during the sample outgassing has been reported in scientific literature [28]. The thermal reduction in a flow of helium, used in the samples outgassing step, shows high lability in the reduction of monomeric Cu 2+ cations to Cu + in the Cu/Al-ITQ-6 sample.…”

“…In the spectra of Cu/Al-ITQ-6 and Cu/Ti-ITQ-6 ( Figure 4c), the bands at about 235 nm, characteristic of monomeric coper cations, dominate. The presence of such highly dispersed copper cations is proved by the broad bands above 550 nm, indicating d-d transition in surface Cu 2+ cations in pseudo-octahedral coordination interacting with water molecules [28,29]. The shoulder at about 310 nm, more intensive for Cu/Ti-ITQ-6, is assigned to oligomeric copper oxides species [28,29].…”

“…The presence of such highly dispersed copper cations is proved by the broad bands above 550 nm, indicating d-d transition in surface Cu 2+ cations in pseudo-octahedral coordination interacting with water molecules [28,29]. The shoulder at about 310 nm, more intensive for Cu/Ti-ITQ-6, is assigned to oligomeric copper oxides species [28,29]. Such significant differences in various copper species deposited into the zeolite samples are possibly determined mainly by their porous structure and interaction with the zeolite framework.…”

Titanium–silicon ferrierites and their delaminated forms modified with copper as effective catalysts for low-temperature NH3-SCR

“… 15 The presence of such monomeric copper cations in these samples is also proved by the broad bands above 550 nm, indicating d–d transition phenomena occurred in surface Cu 2+ cations in pseudo-octahedral coordination interacting with water molecules. 31,32 The band at about 305–330 nm is assigned to the presence of oligomeric copper species, while the small shoulder above 400 nm is possibly related to small contribution of copper oxide crystallites. 17,18 It should be noted that intensity of the band characteristic of monomeric copper cations (about 250 nm) is significantly less intense for the Cu-Ti-ITQ-6-25 sample than for Cu-Ti-ITQ-6-50 and Cu-Ti-ITQ-6-100 indicating that there is a lower contribution of such dispersed copper species in the former sample in comparison to later ones.…”