Redox behavior and mobility of copper ions in NaZSM-5 zeolite during oxidation

Abstract

The redox behavior and mobility of the Cu ions in Cu ion-exchanged NaZSM-5 zeolites (Cu-NaZ) during oxidation of benzyl alcohol were examined by CO adsorption, IR absorption measurement of CO adsorbed on the Cu-NaZ, and diffuse reflectance spectra measurement. The properties and oxidation state of the Cu ions in Cu ion-exchanged S i 0 2 (Cu-SiOz) were also investigated by similar methods, focusing on the comparison with those in the Cu-NaZ zeolites. The Cu-NaZ zeolites with higher degrees of Cu ion exchange were found to have a t least two different kinds of C u ions, in contrast to the Cu-SiOz which showed the presence of only one kind of C u ion. The redox process of benzyl alcohol oxidation catalyzed by Cu-NaZ was followed by the IR measurement using CO as a probe molecule. Benzyl alcohol, ethanol, and isopropyl alcohol were found to cause the Cu ions, which located in recessed sites, to relocate to a more open space such as a channel intersection. The Cu ions were found to be reversibly displaced depending on the presence or absence of the alcohol molecule. In the oxidation process, the adsorbed benzyl alcohol was suggested to have the function of withdrawing Cu ions from recessed sites to sites accessible by the reactant molecule, a t which benzyl alcohol was oxidized to benzaldehyde. The catalytic oxidation activity for benzyl alcohol was found to correlate with the amount of Cu ions which can be geometrically displaced in the Cu-NaZ zeolite.

A Cu/Al-MCM-41 mesoporous molecular sieve: application in the abatement of no in exhaust gases

“…These results are in accordance with those published by Minchev et al (2001), who found that the surface area of |Cu x |[Si y Al]-MCM-41 mesoporous solids is influenced by Cu content and by the method used during Cu impregnation. hexagonally coordinated by water molecules and O atoms found in the framework of the molecular sieves studied (Itho et al, 1994). In accordance with Moretti et al (2001), this band disappears when |Cu x.…”

Cu and Co exchanged ZSM-5 zeolites: activity towards no reduction and hydrocarbon oxidation

“…The presence of bands at around 212, 256 and a broad, but weak band between 600 and 850 nm can be observed. Itho et al 23 reported that the band at 212 nm, which appears in the spectra of all samples, is related to the zeolitic support and therefore not related to the Cu-species. The band at 256 nm is attributed to Cu 2+ interacting with oxygen atoms in the zeolite structure and the band between 600 and 850 nm to Cu 2+ cations in hexagonal coordination (this band is indicated in Figure 7 between arrows) 23,24 .…”

“…Itho et al 23 reported that the band at 212 nm, which appears in the spectra of all samples, is related to the zeolitic support and therefore not related to the Cu-species. The band at 256 nm is attributed to Cu 2+ interacting with oxygen atoms in the zeolite structure and the band between 600 and 850 nm to Cu 2+ cations in hexagonal coordination (this band is indicated in Figure 7 between arrows) 23,24 . Although the above discussed TPR-H 2 results suggest the presence of small amounts of CuO in the |Cu x |[Si y Al]-MFI catalysts, in their DRS-UV/VIS spectra there is no band at around 890 nm, which could indicate the presence of this species 25 .…”

An operando optical fiber UV–vis spectroscopic study of the catalytic decomposition of NO and N2O over Cu-ZSM-5

“…Alternatively, an absorption band at ca. 30,000 cm −1 could also be due to the presence of divalent copper species such as [CuOCu] 2+ , Cu 2+ O − and Cu 2+ O 2 − [40,58,60,61]. But, no clear bands at lower energy (d-d bands) are distinguished, making the presence of divalent copper species unlikely.…”