IR studies of coadsorption of organic molecules and CO on Cu+ cations in zeolites

Dátka, Jerzy; Kukulska–Zając, Ewa; Kobyzewa, W.

doi:10.1016/j.cattod.2006.01.011

Cited by 14 publications

(7 citation statements)

References 15 publications

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“…Lowering the CO stretching frequency is the result of electron transfer from the ethanol molecule to Cu + ion and the more efficient effect of π-back donation of d-electrons of Cu + to π * antibonding orbitals of CO. Similar effects were observed in earlier studies of coadsorption of other molecules, such as but-1-ene, benzene, acetone and CO on Cu + in CuZSM-5 [ 44 ]. Two bands assigned to Cu + exch interacting simultaneously with CO and ethanol molecules (2118 and 2134 cm −1 ) suggested the occurrence of two kinds of Cu + exch ions of different electrondonor properties.…”

Section: Resultssupporting

confidence: 87%

Oxidation of Ethanol in Cu-Faujasites Studied by IR Spectroscopy

2021

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In this study, IR studies of the coadsorption of ethanol and CO on Cu+ cations evidenced the transfer of electrons from ethanol to Cu+, which caused the lowering of the frequency of the band attributed to CO bonded to the same Cu+ cation due to the more effective π back donation of d electrons of Cu to antibonding π* orbitals of CO. The reaction of ethanol with acid sites in zeolite HFAU above 370 K produced water and ethane, polymerizing to polyethylene. Ethanol adsorbed on zeolite Cu(2)HFAU containing acid sites and Cu+exch also produced ethene, but in this case, the ethene was bonded to Cu+ and did not polymerize. C=C stretching, which is IR non-active in the free ethene molecule, became IR active, and a weak IR band at 1538 cm−1 was present. The reaction of ethanol above 370 K in Cu(5)NaFAU zeolite (containing small amounts of Cu+exch and bigger amounts of Cu+ox, Cu2+exch and CuO) produced acetaldehyde, which was further oxidized to the acetate species (CH3COO-). As oxygen was not supplied, the donors of oxygen were the Cu species present in our zeolite. The CO and NO adsorption experiments performed in Cu-zeolite before and after ethanol reaction evidenced that both Cu+ox and Cu2+ (Cu2+exch and CuO) were consumed by the ethanol oxidation reaction. The studies of the considered reaction of bulk CuO and Cu2O as well as zeolites, in which the contribution of Cu+ox species was reduced by various treatments, suggest that ethanol was oxidized to acetaldehyde by Cu2+ox (the role of Cu+ox could not be elucidated), but Cu+ox was the oxygen donor in the acetate formation.

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Section: Resultssupporting

confidence: 87%

Oxidation of Ethanol in Cu-Faujasites Studied by IR Spectroscopy

2021

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“…6–8 cm −1 ). The situation is different from that of “typical” zeolite CuY (Si/Al = 2.5), in which two Cu exch + –CO bands at 2140 and 2160 cm −1 were observed [53,54]. An analogous situation concerns Si–OH–Al groups.…”

Section: Resultsmentioning

confidence: 70%

IR Studies of the Cu Ions in Cu-Faujasites

et al. 2019

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The properties of Cu ions in dealuminated faujasite-type zeolites (Si/Al = 31) containing 1, 2, and 5 wt.% of Cu were investigated by IR spectroscopy with CO and NO as probe molecules. Cu was introduced by impregnation into zeolites in both protonic (HFAU) and sodium (NaFAU) forms of zeolite. Four kinds of Cu species were found: Cu+exch., Cu+oxide, Cu2+exch. (square, planar, and square pyramidal), and Cu2+oxide (CuO). The proportions between these four kinds of Cu depended on the amount of Cu and on the form of zeolite to which Cu was introduced (HFAU or NaFAU). Zeolites with 1 wt.% of Cu introduced to HFAU (denoted as Cu(1)HFAU) contained only Cu+exch., whereas other forms of Cu were present in zeolites of higher Cu contents. The concentration of Cu+exch. was determined by quantitative IR studies of CO adsorption. According to the IR results, some Cu ions were situated inside hexagonal prisms and/or cuboctahedra, and were inaccessible to adsorbed molecules. IR studies also evidenced that Cu ions in oxide forms—Cu+oxide and Cu2+oxide (CuO)—were better electron donors than Cu in exchange positions (Cu+exch. and Cu2+exch).

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“…The CO band is shifted from 2157 cm -1 (without formaldehyde) to 2136 cm -1 if both formaldehyde and CO are bonded to the same Cu + cation. The ∆ν value (∆ν ) 21 cm -1 ) for formaldehyde is lower than the corresponding frequency shift if acetone (∆ν ) 27 cm -1 ) and CO interacted with the same Cu + cation (Figure 3, spectrum c, taken from our previous study 30 ).…”

Section: Resultsmentioning

confidence: 94%

Transformations of Formaldehyde Molecules in Cu−ZSM-5 Zeolites

Kukulska–Zając

Dátka

2007

J. Phys. Chem. C

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The activation of CdO bond in formaldehyde molecule was followed by IR spectroscopy. IR studies showed that the interaction of formaldehyde with Cu + weakens of the CdO bond and results in a red shift of the CdO IR band (∆ν ) 56 cm -1 ). The activation of the CdO bond is the result of π back-donation of d electrons of Cu + to π * antibonding orbitals of the molecule. Experiments on coadsorption of formaldehyde and CO on the same Cu* showed that formaldehyde acts as electron donor to the Cu + -CO system, resulting in stronger π back-donation to antibonding orbitals of CO. IR studies showed that formaldehyde molecules sorbed in zeolite Cu-ZSM-5 are oxidized to formate ions. Cu 2+ ions, which survived the self-reduction to Cu + during the pretreatment of zeolite under vacuum, were oxidant. Such Cu 2+ ions are reduced to Cu + during the reaction with formaldehyde molecules.

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IR studies of coadsorption of organic molecules and CO on Cu+ cations in zeolites

Cited by 14 publications

References 15 publications

Oxidation of Ethanol in Cu-Faujasites Studied by IR Spectroscopy

Oxidation of Ethanol in Cu-Faujasites Studied by IR Spectroscopy

IR Studies of the Cu Ions in Cu-Faujasites

Transformations of Formaldehyde Molecules in Cu−ZSM-5 Zeolites

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