TPR, ESR, and XPS Study of Cu2+Ions in Sol–Gel-Derived TiO2

Córdoba, G.; Viniegra, M.; Fierro, J. L. G.; Padilla, Juan; Arroyo, R.

doi:10.1006/jssc.1997.7690

Cited by 63 publications

(34 citation statements)

References 29 publications

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“…Figure 7 shows the EPR spectra of adsorbed alcohols on Nb 2 O 5 or Cu/Nb 2 O 5 under photoirradiation at 77 K. UV irradiation to 1-pentanol adsorbed on bare Nb 2 O 5 resulted in the appearance of an EPR signal assigned to the corresponding alkoxide carbon radical [1b] at 77 K (Figure 7 a). In the case of 1-pentanol adsorbed on Cu/Nb 2 O 5 , however, a broad signal assigned to the Cu II ion [15] appeared, whereas no signal assignable to an organic radical was detected. On the other hand, when tertiary butyl alcohol adsorbed on Nb 2 O 5 or Cu/Nb 2 O 5 under UV irradiation at 77 K, an intense signal (g = 2.003, A H = 2.0 mT) assigned to the methyl radical [16] was found predominantly, regardless of the presence of copper (Figures 7 c,d).…”

Section: Investigation Of the Excitation Mechanism By Dft Calculationsmentioning

confidence: 73%

Reaction Mechanism and the Role of Copper in the Photooxidation of Alcohol over Cu/Nb₂O₅

et al. 2011

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Loading of a small amount of copper on Nb(2)O(5) significantly enhances the activity of alcohol photooxidation without organic solvents. Alcohol is adsorbed on the Lewis acid site (Nb(V)) to form an alkoxide species. Photogenerated holes and electrons on Cu/Nb(2)O(5) are trapped by the adsorbed alkoxide and Cu(II) species to form the alkoxide carbon radical and Cu(I) species. The formed alkoxide carbon radical is converted to a carbonyl compound and then desorbed. Finally, the reduced Cu(I) sites are reoxidized by reaction with O(2). The alcohol photooxidation over Nb(2)O(5) takes place under not only UV irradiation but also under visible light irradiation up to 450 nm, although the band gap of Nb(2)O(5) is 390 nm (3.2 eV). DFT calculations reveal that 1) the surface donor level derived from the adsorbed alkoxide species is located in the forbidden band, 2) direct electron transition from the surface donor level to the conduction band takes place by absorbing a photon, 3) the excitation energy from surface donor level to the Nb 4d conduction band is lower than that from the O 2p valence band to Nb 4d. The kinetic study and FT/IR spectra suggest that Cu(I) acts as an effective desorption site for the products. Based on these results, we conclude that copper functions as an effective redox promoter and desorption site for the product.

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Section: Investigation Of the Excitation Mechanism By Dft Calculationsmentioning

confidence: 73%

Reaction Mechanism and the Role of Copper in the Photooxidation of Alcohol over Cu/Nb₂O₅

et al. 2011

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“…The BE in the 532.2-532.6 eV region is typical of O 1s in a silica environment. [40,41,42] In sample sSi Cu1, the BE values of the Cu 2p region are slightly higher than in the other samples (934.7 eV), and this finding can be ascribed, according to observations made by other authors also, [23,24,43,44] to an interaction with the support oxide, which in turn would demonstrate the fine dispersion of the copper species. If CuO were present in an agglomerate state, the BE typical of bulk CuO would be observed instead.…”

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confidence: 79%

“…In this case, the presence of well-dispersed Cu II species interacting with the OH groups of the silica support (935.3 eV) could be inferred. [24,43] XRD and TEM measurements shed some light on the microstructure of the materials.…”

mentioning

confidence: 99%

Nanostructured Copper Oxide on Silica–Zirconia Mixed Oxides by Chemical Implantation

Dell’Amico

Bertagnolli

Calderazzo

et al. 2009

Chemistry A European J

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“…When the sample is heated at 500°C in argon atmosphere, the signal due to Cu 2 + ions disappears and a new signal at g = 2.002 appears. This ESR signal, which is present in all heated samples, is due to the conduction electrons that are present only in small nanocrystallites (7 nm or smaller) [9,10], which indicates that the copper ions were reduced. These results show that Cu 2 + ions are not directly responsible of the change in the phase transition temperature.…”

Section: Resul Ts and Discusionmentioning

confidence: 95%

Anatase-Rutile Phase Transformation of Cu2+ Doped TiO2 in a Non-Reducing Atmosphere

Córdoba

Padilla

Lara

et al. 2003

Emerging Fields in Sol-Gel Science and Technology

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The anatase-rutile phase transformation of Ti02 containing various amounts of ci+ ions was investigated in argon atmosphere by means of xray diffraction and electron spin resonance spectroscopy. The samples were prepared by the sol-gel method from titanium(lV) isopropoxide and copper(II) nitrate. The amorphous samples were calcined in argon atmosphere for 2 h at different temperatures. In the presence of Cu 2 +, the anatase-rutile transition temperature is lower than the corresponding one in pure Ti02. The transformation in argon atmosphere changes the transition temperatures due to the spontaneous reduction of Cu 2 + and Ti 4 + ions to metallic copper and Ti 3 + respectively. The broadening of the electron spin resonance spectra from this ion show that Ti 3 + ions are present in different sites into the Ti02 lattice. This are confirmed by electron spin resonance and allowed liS to follow the phase transformation in detail.

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TPR, ESR, and XPS Study of Cu2+Ions in Sol–Gel-Derived TiO2

Cited by 63 publications

References 29 publications

Reaction Mechanism and the Role of Copper in the Photooxidation of Alcohol over Cu/Nb₂O₅

Reaction Mechanism and the Role of Copper in the Photooxidation of Alcohol over Cu/Nb₂O₅

Nanostructured Copper Oxide on Silica–Zirconia Mixed Oxides by Chemical Implantation

Anatase-Rutile Phase Transformation of Cu2+ Doped TiO2 in a Non-Reducing Atmosphere

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TPR, ESR, and XPS Study of Cu2+Ions in Sol–Gel-Derived TiO2

Cited by 63 publications

References 29 publications

Reaction Mechanism and the Role of Copper in the Photooxidation of Alcohol over Cu/Nb2O5

Reaction Mechanism and the Role of Copper in the Photooxidation of Alcohol over Cu/Nb2O5

Nanostructured Copper Oxide on Silica–Zirconia Mixed Oxides by Chemical Implantation

Anatase-Rutile Phase Transformation of Cu2+ Doped TiO2 in a Non-Reducing Atmosphere

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Reaction Mechanism and the Role of Copper in the Photooxidation of Alcohol over Cu/Nb₂O₅

Reaction Mechanism and the Role of Copper in the Photooxidation of Alcohol over Cu/Nb₂O₅