Insights into the active surface species formed on Ta2O5 nanotubes in the catalytic oxidation of CO

Abstract

Freestanding Ta2O5 nanotubes were prepared by an anodizing method. As-anodized amorphous nanotubes were calcined at high temperature to obtain a crystalline phase. All materials were studied by means of BET analysis, XRD, TEM, SEM, XPS, and FTIR and were evaluated in the catalytic oxidation of CO. An XPS study confirmed the formation of different tantalum surface species after high temperature treatment of amorphous Ta2O5 nanotubes. Calcination at 800 °C generated Ta(4+) while higher temperature (1000 °C) treatment led to the formation of Ta(3+) species. These materials also showed significant differences in catalytic activity. Higher activity was observed for samples calcined at 800 °C than at 1000 °C, suggesting that Ta(4+) species are active sites for CO oxidation.

Colossal permittivity behavior and its origin in rutile (Mg1/3Ta2/3)xTi1-xO2

“…Figure 1b shows the presence of doublet Ta 5+ 4 f peaks with binding energies at 28.0 eV and 26.1 eV, respectively. Their spin-orbit splitting of 1.9 eV is consistent with that of the Ta 2 O 5 as reported in the literature 31, 32 . The Ta 4 f signal suggests that Ta has a normal state of +5 without any reduction.…”

Quantitative prediction of the structure and properties of Li2O–Ta2O5–SiO2 glasses via phase diagram approach

“…As Li 2 O concentration increases to 40 mol%, the vibration of Si–O with two nonbridging oxygens per SiO 4 tetrahedron (Si–O–2NBO) appears at 840 cm −1 due to the addition of Q 2 in Li 2 SiO 3 structure . Furthermore, the band located at 650 cm −1 is observed in Figure B after the addition of Ta 2 O 5 , which is closely related to the symmetric stretching mode of Ta–O–Ta, and the intensity increases gradually with increasing Ta 2 O 5 content from 10 to 30 mol%. Obviously, FTIR spectra of (100− x )S x L and (70− y )S30L y T glasses before and after heat treatment approximately coincide with the exception of sample 40S30L30T.…”

Fabrication of Durable Ordered Ta2O5 Nanotube Arrays Decorated with Bi2S3 Quantum Dots

“…The sample NTs_15 V_5 min_Air_450 °C_1 h, on the other hand, exhibits a larger concentration of fluorine compounds, which originated from the preparation procedure. The Ta 2 O 5 NTs are well-characterized by the main Ti 5+ fraction of the Ta 4f spectra (Ta 4f 7/2 signal at 26.4 eV) [37,38,39,40]. We also note a small contribution of Ta 1+ and Ta 0 surface species [39,40] (Table S1).…”

“…The Bi 4f spectra revealed three chemical states of Bi Bi 0 , Bi 2 S 3 , and Bi 2 O 3 , represented by the Bi 4f 7/2 signals at 157.0, 158.0, and 159.5 eV, respectively [37]. Unfortunately, the Bi 4f spectra are partially overlapped by the S 2p signals attributed to sulfide and sulfate species (S 2p 3/2 signals located at 163.5 and 168.5 eV, respectively [38]). Additionally, in the binding energy (BE) range of Ta 4f spectra, additional signals of the Bi 3d and O 2s are detected (Figure 2).…”

“…The Bi 4f spectrum shows the Bi 2 S 3 fraction as a major contribution of Bi species and the Ta 4f spectrum is overlapped by the strong Bi 5d signals. Moreover, the sulfate fraction of S 2p is not detected and instead of the main O 1s signal related to Ta 2 O 5 (BE close to 530.5 eV [38,41,42], a weaker oxygen peak appears in the O 1s spectrum (at 529.9 eV), which is characteristic for the Bi–O bond [37].…”