Reactivity of photoinduced hole centers on anatase and activation of molecular oxygen

Volodin, Alexander M.; Черкашин, А. Е.; Захаренко, В. С.

doi:10.1007/bf02067839

Cited by 8 publications

(10 citation statements)

References 7 publications

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“…The quantum yield of POIE at 420 nm is ∼30 times higher than in the UV region. The obtained spectral dependence is close to the dependence of O – creation measured by EPR in refs − .…”

Section: Results and Discussionsupporting

confidence: 87%

Spectral Features of Photostimulated Oxygen Isotope Exchange and NO Adsorption on “Self-Sensitized” TiO_2–x/TiO₂ in UV–Vis Region

2014

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We have investigated the photoactivated O 2 adsorption/desorption, the isotope equilibration (POIEq), and the isotope exchange (POIEx) in the O 2 −(TiO 2−x /TiO 2 ) (Degussa P-25) system, as well as the adsorption and POIEx in the NO−(TiO 2−x /TiO 2 ) systems. The photoactivation spectra of the hole centers O s − generation, of POIEq, and of the NO photoadsorption were measured in the 300−500 nm range using a continuously adjustable wavelength light source. The spectral characteristics of the NO photoadsorption are close to those of POIEq Both electron-donor and hole centers are manifested in these processes. For O 2 photodesorption, CO oxidation, POIEx, and POIEq the hole centers O s − are responsible. In the case of O 2 and NO photoadsorption both types of centers are active. The maxima of POIEq and of NO photoadsorption are placed near 420 nm beyond the edge of the TiO 2 bandgap absorption. It was found that not only does the N 18 O−Ti 16 O 2 exchange occurs under the illumination but also it can be activated by a preliminary sample illumination in vacuum as it was observed for POIEq. The photoactivation spectrum does not coincide with the absorption spectra of the F-type centers (F + and F-centers, i.e., oxygen anion vacancies filled with one or two e − , respectively) and of Ti 3+ . The formation of the 2D structures, "core−shell" TiO 2−x /TiO 2 , on the parts of the surface region and the decreasing of bandgap on these parts are supposed based on the kinetic data (the "fast" excitations in the bulk under UV irradiation and the "slow" excitations on the surface under the visible irradiation) and on the spectral data (maximum action is near 420 nm for both electronic and hole centers).

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Section: Results and Discussionsupporting

confidence: 87%

Spectral Features of Photostimulated Oxygen Isotope Exchange and NO Adsorption on “Self-Sensitized” TiO_2–x/TiO₂ in UV–Vis Region

2014

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“…In particular, it was shown that atomic oxygen radicals O – on VO x /SiO 2 reacted with H 2 , CO, C 2 H 4 , or C 6 H 6 , at very low temperatures and formed surface ozonide radicals O 3 – after adsorption of molecular oxygen at liquid nitrogen temperature. Similar reactions were reported for O – radical anions on the surface of MgO, ZnO, and TiO 2 . ,, It was also reported that the active oxygen species accounting for oxidation of benzene to phenol over Fe-ZSM-5 catalysts are O – radical anions stabilized on Fe 3+ cations . In addition to reaction with benzene, these species can initiate homolytic splitting of methane and hydrogen , and oxygen exchange at low temperatures. , …”

Section: Discussionsupporting

confidence: 67%

“…Similar reactions were reported for O − radical anions on the surface of MgO, ZnO, and TiO 2 . 3,62,63 It was also reported that the active oxygen species accounting for oxidation of benzene to phenol over Fe-ZSM-5 catalysts are O − radical anions stabilized on Fe 3+ cations. 24 In addition to reaction with benzene, these species can initiate homolytic splitting of methane and hydrogen 64,65 and oxygen exchange at low temperatures.…”

Section: Formation Of Surface Paramagnetic Species (O 2 )mentioning

confidence: 99%

Electronic Structure of Oxygen Radicals on the Surface of VO_x/TiO₂Catalysts and Their Role in Oxygen Isotopic Exchange

Avdeev

Bedilo

2013

J. Phys. Chem. C

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The electronic structure of oxygen radicals formed by adsorption of gas-phase oxygen on partially reduced sites of supported vanadium oxide catalyst V4+O x /TiO2 has been studied by periodic DFT. The unpaired electron density in the radicals is transferred from the paramagnetic V4+(3d1) ion to the adsorbed oxygen atoms resulting in the formation of surface oxygen radicals: atomic O–, superoxide O2 –, and ozonide O3 –. These radical species exhibit higher reactivity compared to the surface oxygen species stabilized on fully oxidized diamagnetic V5+(3d0) ions. Oxygen isotopic exchange over O– radicals has been investigated by the climbing image nudged elastic band (CI-NEB) method. We show that molecular oxygen can exchange with the lattice oxygen of the surface paramagnetic radicals V5+O– with low activation energy of about 14 kcal/mol, close to the value experimentally observed for some heterolytic R1 oxygen exchange reactions on vanadia catalysts. The obtained data suggest that O– radicals formed as short-lived intermediates at elevated temperatures are likely to be the active sites of the oxygen exchange following the R1 mechanism. The properties of oxygen radicals and their possible role in catalytic oxidation processes taking place over bulk and supported metal oxide catalysts are discussed. It is suggested that oxygen radicals can be the active species in catalytic oxidation reactions.

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“…The creation of trapped holes O – in TiO 2 , − TiO 2 /SiO 2 was detected by EPR in 110–140 K range under UV irradiation, and a consequent admission of oxygen onto TiO 2 led to the appearance of O 3 – on the surface accompanied by the decrease of O – signal . The nature of O – is considered, on one hand, as adsorbed atomic oxygen species O ads – formed during dissociative oxygen adsorption or, on the other hand, as oxygen O s – in the TiO 2 structure, , resulting from the following reactions: TiO 2 + italich ν .25em ( > 3.2 eV ) → normale − + normalh + O s 2 − + normalh + → O s − …”

Section: Introductionmentioning

confidence: 99%

“…The interaction of oxygen with photoactivated TiO 2 is a conventional model reaction for the test of surface species activity. The species formed on TiO 2 surface upon UV irradiation in oxygen are widely investigated by means of EPR, and they are mainly O 2 – , O – and O 3 – . − It is usually believed that molecular species O 2 – is a “fingerprint” of reduced TiO 2 formed via the electron e ‑ transfer from a Ti 3+ ion to an oxygen molecule . This species is stable on the (110) rutile surface and Degussa P-25 powder until 410 K. A recent paper calls the relationship between the amount of molecular species and the degree of TiO 2 reduction in question supposing that the formation of O 2 – is determined rather by the prehistory of the sample and is related to the bond formation between oxygen and an interstitial Ti ion.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Photostimulated Oxygen Isotope Exchange on TiO₂ Degussa P25 Surface upon UV–Vis Irradiation.

2012

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The interaction of oxygen molecules with TiO 2 (Degussa P25) surface under UV (λ = 365 nm) and vis (λ = 436 nm) irradiation at T = 293 K was investigated by means of massspectrometry and thermo-programmed desorption (TPD) spectroscopy. Oxygen chemisorbed on reduced TiO 2 surface consists of molecular species O 2 − and atomic ones. The adsorbed O 2 species which are stable at 293 K are not observed on oxidized TiO 2 . The UV or vis irradiation in 18 O enriched oxygen induces an intensive photostimulated oxygen isotope equilibration (POIEq) and exchange (POIEx) via a weakly bonded intermediate O 3 − due to the interaction of 18 O 2 with a hole center O s − (which is an exchangeable anion O s 2− that captured a photogenerated hole h + ). The number of surface exchangeable oxygen anions is ∼2 × 10 11 cm −2 for oxidized TiO 2 and ∼10 8 cm −2 for reduced TiO 2 . There is a reason to consider the observed POIEq as a multiple interaction of O s − with 18 O 2 molecules (in fact by means of heteroexchange). Thus, the obtained POIEq rate corresponds to the number of O s − centers, while the POIEx rate is proportional to the rate of O s − formation. The kinetics of activation/deactivation of O s − in POIEq was studied in the flow-through mode (at 10 −6 −10 −3 Torr). Under vis irradiation, the hole centers O s − are formed in noticeable quantities and live for hundreds of seconds at T = 293 K, while the UV light transforms only a small part of all possible O s 2− into O s − . The lifetime of the latter is short. The lifetime of O s − reduces with the increase of temperature or O 2 pressure. Two pathways of O s − deactivation are supposed: the first one includes the recombination of O s − with an electron with an estimated energetic barrier E des = (0.35 ± 0.06) eV; and the second one is a result of collision of intermediate O 3 − with gaseous O 2 .

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Reactivity of photoinduced hole centers on anatase and activation of molecular oxygen

Cited by 8 publications

References 7 publications

Spectral Features of Photostimulated Oxygen Isotope Exchange and NO Adsorption on “Self-Sensitized” TiO_2–x/TiO₂ in UV–Vis Region

Spectral Features of Photostimulated Oxygen Isotope Exchange and NO Adsorption on “Self-Sensitized” TiO_2–x/TiO₂ in UV–Vis Region

Electronic Structure of Oxygen Radicals on the Surface of VO_x/TiO₂Catalysts and Their Role in Oxygen Isotopic Exchange

Investigation of Photostimulated Oxygen Isotope Exchange on TiO₂ Degussa P25 Surface upon UV–Vis Irradiation.

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Reactivity of photoinduced hole centers on anatase and activation of molecular oxygen

Cited by 8 publications

References 7 publications

Spectral Features of Photostimulated Oxygen Isotope Exchange and NO Adsorption on “Self-Sensitized” TiO2–x/TiO2 in UV–Vis Region

Spectral Features of Photostimulated Oxygen Isotope Exchange and NO Adsorption on “Self-Sensitized” TiO2–x/TiO2 in UV–Vis Region

Electronic Structure of Oxygen Radicals on the Surface of VOx/TiO2Catalysts and Their Role in Oxygen Isotopic Exchange

Investigation of Photostimulated Oxygen Isotope Exchange on TiO2 Degussa P25 Surface upon UV–Vis Irradiation.

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Spectral Features of Photostimulated Oxygen Isotope Exchange and NO Adsorption on “Self-Sensitized” TiO_2–x/TiO₂ in UV–Vis Region

Spectral Features of Photostimulated Oxygen Isotope Exchange and NO Adsorption on “Self-Sensitized” TiO_2–x/TiO₂ in UV–Vis Region

Electronic Structure of Oxygen Radicals on the Surface of VO_x/TiO₂Catalysts and Their Role in Oxygen Isotopic Exchange

Investigation of Photostimulated Oxygen Isotope Exchange on TiO₂ Degussa P25 Surface upon UV–Vis Irradiation.