Active sites and effects of H2O and temperature on the photocatalytic oxidation of 13C-acetic acid on TiO2

Backes, Michael J.; Lukaski, Adrienne C.; Muggli, Darrin S.

doi:10.1016/j.apcatb.2005.03.012

Cited by 46 publications

(57 citation statements)

References 34 publications

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“…[18] In the carboxylate region, five bands at 1300, 1430, 1472, 1532, and 1690 cm À1 were also identified. Based on previous studies of the identification of absorption bands in the DRIFTS spectrum of acetic acid adsorbed on TiO 2 and considering the structure similarity between acetic acid and propionic acid, [19] these bands can be individually assigned. That is, the bands at 1300 and 1690 cm À1 represent molecularly adsorbed propionic acid, while the bands at 1430, 1472, and 1532 cm À1 can be attributed to dissociated propionate.…”

Section: Resultsmentioning

confidence: 99%

An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study

Wen

Chen

et al. 2010

Chemistry A European J

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The aerobic decarboxylation of saturated carboxylic acids (from C(2) to C(5)) in water by TiO(2) photocatalysis was systematically investigated in this work. It was found that the split of C(1)-C(2) bond of the acids to release CO(2) proceeds sequentially (that is, a C(5) acid sequentially forms C(4) products, then C(3) and so forth). As a model reaction, the decarboxylation of propionic acid to produce acetic acid was tracked by using isotopic-labeled H(2)(18)O. As much as ≈42% of oxygen atoms of the produced acetic acids were from dioxygen ((16)O(2)). Through diffuse reflectance FTIR measurements (DRIFTS), we confirmed that an intermediate pyruvic acid was generated prior to the cut-off of the initial carboxyl group; this intermediate was evidenced by the appearance of an absorption peak at 1772 cm(-1) (attributed to C=O stretch of α-keto group of pyruvic acid) and the shift of this peak to 1726 cm(-1) when H(2)(16)O was replaced by H(2)(18)O. Consequently, pyruvic acid was chosen as another model molecule to observe how its decarboxylation occurs in H(2)(16)O under an atmosphere of (18)O(2). With the α-keto oxygen of pyruvic acid preserved in the carboxyl group of acetic acid, ≈24% new oxygen atoms of the produced acetic acid were from molecular oxygen at near 100% conversion of pyruvic acid. The other ≈76% oxygen atoms were provided by H(2)O through hole/OH radical oxidation. In the presence of conduction band electrons, O(2) can independently accomplish such C(1)-C(2) bond cleavage of pyruvic acid to generate acetic acid with ≈100% selectivity, as confirmed by an electrochemical experiment carried out in the dark. More importantly, the ratio of O(2) participation in decarboxylation increased along with the increase of pyruvic acid conversion, indicating the differences between non-substituted acids and α-keto acids. This also suggests that the O(2)-dependent decarboxylation competes with hole/OH-radical-promoted decarboxylation and depends on TiO(2) surface defects at which Ti(4c) sites are available for the simultaneous coordination of substrates and O(2).

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Section: Resultsmentioning

confidence: 99%

An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study

Wen

Chen

et al. 2010

Chemistry A European J

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“…Groups have undertaken mechanistic studies of this adsorbate on both single crystal [701,777,[967][968][969] and high surface area [734,790,966,[970][971][972][973] TiO 2 . Starting with the latter case, Nosaka et al [734] have proposed both hole-mediated and OH•-mediated photodecomposition mechanisms for adsorbed acetate.…”

Section: Carboxylic Acidsmentioning

confidence: 99%

A surface science perspective on TiO2 photocatalysis

Henderson

2011

Surface Science Reports

1,855

1,634

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a b s t r a c tThe field of surface science provides a unique approach to understanding bulk, surface and interfacial phenomena occurring during TiO 2 photocatalysis. This review highlights, from a surface science perspective, recent literature that provides molecular-level insights into photon-initiated events occurring at TiO 2 surfaces. Seven key scientific issues are identified in the organization of this review. These are: (1) photon absorption, (2) charge transport and trapping, (3) electron transfer dynamics, (4) the adsorbed state, (5) mechanisms, (6) poisons and promoters, and (7) phase and form. This review ends with a brief examination of several chemical processes (such as water splitting) in which TiO 2 photocatalysis has made significant contributions in the literature.

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“…centers, it will be directly transformed into formaldehyde without being oxidized to acetic acid. Subsequent steps are the same in both cases: formic acid and finally CO 2 will be produced [24,25]. It was found that direct hole-oxidation of acetaldehyde is not the only possible pathway: there is a significant contribution of radical mediated chain reactions (by OH Á and other oxygen containing radicals) [24,26].…”

Section: Resultsmentioning

confidence: 96%

Comparison of the liquid and gas phase photocatalytic activity of flame-synthesized TiO2 catalysts: the role of surface quality

Balázs

Gácsi

Pallagi

et al. 2011

Reac Kinet Mech Cat

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A set of flame-hydrolytic TiO 2 samples was synthesized. Via systematically increasing the precursor (TiCl 4 ) feeding rate to the flame, nanocrystalline TiO 2 specimens with practically identical bulk structural properties (that is: particle size, anatase-to-rutile ratio, specific surface area) were obtained. However, it has been observed that with increasing precursor feed rate, the fraction of the polyhedral particles increased in the products at the expense of the spherical ones. In our previous work, we argued, that faceted particles are superior to spherical ones in phenol decomposition. In this work, the photocatalytic activities of these samples were determined in the gas phase using methanol and acetaldehyde as model compounds and they were compared with those obtained for an aqueous solution containing phenol. The photocatalytic activities were found to vary in parallel in the case of phenol and methanol: they increased with the precursor feed rate (and also with the frequency of the faceted nanocrystals) for both. However, for acetaldehyde, the photocatalytic activity did not change systematically within this series of experiments, and roughly remained constant. Our results indicate that the surface quality of TiO 2 is of primary importance in the selectivity of photocatalytic reactions.

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Active sites and effects of H2O and temperature on the photocatalytic oxidation of 13C-acetic acid on TiO2

Cited by 46 publications

References 34 publications

An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study

An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study

A surface science perspective on TiO2 photocatalysis

Comparison of the liquid and gas phase photocatalytic activity of flame-synthesized TiO2 catalysts: the role of surface quality

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Active sites and effects of H2O and temperature on the photocatalytic oxidation of 13C-acetic acid on TiO2

Cited by 46 publications

References 34 publications

An Unexplored O2‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO2 Photocatalysis: An Isotopic Probe Study

An Unexplored O2‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO2 Photocatalysis: An Isotopic Probe Study

A surface science perspective on TiO2 photocatalysis

Comparison of the liquid and gas phase photocatalytic activity of flame-synthesized TiO2 catalysts: the role of surface quality

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An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study

An Unexplored O₂‐Involved Pathway for the Decarboxylation of Saturated Carboxylic Acids by TiO₂ Photocatalysis: An Isotopic Probe Study