Atmospheric pressure chemical vapour deposition of boron doped titanium dioxide for photocatalytic water reduction and oxidation

Boron-doped titanium dioxide (B-TiO) films were deposited by atmospheric pressure chemical vapour deposition of titanium(iv) chloride, ethyl acetate and tri-isopropyl borate on steel and fluorine-doped-tin oxide substrates at 500, 550 and 600 °C, respectively. The films were characterised using powder X-ray diffraction (PXRD), which showed anatase phase TiO at lower deposition temperatures (500 and 550 °C) and rutile at higher deposition temperatures (600 °C). X-ray photoelectron spectroscopy (XPS) showed a dopant level of 0.9 at% B in an O-substitutional position. The ability of the films to reduce water was tested in a sacrificial system using 365 nm UV light with an irradiance of 2 mW cm. Hydrogen production rates of B-TiO at 24 μL cm h far exceeded undoped TiO at 2.6 μL cm h. The B-TiO samples were also shown to be active for water oxidation in a sacrificial solution. Photocurrent density tests also revealed that B-doped samples performed better, with an earlier onset of photocurrent. © 2013 The Owner Societies.

Structural and chemical embrittlement of grain boundaries by impurities: A general theory and first-principles calculations for copper

First-principles calculations of the Sigma 5(310)[001] symmetric tilt grain boundary in Cu with Bi, Na, and Ag substitutional impurities provide evidence that in the phenomenon of Bi embrittlement of Cu grain boundaries electronic effects do not play a major role; on the contrary, the embrittlement is mostly a structural or "size" effect. Na is predicted to be nearly as good an embrittler as Bi, whereas Ag does not embrittle the boundary in agreement with experiment. While we reject the prevailing view that "electronic" effects (i.e., charge transfer) are responsible for embrittlement, we do not exclude the role of chemistry. However, numerical results show a striking equivalence between the alkali metal Na and the semimetal Bi, small differences being accounted for by their contrasting "size" and "softness" (defined here). In order to separate structural and chemical effects unambiguously if not uniquely, we model the embrittlement process by taking the system of grain boundary and free surfaces through a sequence of precisely defined gedanken processes; each of these representing a putative mechanism. We thereby identify three mechanisms of embrittlement by substitutional impurities, two of which survive in the case of embrittlement or cohesion enhancement by interstitials. Two of the three are purely structural and the third contains both structural and chemical elements that by their very nature cannot be further unraveled. We are able to take the systems we study through each of these stages by explicit computer simulations and assess the contribution of each to the net reduction in intergranular cohesion. The conclusion we reach is that embrittlement by both Bi and Na is almost exclusively structural in origin; that is, the embrittlement is a size effect.

Tandem enzyme-catalysed reduction/cis-dihydroxylation of 2,2,2-trifluoroacetophenone: chemoenzymatic routes to new enantiopure phenol and benzylic alcohol reagents

Factors that control the competition between toluene dioxgenase-catalysed arene cis-dihydroxylation and dehydrogenase-catalysed ketone reduction have been studied, using whole cells of Pseudomonas putida UV and three alkylaryl ketones. The triol metabolite, obtained from 2,2,2-trifluoroacetophenone, has been used in the synthesis of single enantiomer chiral phenols and benzylic alcohols. Potential applications of the methylether derivatives of the chiral phenols and benzylic alcohols, as resolving agents, have been found. (c) 2007 Society of Chemical Industry.

Unusual voltammetry of the reduction of O-2 in [C(4)dmim][N(Tf)(2)] reveals a strong interaction of O-2(center dot-) with the [C(4)dmim](+) cation

Voltammetric studies of the reduction of oxygen in the room temperature ionic liquid [C(4)dmim][N(Tf)(2)] have revealed a significant positive shift in the back peak potential, relative to that expected for a simple electron transfer. This shift is thought to be due to the strong association of the electrogenerated superoxide anion with the solvent cation. In this work we quantitatively simulate the microdisc electrode voltammetry using a model based upon a one-electron reduction followed by a reversible chemical step, involving the formation of the [C(4)dmim](+)center dot center dot center dot O-2(center dot-) ion-pair, and in doing so we extract a set of parameters completely describing the system. We have simulated the voltammetry in the absence of a following chemical step and have shown that it is impossible to simultaneously fit both the forward and reverse peaks. To further support the parameters extracted from fitting the experimental voltammetry, we have used these parameters to independently simulate the double step chronoamperometric response and found excellent agreement. The parameters used to describe the association of the O-2(center dot-) with the [C(4)dmim](+) were k(f) = 1.4 x 10(3) s(-1) for the first-order rate constant and K-eq = 25 for the equilibrium constant.

On the complexity of the water-gas shift reaction mechanism over a Pt/CeO2 catalyst: Effect of the temperature on the reactivity of formate surface species studied by operando DRIFT during isotopic transient at chemical steady-state

The present report investigates the role of formate species as potential reaction intermediates for the WGS reaction (CO + H2O -> CO2 + H-2) over a Pt-CeO2 catalyst. A combination of operando techniques, i.e., in situ diffuse reflectance FT-IR (DRIFT) spectroscopy and mass spectrometry (MS) during steady-state isotopic transient kinetic analysis (SSITKA), was used to relate the exchange of the reaction product CO2 to that of surface formate species. The data presented here suggest that a switchover from a non-formate to a formate-based mechanism could take place over a very narrow temperature range (as low as 60 K) over our Pt-CeO2 catalyst. This observation clearly stresses the need to avoid extrapolating conclusions to the case of results obtained under even slightly different experimental conditions. The occurrence of a low-temperature mechanism, possibly redox or Mars van Krevelen-like, that deactivates above 473 K because of ceria over-reduction is suggested as a possible explanation for the switchover, similarly to the case of the CO-NO reaction over Cu, I'd and Rh-CeZrOx (see Kaspar and co-workers [1-3]). (c) 2006 Elsevier B.V. All rights reserved.

Electrochemical reduction of nitrobenzene and 4-nitrophenol in the room temperature ionic liquid [C(4)dmim][N(Tf)(2)]

The reductions of nitrobenzene and 4-nitrophenol were studied by cyclic voltammetry in the room temperature ionic liquid 1-butyl2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide [C(4)dmim][N(Tf)(2)] on a gold microelectrode. Nitrobenzene was reduced reversibly by one electron and further by two electrons in a chemically irreversible step. The more complicated reduction of 4-nitrophenol revealed three reductive peaks (two irreversible and one reversible) which were successfully simulated using the digital simulation program DigiSim((R)) using a mechanism of rapid self-protonation, given below.

CO oxidation and NO reduction on metal surfaces: density functional theory investigations

This article reviews the accumulated theoretical results, in particular density functional theory calculations, on two catalytic processes, CO oxidation and NO reduction on metal surfaces. Owing to their importance in automotive emission control, these two reactions have generated a lot of interest in the last 20 years. Here the pathways and energetics of the involved elementary reactions under different catalytic conditions are described in detail and the understanding of the reactions is generalized. It is concluded that density functional theory calculations can be applied to catalysis to elucidate mechanisms of complex surface reactions and to understand the electronic structure of chemical processes in general. The achieved molecular knowledge of chemical reactions is certainly beneficial to new catalyst design.

Selective catalytic reduction of O-2 with excess H-2 in the presence of C2H4 or C3H6

The selective reduction of molecular oxygen with excess H-2 in the presence of alkenes was achieved successfully for the first time: silver supported on alumina catalysts exhibited full conversion of O-2 at temperature as low as 50 degrees C, while the conversion of ethene or propene remained essentially zero up to 250 degrees C.

Facile biocatalytic reduction of the carbon-carbon double bond of 5-benzylidenethiazolidine-2,4-diones. Synthesis of ( )-5-(4-{2-[methyl(2-pyridyl)amino]ethoxy}benzyl)thiazolidine-2,4-dione (BRL 49653), its (R)-(+)-enantiomer and analogs.

Cantello, Barrier C. C.; Eggleston, Drake S.; Haigh, David; Haltiwanger, R. Curtis; Heath, Catherine M.; Hindley, Richard M.; Jennings, Keith R.; Sime, John T.; Woroniecki, Stefan R. SmithKline Beecham Pharmaceuticals, Surrey, UK. Journal of the Chemical Society, Perkin Transactions 1: Organic and Bio-Organic Chemistry (1994), (22), 3319-24. Publisher: Royal Society of Chemistry, CODEN: JCPRB4 ISSN: 0300-922X. Journal written in English. CAN 122:105736 AN 1995:237497 CAPLUS (Copyright (C) 2009 ACS on SciFinder (R)) Abstract A novel biotransformation system for the redn. of carbon-carbon double bonds in 5-benzylidenethiazolidine-2,4-diones to give the corresponding 5-benzylthiazolidine-1,4-diones, using whole cells of red yeasts, is described. These reduced compds., which are recovered in good yield, are of potential use in the treatment of non-insulin dependent diabetes mellitus. The mild reaction conditions developed allow redn. of 5-benzylidenethiazolidine-2,4-diones contg. other functionalities which are not compatible with alternative redn. methods. The biocatalytic redn. is enantioselective and the synthesis of R-(+)-5-(4-{2-[methyl(2-pyridyl)amino]ethoxy}benzyl)thiazolidine-2,4-dione by Rhodotorula rubra CBS 6469 and structure confirmation by X-ray crystallog. is detailed. Optimization of reaction conditions (including immobilization) for these whole cell redn. system is described.

The electrochemical reduction of the purines guanine and adenine at platinum electrodes in several room temperature ionic liquids

The reduction of guanine was studied by microelectrode voltammetry in the room temperature ionic liquids (RTILs) N-hexyltriethylammonium his (trifluoromethanesulfonyl) imide [N-6.2.2.2][N(Tf)(2)], 1-butyl-3-methylimidazolium hexafluorosphosphate [C(4)mim] [PF6], N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide [C(4)mpyrr][N(Tf)(2)], 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C-4mim][N(TF)(2)], N-butyl-N-methyl-pyrrolidinium dicyanamide [C(4)mpyrr][N(NC)(2)] and tris(P-hexyl)-tetradecylphosphonium trifluorotris(pentafluoroethyl)phosphate [P-14,P-6,(6,6)][FAP] on a platinum microelectrode. In [N-6,N-2,N-2,N-2][NTf2] and [P-14,P-6,P-6.6][FAP], but not in the other ionic liquids studied, guanine reduction involves a one-electron, diffusion-controlled process at very negative potential to produce an unstable radical anion. which is thought to undergo a dimerization reaction, probably after proton abstraction from the cation of the ionic liquid. The rate of this subsequent reaction depends on the nature of the ionic liquid, and it is faster in the ionic liquid [P-14,P-6,P-6.6[FAP], in which the formation of the resulting dimer can be voltammetrically monitored at less negative potentials than required for the reduction of the parent molecule. Adenine showed similar behaviour to guanine but the pyrimidines thymine and cytosine did not; thymine was not reduced at potentials less negative than required for solvent (RTIL) decomposition while only a poorly defined wave was seen for cytosine. The possibility for proton abstraction from the cation in [N-6,N-2,N-2,N-2],[NTF2] and [P-14,P-6,P-6.6][FAP] is noted and this is thought to aid the electrochemical dimerization process. The resulting rapid reaction is thought to shift the reduction potentials for guanine and adenine to lower values than observed in RTILs where the scope for proton abstraction is not present. Such shifts are characteristic of so-called EC processes where reversible electron transfer is followed by a chemical reaction. (C) 2009 Elsevier B.V. All rights reserved.

Evaluation of Pt and Re oxidation state in a pressurized reactor: difference in reduction between gas and liquid phase

Determination of metal oxidation state under relevant working conditions is crucial to understand catalytic behaviour. The reduction behaviour of Pt and Re was evaluated simultaneously as a function of support and solvent in a pressurized reactor (autoclave). The bimetallic catalysts are used in selective hydrogenation of carboxylic acids and amides. Gas phase reduction reduced the metals more efficiently, in particular Pt.

KINETICS OF REDUCTION OF HEXACYANOFERRATE(III) BY THIOSULFATE IONS MEDIATED BY RUTHENIUM DIOXIDE HYDRATE

The kinetics of reduction of hexacyanoferrate(III) by excess thiosulfate, mediated by RuO2.xH2O, are investigated. At high concentrations of S2O32- (0.1 mol dm-3) the kinetics of Fe(CN)63- reduction are first order with respect to [Fe(CN)63-] and [RuO2.xH2O] and independent of [Fe(CN)64-], [S2O32-] and [S4O62-]. At relatively low concentrations Of S2O32- (0.01 mol dm-3) and in the presence of appreciable concentrations of Fe(CN)64- and S4O62- (0.01 mol dm-3) the kinetics depend directly upon [Fe(CN)63-] and [RuO2.xH2O] and inversely upon [Fe(CN)64-]. Both sets of kinetics can be rationalised using an electrochemical model of redox catalysts in which a reversible reduction reaction [Fe(CN)63- + e- --> Fe(CN)64-] is coupled to an irreversible oxidation reaction (s2O32- - e- --> 1/2S4O62-), by a dispersion of RuO2.xH2O microelectrodes. At high concentrations Of S2O32- this model predicts that the kinetics of Fe(CN)63- reduction are controlled by the rate of diffusion of the Fe(CN)63- ions to the RuO2.xH2O particles. The kinetics observed at low concentrations of S2O32- are predicted by the electrochemical model, assuming that the Tafel slope for the oxidation Of S2O32- to S4O62- on the RuO2.xH2O particles is 56.4 mV decade-1.