Photocatalytic performance of combustion synthesized β-Ga2O3 for the degradation of tri-n-butyl phosphate in aqueous solution

Nanostructures of β-Ga₂O₃ were prepared by solution combustion route using urea as the fuel. Transmission electron microscopic measurements and powder X-ray diffraction measurements confirmed the crystalline nature of β-Ga₂O₃ with particle size in the range of 10–15 nm. Surface area measurements indicated that the synthesized semiconductor catalyst had a specific surface area of 30 m²/g. In this work, photocatalytic degradation studies of tri-n-butyl phosphate using nano sized β-Ga₂O₃ is presented. A cylindrical photoreactor was used for the degradation studies and gas chromatographic estimation was adopted to follow the extent of degradation. Complete degradation of tributyl phosphate could be achieved in less than 40 min using 10 mg of photocatalyst and 0.5 mL of H₂O₂ for 1000 mL of 400 ppm TBP. Degradation of TBP was found to follow pseudo first order kinetics and the rate of TBP degradation was found to be superior for β-Ga₂O₃ photocatalyst compared to P-25 TiO₂.     

Magnetically recyclable Pd/γ-AlOOH@Fe_3O_4 catalysts and their catalytic performance for the Heck coupling reaction

Novel magnetically recyclable Pd/γ-AlOOH@Fe3O4 catalysts were prepared using γ-AlOOH@Fe3O4 as a magnetic supporter and nano-Pd particles as the active catalytic component.The structure of the catalysts was characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),N2 adsorption-desorption,and a vibration sample magnetometer(VSM).The catalytic activity and recyclability for the Heck coupling reaction were investigated.Results showed that the magnetic γ-AlOOH@Fe3O4 possessed a core-shell structure,as well as that the nano-Pd particles were 6–8 nm and had been well dispersed in the γ-AlOOH shell.In the Heck coupling reactions,the magnetic Pd/γ-AlOOH@Fe3O4 catalysts exhibited good catalytic activity and recyclability.For the(0.021 mol%)Pd/γ-AlOOH@Fe3O4 catalyst,the bromobenzene conversion and product yield reached about 100%and 96.3%,respectively,under a 120°C reaction temperature and 12 h reaction time.After being recycled 8 times,the conversion of bromobenzene and the recovery of the catalyst were about 90%and 93%,respectively.The nano-Pd particles were kept well dispersed in the used Pd/γ-AlOOH@Fe3O4 catalyst.     

A rotating disk electrode study of the catalytic waves produced by dismutation of O2− in the presence of superoxide dismutase

An equation is derived for the catalytic currents controlled by different dismutation processes of superoxide ion and by diffusion at a rotating disk electrode. Experimental data confirming the theoretical conclusions are presented for Cu, Zn superoxide dismutase.     

Effect of the functionalizing of carbon nanotubes on the electrodeposited catalysts’ structure and catalytic properties

The structure and hydrophilic-hydrophobic properties of functionalized single-wall carbon nanotubes are studied by the standard porosimetry method. It is shown that the functionalized nanotubes have highly hydrophilic surface; at that the summary surface area measured “by octane” decreased, as a result of the functionalizing, due to the blocking of the nanotubes’ inner channels by the functional groups located at the nanotubes’ ends. The nanotubes’ capacitive properties are studied; their charging-discharging curves appeared being highly reversible, unlike those of other carbonaceous materials. Catalytic properties of the functionalized nanotubes are studied, with particular tendency toward their using as a carrier of platinum catalysts for the methanol oxidation and oxygen electroreduction reactions. When minor amounts (5–10 μg cm⁻²) of platinum or platinum-ruthenium alloy are deposited onto the nanotubes’ hydrophilic surface, uniform layer of the catalyst is formed, with specific surface area up to 150–300 m² g⁻¹; high current of the methanol oxidation or oxygen electroreduction is observed at these catalysts. When the catalyst deposit mass increased, its specific surface area decreased, as well as the specific current of the reactions occurring thereon. When the current is related to the electrochemically active unit surface, the catalytic activity is nearly the same both for different catalyst mass deposited onto the nanotubes and the same catalyst mass at different carbonaceous carriers.     

Crystal structure and properties of the Na1−x Ru2O4 phase

Sodium ruthenium(III,IV) oxide Na_1−x Ru₂O₄ was synthesized by the solid state reaction of Na₂CO₃ and RuO₂ in inert atmosphere and characterized by X-ray powder diffraction, electron diffraction, and high-resolution transmission electron microscopy. The compound crystallizes in the CaFe₂O₄-type structure (space group Pnma, Z = 4, a = 9.2641(7) Å, b = 2.8249(3) Å, c = 11.1496(7) Å). Double rutile-like chains of the RuO₆ octahedra form a three-dimensional framework, whose tunnels contain sodium cations. The structure contains two crystallographically independent sites of ruthenium atoms randomly occupied by the Ru^III and Ru^IV cations. The superstructure with the doubled b parameter found for one of the samples under study using electron diffraction is caused, probably, by ordering of the Ru cations in the rutile-like chains. The Na_{1− x} Ru₂O₄ compound exhibits temperature-independent paramagnetism with χ₀ = 1.9·10⁻⁴ cm³ (mole of Ru⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1655–1660, October, 2006.     

EPR and DFT study of the ethylene reaction with O− radicals on the surface of nanocrystalline MgO

Research on Chemical Intermediates - Different radical forms of oxygen (O?, O 2 ? and O 3 ? ) on the surface of nanocrystalline MgO are well known. It was earlier demonstrated...     

The electronic structure of Bi2−xGdxRu2O7 and RuO2: A study by electron spectroscopy

The bismuth gadolinium pyrochlore ruthenates Bi_2−xGd_xRu₂O₇ have been studied in relation to RuO₂ by the techniques of X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) and high-resolution electron-energy-loss spectroscopy (HREELS). The composition-dependent metal-to-semiconductor transition in the pyrochlore system is mirrored by the progressive decrease with composition parameter in (i) the density of electronic states at the Fermi energy in UPS, (ii) the plasmon frequency in HREELS, and (iii) the probability of screening a Ru : 3d core hole in XPS. These changes are too gradual in themselves to pinpoint the transition, but are generally consistent with transport and X-ray diffraction data that indicate a metal-to-nonmetal transition at x = 1.55 mediated by an interplay between disorder and correlation-induced electron localization. Comparison of the results for the pyrochlores with those from RuO₂ suggest that the fine structure in the Ru : 3d spectrum of the latter material, previously believed to arise from differing oxidation states at the surface, should in fact be attributed to final-state screening effects in a stoichiometric material. Our conclusion is confirmed by the signals associated with Ru : 4d electrons in XPS, UPS, and HREELS: each of these three techniques appears to probe a conduction-electron concentration essentially equal to its bulk value. In particular, UPS confirms details of the band structure of RuO₂ not obvious from previous photoemission experiments.     

Effect of copper source on the structure–activity of CuAl2O4 spinel catalysts for CO hydrogenation

Due to the complexity of the structure–activity relationship of the CuAl₂O₄ spinel catalyst, optimization of the catalyst structure is a great challenge. In this paper, three different CuAl₂O₄ spinel catalysts were prepared by the solid-phase method using copper hydroxide, copper nitrate, and copper oxide as the copper source, respectively, to study the difference in the structure of CuAl₂O₄ spinel catalysts induced by the raw materials and the catalytic behavior for CO hydrogenation. The structure of CuAl₂O₄ spinel catalyst was characterized by XRD, BET, SEM, TEM, H₂-TPR and XPS. The activity of CO hydrogenation over the CuAl₂O₄ spinel catalyst without pre-reduction was evaluated in the slurry reactor. The results demonstrated that different copper sources had obvious influence on the CuAl₂O₄ spinel texture properties, surface enrichment degree, as well as decomposition and reduction ability, which further regulated the ratio of Cu⁺/Cu⁰ and thus affected the catalytic performance, especially the alcohol distribution. The CuAl₂O₄ spinel, employing copper hydroxide as the copper source, showed better selectivity of C₂₊OH, which was assigned to a higher ratio of Cu⁺/Cu⁰, along with larger pore size and pore volume. Moreover, the synergistic effect between Cu⁰ and γ-Al₂O₃ improved the selectivity of dimethyl ether.     

A new type of combustion tube for carbon-hydrogen determination by the “rapid combustion method”

Summary Using the empty tube technique based on earlier work ofIngram, a new type of combustion tube has been designed. The horizontal combustion tube is maintained. Halogen and sulphur oxides are absorbed by electrolytic silver wool.The nitrogen oxides are absorbed by manganese dioxide in a slightly modified absorber.

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Zusammenfassung Ein neues, horizontales Verbrennungsrohr für die Methode mit leerem Rohr nachIngram wird vorgeschlagen. Schwefeloxyde und Halogene werden an elektrolytischer Silberwolle absorbiert. Der mit Mangandioxyd gefüllte Absorptionsapparat für Stickstoffoxyde wurde etwas abgeändert.

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Résumé Utilisant la technique du « tube vide » d'après le travail antérieur deIngram, l'auteur à mis au point un nouveau type de tube à combustion. Le tube à combustion horizontal est conservé. Les halogènes et les oxydes du soufre sont absorbés par de la laine d'argent « électrolytique ». Les oxydes de l'azote sont absorbés par du bioxyde de manganèse dans un absorbeur légèrement modifiée.

     

Effects of NH 4 + and Cl− on the preparation of nanocrystalline TiO2 by hydrothermal method

Nanocrystalline TiO₂ powders with different morphologies and grain sizes were successfully synthesized by the hydrothermal method. Different concentrations of hydrochloric acid (HCl), ammonium chloride (NH₄Cl), ammonium sulfate [(NH₄)₂SO₄], and ammonium carbonate [(NH₄)₂CO₃] were used as additives in the hydrothermal process to investigate the effect of the concentration of ammonium (NH ₄ ⁺ ) and chloride ions (Cl^?) on the phase compositions, morphologies, and grain sizes of the prepared TiO₂. The as-synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy, Brunauer–Emmett–Teller analysis, and UV–Vis spectra. XRD results show that the as-synthesized powders are composed of anatase or a mixture of anatase and brookite. The grain size of the synthesized nano-TiO₂ powder ranged from 5.0 to 11.3 nm, and the related BET specific surface area varied from 127.5 to 191.0 m²/g. The photocatalytic activities of the prepared TiO₂ powders were evaluated by degradation of methylene blue (MB) in aqueous solution under UV light irradiation, and the results show that the photocatalytic performance of TiO₂ powders synthesized with additives is improved compared with that of TiO₂ prepared without any additives.     

Multicomponent QM study on the reaction of HOSO + NO2 with H2O: Nuclear quantum effect on structure and reaction energy profile

The hydrogen transfer reaction in the reaction of HOSO + NO₂ with and without H₂O have been investigated using multicomponent quantum-mechanics method, which can directly take nuclear quantum effect (NQE) of light nuclei into account. For the case of the reaction without H₂O, our calculation reveals that the reaction leading to trans-HONO is preferred. For the reaction with H₂O, water-non-mediated and water-mediated (hydrogen-relay) hydrogen transfer mechanism are investigated. The NQE of hydrogen nucleus lowers the relative energy of the stationary point structures and reduces the activation barrier of the reactions. The largest stabilization is found in the transition state structure of the hydrogen-relay type reaction. H/D isotope effects for the reactions are also analyzed. In particular, H/D isotope effect on the activation barrier is analyzed in detail with the aid of the active strain model.     

An investigation of the catalytic performance of Fe–Mn/Al2O3 nanocatalyst for light olefins production using RSM method and kinetic study

The Fe–Mn/Al₂O₃ nanocatalysts were manufactured via the sol-gel procedure and were evaluated for Fischer–Tropsch synthesis. The impact of different operational parameters of T, P, and H₂/CO ratio on the catalytic performance for light olefins production has been studied using response surface methodology (RSM). Furthermore, the optimization and modeling of selected responses were also carried out via RSM and historical data design type of DOE; and the best process conditions were found to be T = 365°C, H₂/CO = 1.50, and P = 1.50 bar. The mechanism of CO hydrogenation reaction over the Fe–Mn/Al₂O₃ nanocatalysts was also investigated using the non-linear regression method. It was found that the mechanism of the CO hydrogenation reaction is based on the Eley–Rideal type and the best-fitted equation for this mechanism was found to be −r_CO = KP_COP_H2/1+αP_CO. The obtained value of activation energy (85.20 kJ mol⁻¹) affirmed the absence of internal mass transfer limitations. The physico-chemical properties of the samples were investigated by various techniques of XRD, BET, TPR, TGA, and DSC.     

Lack of salt effect on the kinetics of the reaction SO2−4 + H3O+ → HSO−4 + H2O

It is found that the broadening of the 1100-cm⁻¹ line of SO⁻²₄, caused by increasing [H₃O⁺], is unaffected by addition of 4 M LiCl, NaBr, KCl and NH₄Cl. This finding is in line with the lack of influence of NaCl reported earlier. The significance of these findings, in terms of the reaction mechanism, is discussed.     

DTA-TG and XRD study on the reaction between ZrOCl2·8H2O and (NH4)2HPO4 for synthesis of ZrP2O7

In this paper, we report results of thermoanalytical investigation on the reaction between ZrOCl₂·8H₂O and (NH₄)₂HPO₄ in molar ratio 1:2. Differential thermal-thermogravimetric and X-ray diffraction analyses were performed in order to reveal the chemical transformations, which took place during heating of the individual compounds ZrOCl₂·8H₂O, (NH₄)₂HPO₄ and the mixture ZrOCl₂·8H₂O:2(NH₄)₂HPO₄. It was shown that the transformations in the mixture below 160 °C were connected with dehydration of ZrOCl₂·8H₂O and interaction between the components of the mixture, which resulted in the formation of NH₄Cl, NH₄H₂PO₄ and a mainly amorphous zirconium phase, most likely t-ZrO₂. The zirconium component subsequently reacted with ammonium dihydrophosphate (below 200 °C) or with dehydrated phosphate derivatives (above 200 °C), which in both cases yielded an amorphous product. The interaction between the components of the mixture resulting in the formation of ZrP₂O₇ was completed by its crystallisation at 610 °C. Our study indicates an alternative low-temperature approach for the synthesis of the technologically important ZrP₂O₇ material.     

Effect of preparation method on structural characteristics and propane steam reforming performance of Ni–Al2O3 catalysts

Propane steam reforming was studied over Ni–Al₂O₃ catalysts that were prepared by a conventional impregnation (IM) method and a one-step sol–gel (SG) technique. Both Ni–Al₂O₃ catalysts showed similar initial activity. However, IM-Ni–Al₂O₃ deactivated severely with time-on-stream of propane steam reforming. The catalyst prepared using a SG technique demonstrated stable catalytic performance. The two catalysts also showed major differences in product distribution, with SG catalyst giving much higher yields of hydrogen. Catalysts were characterized with temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), temperature-programmed oxidation (TPO), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. It was revealed that, with sol–gel preparation, highly dispersed small Ni crystallites are formed with a strong interaction with the support. This is shown to be important for coke suppression and catalyst stability.     

A computational study on the gas phase reaction of Os^＋ with N2O

The reaction of Os~+(~6D,~4F) with N_2O has been investigated at B3LYP/TZVP and CCSD(T)/6-311+G~* levels of theory.The mechanisms corresponding to O-atom and N-atom transfer reactions have been revealed.It was found that on the sextet reaction surface both the O-atom and N-atom transfer reactions undergo through direct-abstraction mechanism,leading to the formation of OsO~+ and OsN~+,whereas on quartet surface the two reactions undergo through O-N bond or N-N bond insertion mechanism.The calculated energ...