Isotope effect of H2/D2 and H2O/D2O for the PROX reaction of CO on the FeOx/Pt/TiO2 catalyst

The oxidation reaction of CO with O₂ on the FeOx/Pt/TiO₂ catalyst is markedly enhanced by H₂ and/or H₂O, but no such enhancement occurs on the Pt/TiO₂ catalyst. Isotope effects were studied by H₂/D₂ and H₂O/D₂O on the FeOx/Pt/TiO₂ catalyst, and almost the same magnitude of isotope effect of ca. 1.4 was observed for the enhancement of the CO conversion by H₂/D₂ as well as by H₂O/D₂O at 60 °C. This result suggests that the oxidation of CO with O₂ via such intermediates as formate or bicarbonate in the presence of H₂O, in which H₂O or D₂O acts as a molecular catalyst to promote the oxidation of CO as described below.      

Continuous and scale‐up synthesis of high purity H2O2 by safe gas‐phase H2/O2 plasma reaction

A new generation of double dielectric barrier discharge (DDBD) reactor featured by a metal powder (MP) high voltage electrode is presented. The MP high voltage electrode not only has excellent homogeneous discharge performance but also has the advantage of without regular maintenance. Therefore, the MP‐DDBD reactor was proved to be suitable for the uninterrupted and safe synthesis of high purity H₂O₂ aqueous solution with up to 65 wt % concentration from the H₂/O₂ mixture. The scale‐up synthesis of H₂O₂ was successfully attempted in an integrated device based on the MP‐DDBD reactor. The future practical H₂O₂ synthesizer based on the MP‐DDBD reactor will be small and movable, and therefore, be convenient to supply high purity H₂O₂ on site for small scale users like semiconductor industry. © 2013 American Institute of Chemical Engineers AIChE J 60: 415–419, 2014     

NO + H2 reaction on Pd/Al2O3 under lean conditions: kinetic study

This paper deals with the kinetics of the NO + H₂ + O₂ reactions on Pd/γ-Al₂O₃. Steady state rate measurements have been discussed in the light of previous mechanism proposals involving a dissociation step of molecular NO adsorbed species on Pd. In the absence of oxygen, the dissociation of NO_ads species is assisted by chemisorbed H atoms. However, different kinetic features have been observed in the presence of oxygen. Practically, the light-off curve of NO shifts towards higher temperature in the presence of O₂. In addition the H₂ + O₂ reaction extensively occurs in the temperature range of this study. Such tendencies have been explained by changes in the adsorptive properties of noble metals and also in the nature of elementary steps for the dissociation of NO. In the presence of a large extent of O₂, hydrogen coverage would sharply drop and would not further assist the dissociation of NO as in the absence of O₂.     

废水阴离子化学组分对O3/H2O2降解TNT功效的影响

结合实际三硝基甲苯(TNT)废水的水质状况,选择HCO3-、NO3、HCOO、MnO4、SO42-及C1-等为代表性污染组分,以TNT去除率及反应速率常数为评价指标,开展了阴离子对O3/H2O2降解TNT功效影响的实验研究.结果表明,废水中阴离子对O3/H2O2降解TNT功效的影响,与离子种类及浓度的关系密切,HCO3-、HCOO、MnO4-等对O3/H2O2降解TNT具有抑制作用,且随浓度的增加而加强,抑制作用能力HCOO＞HCO3-＞MnO4-,而NO3、SO42-及Cl-等对O3/H2O2降解TNT作用功效几乎没有影响HCOO-、HCO3-可能影响O3/H2O2体系中·OH的形成,MnO4-既影响·OH的形成又影响其寿命,使O3/H2O2降解TNT的功效降低.     

Fabrication of porous silicon nanowires by MACE method in HF/H2O2/AgNO3 system at room temperature

In this paper, the moderately and lightly doped porous silicon nanowires (PSiNWs) were fabricated by the ‘one-pot procedure’ metal-assisted chemical etching (MACE) method in the HF/H₂O₂/AgNO₃ system at room temperature. The effects of H₂O₂ concentration on the nanostructure of silicon nanowires (SiNWs) were investigated. The experimental results indicate that porous structure can be introduced by the addition of H₂O₂ and the pore structure could be controlled by adjusting the concentration of H₂O₂. The H₂O₂ species replaces Ag⁺ as the oxidant and the Ag nanoparticles work as catalyst during the etching. And the concentration of H₂O₂ influences the nucleation and motility of Ag particles, which leads to formation of different porous structure within the nanowires. A mechanism based on the lateral etching which is catalyzed by Ag particles under the motivation by H₂O₂ reduction is proposed to explain the PSiNWs formation.     

31-P NMR study study of acidic sites on Al2O3 and Al2O3-SnO2 after reaction with CCl2F2/H2

The surface acidic properties of two series of samples,-Al₂O₃ and-Al₂O₃-SnO₂ after reaction with CCl₂F₂/H₂ (CFC12/H₂), have been investigated by solid state high resolution CP/MAS 31-PNMR, using trimethylphosphine (TMP) as a probe molecule. It was found after reaction, that Brønsted acid sites were formed on the-Al₂O₃ surface. The longer the reaction time, the more rigidly TMP bonded to the acid sites. For the-Al₂O₃-SnO₂ system, Brønsted acid sites were also found on both the Al₂O₃ and SnO₂ surfaces after reaction of the-Al₂O₃-SnO₂ system with CFC12/H₂. The signal intensity relevant to these sites, indicates that the SnO₂ component is attached to, and therefore covers Brønsted sites of-Al₂O₃. Two types of Lewis acid site initially present on SnO₂ were not observed after reaction with CFC12/H₂.     

Characterization of the dynamic oxygen migration over Pt/CeO2-ZrO2 catalysts by O/O isotopic exchange reaction

To characterize the oxygen mobility over metal supported catalysts on a dynamic and in situ base, ¹⁸O/¹⁶O isotopic exchange reaction combined with CO oxidation was designed and exemplified on three kinds of three way catalysts of Pt/CeO₂-ZrO₂ (CZ-O, CZ-D and CZ-R). The obtained oxygen diffusion coefficients, oxygen release rate, and oxygen storage capacity were discussed and correlated with XRD spectra and other physical parameters. It was found that the oxygen mobility and oxygen storage capacity were parallel to the structural homogeneity of Zr introduction into the CeO₂ frame work, and decreased as: CZ-R > CZ-D > CZ-O. These results indicated that this combined isotopic exchange technique could be used to quantify the surface and bulk oxygen mobility, the oxygen storage capacity and oxygen release rate over the metal supported catalysts, and could be employed as a meaningful probe into the nature of CeO₂-ZrO₂ oxygen storage material. The oxygen mobility is also another important indicator for the development of oxygen storage materials.     

The issue of selectivity in the direct synthesis of H2O2 from H2 and O2: the role of the catalyst in relation to the kinetics of reaction

The kinetic behavior in the direct synthesis of H₂O₂ with Pd–Me (Me = Ag, Pt) catalysts prepared by depositing the noble metals by electroless plating deposition (EPD) or deposition–precipitation (DP) methods on α-Al₂O₃ asymmetric ceramic membrane with or without a further surface coating by a carbon thin layer is reported. The effect of the second metal with respect to Pd-only catalysts considerably depends on the presence of the carbon layer on the membrane support. Several factors in the preparation of these membranes as well as the reaction conditions (temperature, concentration of Br⁻, pH) determine the selectivity in H₂O₂ formation, influencing the rate of the consecutive reduction of H₂O₂ (which is faster with respect to H₂O₂ decomposition on the metal surface) and/or of direct H₂ + O₂ conversion to H₂O. Defective Pd sites are indicated to be responsible for the two unselective reactions leading to water formation (parallel and consecutive to H₂O₂ formation), but the rate constants of the two reactions are differently influenced from the catalytic membrane characteristics. Increasing the noble metal loading on the membrane not only increases the productivity to H₂O₂, but also the selectivity, due to the formation of larger, less defective, Pd particles.     

Oxidization of carbon nanotubes through hydroxyl radical induced by pulsed O2 plasma and its application for O2 reduction in electro-Fenton

The oxidation of carbon nanotubes (CNTs) by hydroxyl radical produced by pulsed O₂ plasma in a gas-liquid hybrid discharge reactor was conducted with the goal of enhancing their solubility and improving the yield of H₂O₂ in electro-Fenton. Data from the characterization experiments showed that oxygen bearing groups (COH, COO, COOH, CO) were formed on the surface of CNTs. The possible mechanism indicated that introduction of oxygen bearing groups onto CNTs could be attributed to the attacks by hydroxyl radical. The oxidized CNTs were easily dispersed in ethanol. The H₂O₂ yield on the original CNTs was 102 mg/L at −0.85 V after 90 min; in contrast, H₂O₂ yield on CNTs-15 reached 146 mg/L under the same conditions, resulting from the enhancement of the accessibility of O₂ on CNTs. In the electro-Fenton, the removal of methyl orange on the original CNTs was around 40%, and it increased to 95% on CNTs-15.     

4,4'-二(氯甲基)联苯在乙腈/水中的水解反应

4,4'-二(氯甲基)联苯在蒸馏水中受热至回流,40 h内未观察到有羟基取代苄基中氯原子的亲核取代反应发生.水中有乙腈存在,该反应就会发生,产物是4,4'-二(羟甲基)联苯.反应速度与乙腈/H2O的比例相关,当乙腈/H2O =20/1(容积比)时,完成该反应需要29 h;而当乙腈/H2O=1/50时,完成该反应需要46 h.若在乙腈/H2O介质中添加KOH,反应速度会加快,但同时会发生副反应以致生成一种淡黄色的树脂状物质.4,4'-二(氯甲基)联苯的纯度高,水解反应的产率及4,4'-二(羟甲基)联苯的纯度也高.当4,4'-二(氯甲基)联苯的纯度从98% 降低到92%时,水解反应的产率从98.6%降低到94.4%,产物4,4'-二(羟甲基)联苯纯度从99.2%下降到98.6%. 如4,4'-二(氯甲基)联苯的纯度进一步降低到85%,则反应产率急剧下降到80.9%,同时产物4,4'-二(羟甲基)联苯纯度下降到94.3%.     

On the development of metallic particles and their initial catalytic properties in the CO + H2 reaction over Co/Al2O3 catalyst

Formation of Co^o phases with different surface structure over 10 wt% Co/Al₂O₃ and their catalytic properties were induced by pretreatments in H₂ at 570 K for 1 h or 20 h. Electronic behaviour of the Co^o phase, which consists of small (after 1 h reduction) or large bulk-like particles (after 20 h reduction), did not change during the CO hydrogenation after 5 h on stream as was determined by XPS. On the basis of the measured C₂₊ hydrocarbon selectivities the CO molecules are suggested to dissociate on small Co particles to a larger extent than on large cobalt particles. The slight decrease in the catalytic activity with increasing time on stream obtained for the long-term reduced sample is explained by the change in the surface Co^o content detected by XPS. The increase in the catalytic activity along with the change in olefin selectivity, measured for the sample reduced for 1 h, is interpreted by the change of a reaction path involving the Co^o-support interface during the initial period of the reaction.     

C2H2 oxidation by plasma/TiO2 combination: Influence of the porosity, and photocatalytic mechanisms under plasma exposure

Plasma/catalyst combination is an active solution to reach high conversion rates at low energetic cost. TiO₂ is one of the catalysts frequently used in dielectric barrier discharges. Plasma/TiO₂ synergy was already exhibited but the mechanisms still have to be understood. This work distinguishes three main effects involved in the synergy: (a) effect of catalyst on the injected power, (b) the effect of porosity on C₂H₂ oxidation, and (c) the photocatalytic degradation of C₂H₂ on TiO₂ under plasma exposure. Different glass fibres-based catalytic materials coated with SiO₂ and/or TiO₂ nano-particles are used to separate these three contributions regarding to C₂H₂ conversion. It is reported that at constant voltage the injected power is mainly increased by the presence of glass fibres. C₂H₂ oxidation is mainly enhanced by the macroporosity of glass fibres and in a minor way by the nano-particles. The production of O atoms close to the surface is probably responsible for the higher C₂H₂ removal efficiency with porous material. The photocatalytic activity of TiO₂ is negligible in the plasma except if additional UV lamps are used to activate TiO₂. With external UV, photocatalytic activity is more efficient in the plasma phase than in a neutral gas phase. This plasma/photocatalysis synergy is due to the use of O atoms in photocatalytic mechanisms.     

Determination of the diffusion coefficient of an inserted species by impedance spectroscopy: application to the H/H x Nb2O5 system

Impedance spectroscopy, unlike large signal methods, allows the diffusion coefficient of an inserted species to be determined as a function of the electrode potential. The expression for the restricted linear diffusion impedance may be modified to empirically account for the difference of the electrochemical system behaviour from the ideal. It is then possible to estimate the diffusion coefficient of the inserted species from characteristic frequencies on the Nyquist diagrams and/or from the frequencies corresponding to the intersection of the asymptotes of the log (–Im Z), log f graphs. These estimations are independent of assumptions concerning the active area of the electrode. The method has been applied to the study of hydrogen insertion in H _x Nb₂O₅.     

Significant enhancement of the oxidation of CO by H2 and/or H2O on a FeO x /Pt/TiO2 catalyst

Oxidation of CO on the FeO _x /Pt/TiO₂ catalyst is markedly enhanced by H₂ and/or H₂O at 60 °C, but no such enhancement is observed on the Pt/TiO₂ catalyst, but shift reaction (CO + H₂O → H₂ + CO₂) does not occur on the FeO _x /Pt/TiO₂ catalyst at 60 °C. DRIFT-IR spectroscopy reveals that the fraction of bridge bonded CO increases while that of linearly bonded CO decreases on the FeO _x loaded Pt/TiO₂ catalyst. The in-situ DRIFT IR spectra proved that the bridged CO is more reactive than the linearly bonded CO with respect to O₂, and the reaction of the bridge-bonded CO with O₂ as well as of the linearly bonded CO is markedly enhanced by adding H₂ to a flow of CO + O₂. From these results, we deduced that the promoting effect of H₂ and/or H₂O is responsible for the preferential oxidation (PROX) reaction of CO on the FeO _x /Pt/TiO₂ catalyst, and a following new mechanism via the hydroxyl carbonyl or bicarbonate intermediate is proposed for the oxidation of CO in the presence of H₂O.      

O3/H2O2 Treatment of Methyl-terf-Butyl Ether in Contaminated Waters: Effect of Background COD on the O3-Dose

The destruction of methyl-tert-butyl ether (MTBE) in contaminated waters by O₃/H₂0₂ process was studied and the influence background COD, alkalinity, and hydrogen peroxide and MTBE concentrations on process treatment efficiency and ozone dosage was investigated. The treatment efficiency was evaluated by an Efficiency Index, which is based on electrical energy requirement for ozone production. It was found that the treatment efficiency decreases linearly with increasing concentrations of MTBE at constant background COD and with background COD at constant MTBE concentration. A simplified kinetic scheme was presented to account for these observations.     

Bimetallic catalysts as dissipative structures: stationary concentration patterns in the O2 + H2 reaction on a composite Rh(110)/Pt surface

The O₂ + H₂ reaction has been studied under low pressure conditions (10^-5 mbar) employing a microstructured Rh(110)/Pt surface as catalyst. Photoemission electron microscopy (PEEM) and scanning photoelectron microscopy (SPEM) were used as spatially resolving in situ methods. Under reaction conditions stationary concentration patterns (Turing‐like structures) of the adsorbates develop inside the Pt domains which are associated with a compositional change of the metallic substrate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of fluorine chemistry in the remote plasma enhanced chemical vapor deposition of silicon films from Si2H6-SiF4-H2

SiF₄ was added into Si₂H₆-H₂ to deposit polycrystalline silicon films at low temperatures around 400°C in a remote plasma enhanced chemical vapor deposition reactor. It was found out that the fluorine chemistry obtained from SiF₄ addition had an influence on the chemical composition, crystallinity, and silicon dangling bond density of the film. The fluorine chemistry reduced the amount of hydrogen and oxygen incorporated into the film and also suppressed the formation of powders in the gas phase, which helped the crystallization at low temperatures. Effect of SiF₄ concentration as well as the deposition temperature was also significant.     

Oxidative coupling of methane over a La2O3/CaO catalyst. Optimization of reaction conditions in a bubbling fluidized-bed reactor

Oxidative coupling of methane over a La₂O₃/CaO catalyst was investigated in laboratory-scale fluidized-bed reactors (ID = 5 and 7 cm) in the following range of reaction conditions: T = 700 – 880°C, P = 41 – 72 kPa and P = 6 – 29 kPa. The maximum C₂₊ selectivity and yield amounted to 73.8% (T = 800°C, X = 13.1%, Y = 9.7%) and 16.0% (T = 840°C, X = 34.0%, S = 47.2%), respectively. Axial gas concentration profiles revealed that C₂₊ selectivity was not only influenced by oxidative consecutive reactions, but also by steam reforming of ethylene. When diluting the catalytic bed (m_cat = 145 g) with quartz (m = 200 and 400 g), a slight decrease of the selectivity (1–2%) was observed. The dilution of the feed gas with nitrogen only led to only a small increase (< 2%) of the C₂₊ selectivity.     

Catalytic partial oxidation of CH4 over bimetallic Ni‐Re/Al2O3: Kinetic determination for application in microreactor

The activity of a novel Ni‐Re/Al₂O₃ catalyst toward partial oxidation of methane was investigated in comparison with that of a precious‐metal Rh/Al₂O₃ catalyst. Reactions involving CH₄/O₂/Ar, CH₄/H₂O/Ar, CH₄/CO₂/Ar, CO/O₂/Ar, and H₂/O₂/Ar were performed to determine the kinetic expressions based on indirect partial oxidation scheme. A mathematical model comprising of Ergun equation as well as mass and energy balances with lumped indirect partial oxidation network was applied to obtain the kinetic parameters and then used to predict the reactant and product concentrations as well as temperature profiles within a fixed‐bed microreactor. H₂ and CO production as well as H₂/CO₂ and CO/CO₂ ratios from the reaction over Ni‐Re/Al₂O₃ catalyst were higher than those over Rh/Al₂O₃ catalyst. Simulation revealed that much smoother temperature profiles along the microreactor length were obtained when using Ni‐Re/Al₂O₃ catalyst. Steep hot‐spot temperature gradients, particularly at the entrance of the reactor, were, conversely, noted when using Rh/Al₂O₃ catalyst. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1691–1701, 2018     

Inductively coupled plasma etching of Pb(ZrxTi1-x)O3 thin films in Cl2/C2F6/Ar and HBr/Ar plasmas

Pb(Zr_xTi_1-x)O₃ thin films were etched in an inductively coupled plasma by using various etch gases such as Cl₂/Ar, C₂F₆/Ar, Cl₂/C₂F₆/Ar and HBr/Ar. The etch rates and etch profiles for each etch gas were investigated. Fast etch rates were obtained in chlorine-containing etch gases (e.g., Cl₂/Ar and Cl₂/C₂F₆/Ar), and clean and steep etch profiles were achieved in Cl₂/Cv₂F₆/Ar or HBr/Ar gases. The gas mixture of Cl₂ and C₂F₆ was proposed to give a fast etch rate and a steep sidewall angle of etched patterns. The optimum gas mixture of Cl₂C₂F₆/Ar was found by varying the gas ratio of Cl₂ to C₂F₆. On the other hand, HBr/Ar gas as an alternative for etching of the Pb(Zr_xTi_1-x)O₃ films was examined. Cl₂/C₂F₆/Ar and HBr/Ar etch gases were compared with respect to etch rate, etch profile and electrical properties.