Photodecomposition of water with methane over titanium oxide photocatalysts modified with metal

Metal-loaded titanium oxide photocatalysts produced hydrogen in the photodecomposition of water vapor with methane in the flow reactor. Ag/TiO₂ has the highest activity in comparison with other metal-loaded catalysts. The experiment in the absence of methane indicated that methane could effectively function as a reducing reagent of water. The significant decrease in the hydrogen formation rate with the time on stream was observed under all reaction conditions. The recalcination and the hydrogen rereduction of the used catalyst led to the restoration of the activity of the hydrogen formation. The adsorption of products and/or reactants on the catalyst surface seemed to cause these deactivations of the hydrogen formation.     

Reaction of methoxy radicals with oxygen. I. Using dimethyl peroxide as a thermal source of methoxy radicals

Using dimethyl peroxide as a thermal source of methoxy radicals overthe temperature range of 110–160°C, and the combination of methoxy radicals and nitrogen dioxide as a reference reaction: a value was determined of the rate constant for the reaction of methoxy radicals with oxygen: is independent of nitrogen dioxide or oxygen concentration and added inert gas (carbon tetrafluoride). No heterogeneous effects were detected. The value of k₄ is given by the expression In terms of atmospheric chemistry, this corresponds to a value of 10^5.6 M^?1·sec^?1 at 298 K. Extrapolation to temperatures where the combustion of organic compounds has been studied (813 K) produces a value of 10^7.7 M^?1·sec^?1 for k₄. Under these conditions, reaction (4) competes with hydrogen abstraction or disproportionation reactions of the methoxy radical and its decomposition (3): In particular k₃ is in the falloff region under these conditions. It is concluded that reaction (4) takes place as the result of a bimolecular collision process rather than via the formation of a cyclic complex.     

Effects of discharge mode and gas composition for plasma-hydrophilized titanium surface on hydrophilic sustainability

Plasma hydrophilization under various conditions was carried out on Ti substrates to investigate the effect of the applied parameters on the hydrophilic sustainability. The plasma was discharged from gases comprising Ar and/or O₂ at various ratios using DC and RF modes. Notable differences in the surface morphology by the plasma conditions was hardly found, while the ratio of hydroxide on the surface was influenced by the discharge mode. The hydrophilicity was significantly improved regardless of the treatment conditions, that is, the gas composition and discharge mode. The deterioration of the hydrophilicity was occurred by storing in the ambient atmosphere or distilled water, wherein the deterioration in distilled water was suppressed when using DC as a discharge mode. The hydrophilicity was preserved when the specimens was stored in a physiological solution such as phosphate buffered saline solution due to the adsorption of Na⁺ and Cl⁻ in the solution; its effect was far superior to that contributed by the parameter settings. In conclusion, plasma discharge mode enabled to improve the deterioration of hydrophilicity only slightly.     

Reactions of peroxide radicals with the surface of heterogeneous catalysts in homolytic and heterolytic processes

An interrelation between homolytic and heterolytic stages is found for olefin epoxidation by hydroperoxides and cumene hydroperoxide decomposition in the presence of a heterogeneous catalyst (molybdenum selenide). Peroxide radicals that are formed in homolytic decomposition of the hydroperoxide interact with the catalyst surface. As a result, molybdenum atoms are oxidized to the highest valence state, and new reaction sites are created, on which heterolytic reactions occur. It is shown that olefin, as an electron donor, decreases the catalyst activity in the heterolytic reactions. The limited value for the olefin epoxidation rate, which is independent of the amount of the catalyst used, is explained by the disappearance of active sites on the catalyst surface due to their interaction with the neighboring sites containing adsorbed olefin molecules.     

Reaction of nitrous oxide with methane to synthesis gas: A thermodynamic and catalytic study

The aim of the present study is to explore the coherence of thermodynamic equilibrium predictions with the actual catalytic reaction of CH4 with N_2O,particularly at higher CH4 conversions.For this purpose,key process variables,such as temperature(300℃-550℃) and a molar feed ratio(N_2O/CH4 = 1,3,and 5),were altered to establish the conditions for maximized H_2 yield.The experimental study was conducted over the Co-ZSM-5 catalyst in a fixed bed tubular reactor and then compared with the thermodynamic equilibrium compositions,where the equilibrium composition was calculated via total Gibbs free energy minimization method.The results suggest that molar feed ratio plays an important role in the overall reaction products distribution.Generally for N_2O conversions,and irrespective of N_2O/CH_4 feed ratio,the thermodynamic predictions coincide with experimental data obtained at approximately 475℃-550℃,indicating that the reactions are kinetically limited at lower range of temperatures.For example,theoretical calculations show that the H2 yield is zero in presence of excess N2O(N_2O/CH_4 = 5).However over a Co-ZSM-5 catalyst,and with a same molar feed ratio(N_2O/CH_4) of 5,the H_2 yield is initially 10%at 425℃,while above450℃ it drops to zero.Furthermore,H_2 yield steadily increases with temperature and with the level of CH4 conversion for reactions limited by N_2O concentration in a reactant feed.The maximum attainable(from thermodynamic calculations and at a feed ratio of N_2O/CH4=3) H_2 yield at 550℃ is 38%,whereas at same temperature and over Co-ZSM-5,the experimentally observed yield is about 19%.Carbon deposition on Co-ZSM-5 at lower temperatures and CH4 conversion(less than 50%) was also observed.At higher temperatures and levels of CH_4 conversion(above 90%),the deposited carbon is suggested to react with N_2O to form CO_2.     

The effect of annealing on the composition and morphology of the surface of Ni-containing oxide layers on titanium formed by plasma-electrolytic method

The effect of annealing temperature on the elemental composition and morphology of the Ni-containing coatings formed by plasma-electrolytic oxidation in sodium silicate electrolyte suspension with and without sodium oleate was studied in the range 750?C850°C.     

Effects of surface chemical composition on the early growth stages of alpha-sexithienyl films on silicon oxide substrates

In organic field effect transistors, charge transport is confined to a narrow region next to the organic/dielectric interface. It is thus extremely important to determine the morphology and the molecular arrangement of the organic films at their early growth stages. On a substrate of technological interest, such as thermally grown silicon oxide, it has been recently found that alpha-sexithienyl aggregates made of flat-lying molecules can simultaneously nucleate besides islands made of molecules standing vertical. In this paper, we investigate the effects due to variations in surface chemical composition on alpha-sexithienyl ultrathin film formation. Flat-lying molecules are no longer detected when Si-OH groups present at the surface are chemically removed but also when the Si-OH or Si-H group density is maximized. This gives evidence that variations in the surface chemical composition can largely affect the nucleation and growth processes of organic/dielectric interfaces. We hypothesize that isolated OH groups can interact with alpha-sexithienyl molecules and anchor them down flat with respect to the surface.     

Reaction of methyl acrylate with titanium tetrachloride during the condensation of the vapors on a cold surface

Complex formation between methyl acrylate and titanium tetrachloride during the condensation of the vapors of the reactants on a copper surface cooled to liquid-nitrogen temperature has been studied by IR spectroscopy. It has been established that the mole fraction of reactants entering into reaction depends on the rate of deposition and has an extremal nature. A formal kinetic model is proposed which represents the relationship obtained in the study between the substances participating in complex formation and the rate of condensation of the mixture.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22. No. 6, pp. 673–679, November–December, 1986.     

Reaction of nitroxyl radicals with dichlorocarbene

Conclusions The reaction of aromatic nitroxyl radicals with dichlorocarbene, generated under phase transfer catalysis conditions, leads to the corresponding hydrazine derivatives through the abstraction of the oxygen atom from the nitroxyl radicals and formation of aminyl radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 470–472, February, 1989.     

Reaction of methyl radicals with haloalkanes

The kinetics of reactions involving halogen atom abstraction from haloalkanes by methyl radicals have been studied in the gas phase. Arrhenius parameters for halogen atom transfer were determined relative to those for methyl radical combination:

Reaction of t-butoxy radicals with norbornadiene

95 percent of the reaction of t-butoxy radical with norbornadiene occurs by radical addition followed by rearrangement to nortricyclyl and 7-t-butoxynorbornenyl products; the remainder includes a novel radical rearrangement involving a 1,3-H shift and some radical abstraction observed for the first time.     

Analysis of buoyancy assisting and opposing flows of colloidal mixture of titanium oxide,silver, and aluminium oxide nanoparticles with water due to exponentially stretchable surface

Energy is essential for a nation's economic growth. Energy is recognized in contemporary society as being crucial to the development of quality of life and sustainability. The environment transforms/absorbs heat and sunlight in a variety of ways. Some of these transitions lead to the flow of renewable energy sources like wind and biomass. Solar energy has become one of the promising alternative energy sources in the future because to the improvements made to enhance its performance. In this context, the impact of solar radiation on modified nanofluid flow over an exponential stretching sheet is examined. Using the proper similarity transformations, the governing equations for the flow assumptions are reduced to ordinary differential equations. The numerical simulation of these simplified equations is then performed using the Runge-Kutta Fehlberg method and the shooting methodology. With the aid of graphs and tables, the effects of numerous parameters on the involved fields are described. Results reveal that the modified nano liquid shows increased heat transport for opposing flow situation than the assisting flow situation for incremented values of porosity parameter and volume fraction. The modified nanoliquid shows increased heat transport for opposing flow situation with respect to augmented values of radiation parameter.     

Reaction of amino radicals with olefins: Theoretical aspects

The role of photocatalysts in improving the photochemical synthesis of fatty amines has been examined. Ab initio SCF and CI calculations for the addition of the aminyl radical NH₂^• to ethylene are reported. In contrast with previous theoretical results a low activation energy and a rather small exothermicity were determined. Thus an explanation for the known inactivity of amino radicals in addition reactions can be found in the possibility of a retroaddition. The calculations indicate that the role of photocatalysts could be explained by a significant stabilization of the addition photoproduct blocking the reversibility of the process. The involvement of the photocatalyst with the primary photoproduct NH₂^• should also be considered in view of a significant increase in the exothermicity observed.