The parameters of hydrogen chloride and hydrogen bromide direct-current glow-discharge plasmas

A comparative analysis of the parameters of HCl and HBr plasmas was performed by means of mathematical simulation, solving the Boltzmann kinetic equation in the one-component approximation. The specifics of the kinetics of the electron impact-induced processes and the composition of plasma charged species were analyzed.     

Behavior and surface energies of polybenzoxazines formed by polymerization with argon,oxygen, and hydrogen plasmas

Polybenzoxazine (PBZZ) thin films can be fabricated by the plasma‐polymerization technique with, as the energy source, plasmas of argon, oxygen, or hydrogen atoms and ions. When benzoxazine (BZZ) films are polymerized through the use of high‐energy argon atoms, electronegative oxygen atoms, or excited hydrogen atoms, the PBZZ films that form possess different properties and morphologies in their surfaces. High‐energy argon atoms provide a thermodynamic factor to initiate the ring‐opening polymerization of BZZ and result in the polymer surface having a grid‐like structure. The ring‐opening polymerization of the BZZ film that is initiated by cationic species such as oxygen atoms in plasma, is propagated around nodule structures to form the PBZZ. The excited hydrogen atom plasma initiates both polymerization and decomposition reactions simultaneously in the BZZ film and results in the formation of a porous structure on the PBZZ surface. We evaluated the surface energies of the PBZZ films polymerized by the action of these three plasmas by measuring the contact angles of diiodomethane and water droplets. The surface roughness of the films range from 0.5 to 26 nm, depending on the type of carrier gas and the plasma‐polymerization time. By estimating changes in thickness, we found that the PBZZ film synthesized by the oxygen plasma‐polymerization process undergoes the slowest rate of etching in CF₄ plasma. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4063–4074, 2004     

Radio-frequency induction plasmas at atmospheric pressure: Mixtures of hydrogen,nitrogen, and oxygen with argon

Numerical calculations are reported which simulate atmospheric-pressure radiofrequency induction plasmas consisting of either pure argon or mixtures of argon with hydrogen, nitrogen, or oxygen. These calculations are compared to observations of laboratory plasmas generated with the same geometry and run conditions. The major features of the laboratory plasmas are predicted well by the calculations: the pure argon plasma is the largest, with the argon-oxygen plasma slightly smaller. The argon-nitrogen plasma is considerably smaller and the argon-hydrogen plasma is the shortest, although somewhat fatter than the argon-nitrogen case. The calculations are not entirely successful in predicting the exact location of the plasmas relative to the coils. A likely explanation is that there is significant uncertainty regarding the actual power coupled to the laboratory plasmas.     

Transport coefficients of argon,nitrogen, oxygen,argon-nitrogen,and argon-oxygen plasmas

Calculated values of the viscosity, thermal conductivity, and electrical conductivity of argon, nitrogen, and oxygen plasmas, and mixtures of argon anti nitrogen and of argon anti oxygen, are presented. In addition, combined ordinary, pressure, and thermal diffusion coefficients are given for the gas mixtures. These three combined diffusion coefficients fully describe di fusion of the two gases, irrespective of their degree of dissociation or ionizati on. The calculations, which assume local thermodynamic equilibrium, are performed! for atmospheric-pressure plasmas in the temperature range /torn 300 to 30,000 K. A number of the collision integrals used in calculating the transport coefficients are significantly more accurate than values used in previous theoretical studies, resulting in more reliable values of the transport coefficients. The results are compared with those of published theoretical and experimental studies.     

The dehydrogenation of cyclohexane on an AP-64 industrial platinum catalyst subjected to plasma chemical treatments

The influence of glow discharge plasma in oxygen and argon and high-frequency discharge plasma in hydrogen on the activity of the AP-64 (Pt/γ-Al₂O₃) catalyst in the dehydrogenation of cyclohexane was studied. The catalytic experiments were performed in a flow unit and under static conditions in a vacuum. Under flow conditions, catalyst treatment with plasmas in O₂ and Ar decreased the yield of benzene by ～50% but strengthened temperature hysteresis because of the formation of active carbon on the surface of the catalyst. Under static conditions, argon plasma and high-frequency discharge H₂ plasma multiply increased the rate of the reaction because of an increase in the number of active centers, whereas an oxygen plasma decreased the rate of the reaction by two times because of an increase in activation energy. The determination of the order of the reaction led us to suggest that the stage scheme of the reaction did not change after plasma chemical catalyst treatments.     

Cathode erosion on copper electrodes in steam,hydrogen, and oxygen plasmas

Experimental data are presented for cathode erosion rates on copper cathodes (or magnetically rotated arcs in steam, and mixtures of steam, hydrogen, and oxygen with argon. Measurements were also made of the arc voltage and velocity. The erosion rates for steam and oxygen plasmas were significantly lower than those .16r argon and hydrogen. Pure steam and 10% oxygen in argon gave erosion rates of 2.3 and 6.1 g/ C respectively while pure argon and 70% hydrogen in argon gave rates of 14.8 and 13.0 g/C respectively. Erosion rates decreased with increasing are velocities. The variation of arc velocity with operating conditions is described in terms of both aerodynamic and surface drag on the arc and arc root respectively.     

The use of plasmas in catalysis: catalyst preparation and hydrogen production

Plasma technologies are introduced in the field of hydrogen production related to fuel cells. Two ways are described: Plasma synthesis of catalysts and membranes for the production and purification of hydrogen and, direct production of hydrogen based on atmospheric plasma-assisted methane steam reforming.     

Adsorption of isopropanol on a nickel catalyst

The adsorption isotherms of isopropanol on a Ni catalyst (15 wt % on SiO₂) in the temperature range of 273–303 K are determined. An increase in the isosteric heat of adsorption and entropy of adsorption after treating the catalyst with high frequency plasma in hydrogen and adding 1.5 wt % of Ce is detected, with treatment involving glow discharge plasma in Ar and O₂ having virtually no impact on these values. At a low degree of surface filling, the adsorption isotherms are described by the equation of induced adsorption. It is concluded that adsorbed isopropanol molecules are present in two forms: positively and negatively charged.     

Dehydrogenation of isopropanol on a cerium-nickel catalyst

The effect of a cerium additive on the catalytic activity of a 2 wt % Ni/SiO₂ catalyst is studied. It found that under both flow and static conditions the activity of (2 wt % Ni + 0.2 wt % Ce)/SiO₂ catalyst is higher than that of the original sample; the increase in activity results from a sharp increase in the number of active sites. A change in the composition of the surface layer of the catalysts is analyzed by X-ray photoelectron spectroscopy. It was found that the fraction of nickel decreases and the fraction of carbon increases in cerium-containing catalyst. An explanation of the change in the elemental composition of the catalytic active sites of a nickel catalyst in the presence of cerium is proposed on the basis of XPS data and previous quantum chemical calculations.     

Dehydrogenation of isopropanol on a modified copper catalyst

The influence of plasmochemical treatments of the 5 wt % Cu/SiO₂ catalyst and cerium additives on the activity of the catalyst in isopropanol dehydrogenation was studied. After the catalyst was treated with high-frequency plasma in H₂ under the flow conditions, the conversion of alcohol increased. The reaction kinetics was studied under static conditions. The rate constant increased 1430-fold after the introduction of an optimum dose of Ce and treatment in Ar, O₂, and H₂ plasma and 550-fold after treatment with high-frequency plasma in H₂. The experimental activation energy increased in all instances; the activity grew because of the increase in the number of active centers. The promoting action of cerium was explained by the positive charge of the Ce^+α adatom, which initiated growth of the surface electron density; the influence of plasmochemical treatments was explained by the change in the number of structural defects and their character. Possible stepwise reaction schemes were considered based on ab initio quantum-chemical calculations.     

Effects of plasmochemical treatments and cerium additions on the structural characteristics and activity of copper catalyst particles in isopropanol dehydrogenation

The effect of the treatment of the 5 wt % Cu/SiO₂ (I) and (5 wt % Cu + 0.5 wt % Ce)/SiO₂ (II) catalysts with glow discharge plasma in O₂, H₂, and Ar on their structural characteristics was studied by X-ray phase analysis; the influence of cerium additions and plasmochemical treatments on the catalyst activity in isopropanol dehydrogenation was also investigated. Under the plasmochemical treatment, the diameters of Cu particles in catalyst I nearly doubled and microstresses in the metal particles also changed. Catalyst II was X-ray amorphous both before and after plasmochemical treatments. The activity of I after plasmochemical treatment increased because of the increase in the number of centers and changes in their composition. Growth of the activity of I compared with the activity of II was explained by the formation of new catalytic centers due to positive charging of the Ce^+?? adatom on the surface of the copper particle.     

The kinetics of the dehydrogenation of cyclohexanol to cyclohexanone on a modified copper-magnesium catalyst

Conclusions Studies on the dehydrogenation of cyclohexanol to cyclohexanone on a copper-magnesium catalyst have shown that modification of the catalyst through the introduction of calcium has no effect on the reaction kinetics.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 519–521, March, 1981.     

Effect of the treatment of chromic oxide with hydrogen and oxygen on its catalytic activity in dehydrogenation and dehydration reactions

Summary We determined the activation energies of the dehydrogenation of cyclohexane and the dehydrogenation and dehydration of isopropyl alcohol on chromic oxide that had been subjected to various preliminary treatments, namely, with hydrogen and air separately and a combination of the two. From these data we found the energies of the bonds of hydrogen, carbon, and oxygen with the surface of chromic oxide. Information was obtained on the comparative sizes of the catalytically active surfaces of the catalyst.