Krzysztof Schmidt-Szałowski

The properties of cobalt oxide catalyst for ammonia oxidation

Abstract A cobalt oxide catalyst for ammonia oxidation of high and stable activity and selectivity has been obtained and tested in a fluidized bed laboratory reactor. Its active component is Co 3 O 4 . It has been found that much less nitrous oxide is produced in ammonia oxidation on this catalyst than on platinum. The macrostructure of the cobalt catalysts, and especially the presence of mesopores of diameter 3 /g. A hypothetical model has been presented to explain the effect of the catalysts macrostructure on its properties.

Thin Films Deposition from Hexamethyldisiloxane and Hexamethyldisilazane under Dielectric-Barrier Discharge (DBD) Conditions

Hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDSN) were used as organosilicon reagents for PE-CVD of thin films under filamentary barrier-discharge conditions at atmospheric pressure. Efficient discharges were obtained in the region of moderate frequencies (5 kHz). The following mixtures of organosilicon reagents with carrier gas and oxidants or ammonia were investigated: HMDSO+Ar, HMDSO+N2, HMDSO+O2+Ar, HMDSO+N2O+Ar, and HMDSN+NH3+N2. Under such conditions HMDSO was converted to produce thin films (10–1000 nm) of silicon oxide, generally containing admixtures of residual “organic” content (Si—CHn and Si—H groups). The films deposited from HMDSN+NH3+N2 contained silicon, nitrogen and oxygen.

Heterogeneous Effects in the Process of Ozone Synthesis in Electrical Discharges

Catalytic effects of solid surfaces in the synthesis of ozone have been examined under semicorona discharges conditions. It was found out that in the presence of a granular dielectric (silica) in the discharge gap, the ozone formation was accelerated and higher ozone concentrations were obtained. The mechanism of catalytic effects of silica is discussed.

Methane Conversion into C2 Hydrocarbons and Carbon Black in Dielectric-barrier and Gliding Discharges

Abstract The methane conversion into C2 hydrocarbons, carbon black, and hydrogen was studied under plasma conditions at atmospheric pressure using dielectric barrier discharges (DBD) and gliding discharges. Ethane was the main product of the methane conversion under the filamentary DBD action in the mixtures CH4+Ar, thus it may be concluded that under the conditions of DBD microdischarges, the methane transformation can be terminated after one of the first steps of the chain reaction when ethane is produced. The methane conversion rate increased in the presence of dielectric granular packing (quartz glass and silica gel). Using the gliding discharges, two processes were examined: the methane conversion into unsaturated hydrocarbons C2 (mainly acetylene) and into carbon black. For these processes, it was found that the methane concentration in the starting gas mixtures (CH4+H2 and CH4+Ar) is one of the main parameters influencing the conversion rate and the unit energy consumption. The equilibrium in the CH4+H2 mixtures at the pressures of 1 and 10 bar was examined and the temperature ranges of the solid carbon stability were determined.

Carbon Tetrachloride Decomposition by Pulsed Spark Discharges in Oxidative and Nonoxidative Conditions

The estimation of pulsed-spark-discharge efficiency for destroying unwanted stable gaseous impurities is an object of the present study. A laboratory-scale reactor was developed to study the efficiency of pulsed spark discharges (PSDs) for CCl₄ decomposition under oxidative and nonoxidative conditions at atmospheric pressure. In the discharge, chlorine gas was the main product produced from CCl₄ in addition to minor amounts of additional products. These products were the following: 1) C₂Cl₄, C₂Cl₆, and solid deposits containing chlorine and carbon for the inlet CCl₄ + Ar mixture and 2) CO₂ with small amounts of COCl₂ for CCl₄ + O₂ mixture. For both diluting gases, it was possible to reach a high CCl₄ conversion (98% for CCl₄ + O₂ and 93% for CCl₄ + Ar). CCl₄ was chosen as a model substance, because of its simple chemical composition and high stability of its structure. For this reason, the positive result of experiments with CCl₄ gave evidence that using the PSD may be an effective way for the abatement of gaseous pollutant emission.

Plasma-catalytic Conversion of Methane by DBD and Gliding Discharges

Abstract The methane conversion into C2 hydrocarbons was examined at atmospheric-pressure plasmas generated by dielectric barrier discharges (DBD) and gliding discharges (GD) using different mixtures of gases (CH4 with Ar, CO2, and H2). Ethane was the main product of the methane conversion in filamentary DBD, whereas mainly acetylene was generated by gliding discharge. It was found that one of the commercial catalysts (Cu/Zn/Al2O3) can be used for the methane conversion in DBD. A new type of the gliding discharge reactor with a widening upwards working chamber, and two vertical electrodes was designed. A spouted-bed of alumina-ceramic particles (0.16 - 0.5 mm) was maintained in the inter-electrode volume by a stream of gaseous reactants passing upward. The presence of the spouted bed resulted in: 1) an increase in voltage and decrease in current, and 2) an increase of the overall methane conversion and selectivity into C2 hydrocarbons.

A comparison of carbon tetrachloride decomposition using spark and barrier discharges

Abstract The decomposition of CCl4 in air was investigated at atmospheric pressure in two discharges. Reactors used to generate electrical discharges were powered by the same electric power supply. In both reactors, nearly 90% conversion of CCl4 was obtained. All chlorine was in the form of Cl2 in the process carried out in the barrier discharge, while in the spark discharge, COCl2 was formed. The conversion of CCl4 to COCl2 ranged from 2 to 12%. NO was formed in both discharges but the NO content in the gas leaving the reactors was 1.7–2.7% for the spark discharge and 0.045–0.06% for the barrier discharge. O3 was produced only in the barrier discharge and its content ranged from 0.1 to 0.2%. Graphical Abstract

Plasma-Catalytic Processes in Gliding Discharges

Abstract Two kinds of plasma-catalytic processes initiated by gliding discharges (GD) were examined: 1) nitrous oxide decomposition and 2) methane non-oxidative coupling to C2 hydrocarbons. In the first case, the GD reactor with stationary catalyst bed was used. It was found that the selected catalysts CuO/Al2O3 and Fe2O3/ Al2O3 may increase the conversion rate of N2O into N2 and O2 in the plasma-catalytic system, not affecting, however, its oxidation to NO. For the methane coupling, a new model of GD reactor has been developed with a mobile (spouted) bed of catalyst particles. In that process, C2 hydrocarbons were the dominant reaction products, however, some amounts of non-volatile substances (e.g. soot) were also produced. When using alumina-ceramic particles, acetylene was the main product with none or traces of other C2 hydrocarbons. In the presence of Pt/Al2O3, however, much more ethylene and ethane were produced.

Wear and Nanomechanical Studies of Silicon Oxide and Silicon Nitride Thin Films for MEMS Applications

Thin films produced by PE-CVD techniques are often used in microelectronic and MEMS applications. New kind of discharges, glow discharges so called Atmospheric Pressure Glow (APG) can be otained when a dielectric barrier is used. The process of discharges stabilized by a dielectric barrier having non-uniform character (similar to the “silent” discharges) was used to produce thin films of silicon oxide and silicon nitride applicable in MEMS technology. The substrate temperature (silicon or metal) was usually 150-250°C. Such film deposited using polycondensation of tetraethoxysilane (TEOS) and hexamethylodisilazane (HMDS) for silicon oxide and silicon nitride respectively were tested using a special microtribometer for wear studies and Hysitron Inc.Triboscope TM which has the capability to carry out indentations at very low loads and to make load-displacement measurements with subnanometer indentation depth sensitivity. The wear and nanomechanical behaviors of the films were found to be very sensitive to the thickness (films up to 300 nm thick have been investigated) and the material composition.

Cobalt catalyst for ammonia oxidation modified by heat treatment

Abstract Heat treatment of the cobalt oxide catalyst is a substantial condition for obtaining theproduct of high activity and of sufficient mechanical strength. It was shown that the porous structure of catalyst grains, produced in the course of heat treatment, is one of the parameters responsible for catalytic activity. The volume of the coarse pores (0.5–1 μm in radius) is of primary importance for the performance of the catalyst.