N. E. Strokova

Catalytic properties of CexZr1–xO2 prepared using a template in the oxidation of CO

The catalytic activity in CO oxidation of CexZr1–xO2 double oxides prepared using pine sawdust and cetyltrimethylammonium bromide (CTAB) as templates is compared. It is found by means of SEM and the low-temperature adsorption of N2 that biomorphic oxides reproduce the macropore structure of the template. It is shown via XRD and Raman spectroscopy that all samples contained mixed ceria-zirconia oxide. The double oxides form a cubic phase with a lattice of the fluorite type at a ratio of Ce: Zr = 4, regardless of the nature of the template; when Ce: Zr = 1, the biomorphic mixed oxide forms a tetragonal phase. According to Raman spectroscopy and XRD it was shown that the distortion of the oxygen sublattice is higher in biomorphic samples. Energy dispersive analysis shows that Ca impurities were present in the biomorphic samples, introducing additional distortions in the lattice of double oxide and leading to the formation of anionic vacancies. It is found that when Ce: Zr = 4, the conversion of CO on biomorphic oxide in the range of 100–350°C is higher than that observed for CexZr1–xO2 (CTAB); reducing the Ce: Zr ratio in the biomorphic sample to 1 results in a marked decrease in CO conversion at 100–200°C. It is concluded that these differences are due to changes in the mobility of the lattice oxygen.

Modeling the interaction of ozone with chloroform and bromoform under conditions close to stratospheric

The reactions of ozone with chloroform and bromoform are studied using a flow gas discharge vacuum unit under conditions close to stratospheric (temperature range, 77-250 K; pressure, 10−3-0.1 Torr in the presence of nitrate ice). It is shown that the reaction with bromoform begins at 160 K; the reaction with chloroform, at 190 K. The reaction products are chlorine and bromine oxides of different composition, identified by low-temperature FTIR spectroscopy. The presence of nitrate ice raises the temperature of reaction onset to 210 K.

Specific features of the adsorption of chlorinated methanes and water on carbon nanotubes and alumina

The adsorption of CH2Cl2, CH3Cl, CCl4, and H2O vapors on the surface of multi-walled carbon nanotubes and alumina in the temperature range of 10—25 °C was studied. Dependences of the isosteric heat of adsorption on the surface coverage were plotted. The initial heat of adsorption of dichloromethane, chloroform, and CCl4 on Al2O3 was found to be equal to 71, 28, and 31 kJ mol–1, respectively. In most cases, adsorption on the oxide adsorbent was characterized by a higher heat of adsorption compared to that found on the carbon material, which is apparently related to chemical interaction of sorbed molecules with the OH groups of the alumina surface.

Sawdust as an effective biotemplate for the synthesis of Ce0.8Zr0.2O2 and CuO–Ce0.8Zr0.2O2 catalysts for total CO oxidation

Wood sawdust (SD) was successfully used as a biotemplate to prepare precursors of Ce0.8Zr0.2O2 (CZ) and CuO–Ce0.8Zr0.2O2 (Cu–CZ, about 25% of CuO) catalysts, which were tested in total CO oxidation at 100–400 °C after calcination at 500 or 600 °C, and compared with analogous systems prepared using cetyltrimethylammonium bromide (CTAB). The improved specific surface area and oxygen mobility of the catalysts calcined at 500 °C resulted in an increased efficiency in CO oxidation. CZ (SD-500) demonstrated much higher catalytic efficiency than the CZ (CTAB-500) sample despite having a two times less SBET due to the promoting action of Ca and K inherited from sawdust and improved concentration of superoxide surface centers. Both facilitation of CO adsorption on peroxide and superoxide centers and increased oxygen mobility provide improvement in the high-temperature efficiency of biomorphic CZ in CO oxidation. The XRD, XPS and TPR data testify that Cu in modified systems partially exists as a separate CuO phase, in small amounts as Cu+, and partially is incorporated in the surface CuyCexZr1−x−yO2−z and/or CuyCe1−yO2−x phases. Modification with Cu enhances the low-temperature efficiency of CZ systems, prepared using both templates and calcined at 500 °C. Cu–CZ (SD-500) was a bit less active than Cu–CZ (CTAB-500) only at 100–150 °C, primarily due to the decreased CuO content, and the difference in CuO interaction with CZ support, found by TPR. Presumably CuO provides low-temperature CO oxidation through the Langmuir–Hinshelwood mechanism; the Cu+/Cu2+ pair can also participate as an additional redox pair in high-temperature CO oxidation by the Mars–van-Krevelen mechanism.

Sintered Carbon Nanomaterials: Structural Change and Adsorption Properties

Abstract Porous powdered carbon nanomaterials [carbon nanotubes (CNT) and carbon nanoshells (CNS)] were compacted using spark plasma sintering (SPS) technique. High resolution transmission electron microscopy (HRTEM) and SEM images demonstrate the structural change: the increase of density and thickness of nanoshells stack, formation of interparticle bonds between nanotubes. Surface properties of original and sintered materials were studied by liquid nitrogen sorption and compared to the characteristics for real vapors sorption. The data collected for water, ethanol, acetonitrile and benzene show both physical adsorption and chemisorption. The mean pore diameter distribution calculated from nitrogen adsorption by density functional theory (DFT) approach shows the reduction of total pore volume in CNS pellet while for CNT pellet total pore volume does not differ dramatically from those for non-compacted samples. The isosteric heats of sorption for all chosed vapors were calculated.

Laboratory simulations of the interaction between ozone and chloroacetic acids in the conditions close to stratospheric

The interaction between ozone and mono-, di-, and trichloroacetic acids are studied using a flow vacuum gas discharge setup in a regime close to stratospheric conditions (in the temperature range of 77 to 250 K, at pressures of 10−3 to 0 Torr, and in the presence of ice). The interaction between ozone and trichloroacetic acid starts at 77 K, while interaction with monochloroacetic acid begins when the temperature is raised to 200 K. The reactions are assumed to proceed via different mechanisms: chlorine oxides of different composition are the reaction products, as is shown using low-temperature IR spectroscopy. Preliminary adsorption of the acids on a surface of ice raises the temperature of interaction to 190 K.