Novel Catalytic Dielectric Barrier Discharge Reactor for Gas-Phase Abatement of Isopropanol

Catalytic gas-phase abatement of air containing 250 ppm of isopropanol (IPA) was carried out with a novel dielectric barrier discharge (DBD) reactor with the inner catalytic electrode made of sintered metal fibers (SMF). The optimization of the reactor performance was carried out by varying the voltage from 12.5 to 22.5 kV and the frequency in the range 200–275 Hz. The performance was significantly improved by modifying SMF with Mn and Co oxide. Under the experimental conditions used, the MnO _x /SMF showed a higher activity towards total oxidation of IPA as compared to CoO _x /SMF and SMF electrodes. The complete destruction of 250 ppm of IPA was attained with a specific input energy of ∼235 J/L using the MnO _x /SMF catalytic electrode, whereas, the total oxidation was achieved at 760 J/L. The better performance of the MnO _x /SMF compared to other catalytic electrodes suggests the formation of short-lived active species on its surface by the in-situ decomposition of ozone.     

Formation of the surface NO during N2O interaction at low temperature with iron-containing ZSM-5

Interaction of N2O at low temperatures (473-603 K) with Fe-ZSM-5 zeolites (Fe, 0.01-2.1 wt %) activated by steaming and/or thermal treatment in He at 1323 K was studied by the transient response method and temperature-programmed desorption (TPD). Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) of NO adsorbed at room temperature as a probe molecule indicated heterogeneity of surface Fe(II) sites. The most intensive bands were found at 1878 and 1891 cm(-1), characteristic of two types mononitrosyl species assigned to Fe2+(NO) involved in bi- and oligonuclear species. Fast loading of atomic oxygen from N2O on the surface and slower formation of adsorbed NO species were observed. The initial rate of adsorbed NO formation was linearly dependent on the concentration of active Fe sites assigned to bi- and oligonuclear species, evolving oxygen in the TPD at around 630-670 K. The maximal coverage of a zeolite surface by NO was estimated from the TPD of NO at approximately 700 K. This allowed the simulation of the dynamics of the adsorbed NO formation at 523 K, which was consistent with the experiments. The adsorbed NO facilitated the atomic oxygen recombination/desorption, the rate determining step during N2O decomposition to O2 and N2, taking place at temperatures > or =563 K.     

Stabilization mechanism of TiO2 on flexible fluorocarbon films as a functional photocatalyst

The repetitive discoloration kinetics of the azo-dye Methyl Orange (taken as a model organic compound) was followed under solar simulated radiation (90 mW/cm²) to assess the performance of the TiO₂/Tedlar^® composite photocatalyst. The influence of solution parameters on the photo-discoloration process: pH, dye concentration, applied light intensity and concentration of H₂O₂ were systematically investigated. During the photocatalysis a modification occurs in the TiO₂/Tedlar^® composite due to the TiO₂ interaction with the Tedlar^® film. Physical insight is given for the stabilization mechanism of the TiO₂ particles in the Tedlar matrix based on the data obtained by X-ray photoelectron spectroscopy (XPS). The F 1s peak of the Tedlar film indicates that the TiO₂ is loaded on the Tedlar fluoro-groups. The loading of TiO₂ on the 75 μm thick Tedlar^® film was 0.9% (w/w) as determined by atomic absorption spectrophotometry (AAS). Attenuated total reflection infrared spectroscopy (ATRIR) shows no formation of additional bands within the photodiscoloration reaction. This shows that an efficient catalysis taking place on the TiO₂/Tedlar^® surface. The rugosity (mean square roughness, rms) of the TiO₂/Tedlar^® film was determined by atomic force microscopy (AFM) to be 19.7 nm. This value remained constant during long-term operation. Transmission electron microscopy (TEM) reports the thickness and coverage of TiO₂ Degussa P-25 on the Tedlar^® surface before and after photocatalysis.