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.     

On the reactions of methyl radicals with nitrilotris(methylenephosphonic-acid) complexes in aqueous solutions

Abstract

The reactions of methyl radicals with M^II-(ntp)(H₂O)₂ complexes were studied. The formation of an unstable intermediate (ntp)(H₂O)M^III-CH₃ is observed. This reaction is an equilibrium process, i.e. the M^III-C bond decomposes via homolysis. The (ntp)(H₂O)M^III-CH₃ complexes isomerize to a more stable form. The results compared to those obtained in analogous reactions of the M^II-(nta)(H₂O)₂ complexes were shown to be similar with one exception – for the nta complexes no isomerization process is observed.     

The Structural Systematics of Protonation of Some Important Nitrogen‐base Ligands. I Some Univalent Anion Salts of Doubly Protonated 2, 2′:6′, 2″‐Terpyridyl

A number of salts of 2,2′:6′,2″ ‐terpyridyl (‘tpy’) with univalent anions (halides : X = Cl, Br, I; oxyanions of increasing basicity: ClO₄, NO₃, ‘tfa’ = trifluoroacetate, ‘tca’ = trichloroacetate), variously solvated, have been structurally characterized by single crystal X‐ray studies. In all cases the tpy moieties are found to be doubly protonated [tpyH₂]²⁺, the hydrogen atoms being associated with the nitrogen atoms of the peripheral rings, these together with the central nitrogen atom being directed towards a common focus, in most cases ‘chelating’ one of the counter‐ion components in diverse ways. Thus the chloride and bromide compounds are isomorphous [(tpyH₂)X]⁺X⁻·H₂O arrays; a second dihydrate phase is also described for the chloride, the two forms having the unchelated anion and water molecules engaged in hydrogen‐bonded networks essentially independent of [(tpyH₂)X]⁺. The iodide is anhydrous, and of a different structural type, the anions, presumably too large for chelation, lying out of plane to either side, and linking different cations into a one‐dimensional polymer; in the perchlorate, the unsolvated aggregate is now discrete [(tpyH₂)X₂], a pair of perchlorate ions disposed to either side of the tpy plane, lying each with one oxygen atom interacting with both of the two protonating hydrogen atoms. In the anhydrous X = NO₃, tfa, tca arrays, the lattices are solvated by the parent acids; one oxygen atom of each anion is chelated by the [tpyH₂]²⁺ as in the chlorides, the other anion, with the acid, forming an independent ‘acid salt’ counterion [XHX]⁻ in each case, retaining the additional protonic hydrogen rather than further protonating the central ring, all being of the form [(tpyH₂)X]X·HX = [(tpyH₂)X][X(HX)].     

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.     

Theoretical study of the amazing firefly bioluminescence: the formation and structures of the light emitters

Reaction mechanisms for the formation of the keto-form of oxyluciferin (OxyLH(2)) from the luciferin of fireflies via a dioxetanone intermediate are predicted using the B3LYP/6-31G theoretical method. The ring opening of a model dioxetanone and the decarboxylation proceed in one step via a singlet diradical transition structure with an activation barrier of 18.1 and an exothermicity of 90.8 kcal/mol. The S(0) --> S(1) vertical excitation energies predicted with time dependent density functional theory, TDDFT B3LYP/6-31+G, for the anionic and neutral forms of OxyLH(2) are in the range of 60 to 80 kcal/mol. These energetic results support the generally accepted theory of chemically initiated electron exchange luminescence (CIEEL). The chemical origin of the multicolor bioluminescence from OxyLH(2) is examined theoretically using the TDDFT B3LYP/6-31+G, ZINDO//B3LYP/6-31+G, and CIS/6-31G methods. A change in color of the light emission upon rotation of the two rings in the S(1) excited state of OxyLH(2) is unlikely because both possible emitters, the planar keto- and enol-forms, are minima on the S(1) potential energy surface. The participation of the enol-forms of OxyLH(2) in bioluminescence is plausible but not required to explain the multicolor emission. According to predictions at the TDDFT B3LYP level, the color of the bioluminescence depends on the polarization of the OxyLH(2) in the microenvironment of the enzyme-OxyLH(2) complex.     

Hyper-Cross-Linked Polystyrene as a Stabilizing Medium for Small Metal Clusters

Among different polymers nanostructured cross-linked aromatics have the greatest potential as catalytic supports due to their exceptional thermal and chemical stability and preservation of the active phase morphology. This work studies the ability of hyper-cross-linked polystyrene (HPS) to stabilize small Pd_n and Pt_n (n = 4 or 9) clusters. Unrestricted DFT calculations were carried out for benzene (BZ) adsorption at the BP level of theory using triple-zeta basis sets. The adsorption of BZ rings (stepwise from one to four) was found to result in noticeable gain in energy and stabilization of resulting adsorption complexes. Moreover, the interaction of metal clusters with HPS micropores was also addressed. For the first time, the incorporation of small clusters in the HPS structure was shown to influences its geometry resulting in the stabilization of polymer due to its partial relaxation.