Pd(II)-Catalyzed cyclogeneration of carbocations: subsequent rearrangement and trapping under oxidative conditions

A catalytic oxidative polycyclization reaction initiated by the carbocyclization of 1,5-dienes with Pd(II) is reported. Trapping of a putative carbocation with suitable functional groups (phenols, alkenes, alcohols, sulfonamide), or rearrangement protocols (Pinacol) yields poly-cyclic products in good yields and in excellent diastereoselectivities. Turnover of the intermediate Pd-C bond is via β-H elimination.     

Polyatomic anion versus acetonitrile in coordinating ability: structural properties of AgX-bearing 1,4-bis(2-isonicotinoyloxyethyl)piperazine (X??=?NO3?, CF3SO3?, ClO4?, BF4?, and PF6?)

Type studies on competitive polyatomic anion versus acetonitrile coordination in the self-assembly of a series of [Ag₂(X) _m (bip)(NCCH₃) _n ](X)_2−m (X⁻ = NO₃ ⁻, CF₃SO₃ ⁻, ClO₄ ⁻, BF₄ ⁻, and PF₆ ⁻; m = 0, 2; n = 0, 2, 4; bip = 1,4-bis(2-isonicotinoyloxyethyl)piperazine) were carried out. Each bip spacer acts as an N₄ tetradentate ligand and is linked to four silver(I) centers through two pyridine and two piperazine moieties, producing a double strand consisting of two 20-membered ring units. The coordinating environment around the silver(I) center is subtly determined by the competition of the polyatomic anions with acetonitrile, that is, by the Ag···NCCH₃ versus Ag···X interactions. The coordinating ability of acetonitrile is inversely proportional to the order of the coordination ability of the Hoffmeister series of polyatomic anions, NO₃ ⁻ ≫ CF₃SO₃ ⁻ > ClO₄ ⁻ > BF₄ ⁻ ≫ PF₆ ⁻.     

Electrochemically programmed chemodosimeter on ultrathin platinum films

We demonstrate electrochemically controlled release of chemodosimeters attached to ultrathin patterned platinum electrodes. Fluorescence and electrochemical methods have been employed for the detection of chemodosimeter modification/desorption and Cu(2+) binding/removal.     

Thermal characterization and compatibility studies of perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) oxide with Cr2O3 at high temperature

The chemical compatibility of perovskite-type Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ (BSCF) oxides with Cr₂O₃ has been examined between room temperature and 1,100 °C. Differential thermal analysis and thermogravimetric analysis were used to analyze the thermal behavior of BSCF–Cr₂O₃ binary mixtures in all composition ranges (0–100 mass% BSCF). The reaction products were identified by X-ray analysis after heating at 700–1,100 °C. As we expected, it was found that perovskite-type BSCF oxide had a poor chemical compatibility with the Cr₂O₃ oxide. In particular, the decomposition process of the BSCF–Cr₂O₃ binary mixture is quite complex and it starts at about 700–750 °C. The mixtures of BSCF and Cr₂O₃ oxides reacted forming mixed complex oxides based on (Ba/Sr)FeO₃, (Co/Fe)CrO₄, and (Ba/Sr)CrO₄ mixtures.     

Syngas conversion beyond chemical equilibrium by in situ bimolecular reaction

An in situ bimolecular reaction, in which syngas is fed with toluene as a secondary reactant (hereafter Tol in situ methylation), was studied over bifunctional catalysts comprised of methanol synthesis catalyst and H-ZSM-5 in a fixed-bed down-flow reactor at 460 psig. When physically mixed with H-ZSM-5 to form bifunctional catalysts, CrZ_HZ (Cr₂O₃/ZnO + HZSM-5) catalyst showed much higher activity than CZA_HZ (CuO/ZnO/Al₂O₃ + H-ZSM-5) in the Tol in situ methylation, while CrZ catalyst exhibited substantially lower activity than CZA in methanol synthesis. CO conversion to methanol in the Tol in situ methylation was estimated by Bz in situ methylation. The CO conversion to methanol was calculated to be in the range of 11–27 %, while that in methanol synthesis over CrZ was about 5 % at most due to chemical equilibrium limitation. By employing a silicalite-coated H-ZSM-5 (Sil/HZ) in bifunctional catalyst, xylene selectivity and para-xylene yield were much improved in the Tol in situ methylation.     

Effect of potassium addition on bimetallic PtSn/θ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst for dehydrogenation of propane to propylene

PtSn/θ-Al₂O₃ catalysts with different amounts of K (0.14, 0.22, 0.49, 0.72, and 0.96 wt%) are prepared to investigate the K effects on the PtSn catalyst in propane dehydrogenation (PDH). KPtSn catalyst with 0.xx wt% K, 0.5 wt% Pt and 0.75 wt% Sn is designated as xx-KPtSn. PDH was performed at 873 K and a gas hourly space velocity (GHSV) of 53,000 mL/g_cat h. The temperature-programmed desorption (NH₃-TPD), temperature-programmed reduction (TPR) and CO chemisorption of the KPtSn catalysts with K added revealed the potassium addition blocked the acid sites, promoted the reduction of Sn oxide and decreased the Pt dispersion. The formations of cracking products and higher hydrocarbons on acid sites were suppressed by the K effect of blocking the acid sites. In contrast, K addition at more than 0.72 wt% rather increased cracking products and the amount of coke, resulting in the severe deactivation of catalysts. The high cracking products on the KPtSn catalysts with the high amount of K should not be related to the acid sites, because the acid sites were monotonously decreased with an increase in the amount of K. Instead, the potassium affected the characteristics of PtSn. The interaction between Pt and Sn could be weakened by enriching the reduced Sn, because the K component promoted the reduction of Sn oxide in the TPR experiments. Therefore, the 14-KPtSn catalyst with the low amount of K exhibits the highest stability and selectivity among the prepared KPtSn catalysts due to the compromise of the advantageous (blocking the acid sites) and bad (weakening the interaction between Pt and Sn) effects of the K addition in PDH.     

Preparation of blue-emitting CaMgSi2O6:Eu phosphors in reverse micellar system and their application to transparent emissive display devices

Blue-emitting Eu²⁺-doped CaMgSi₂O₆ phosphors were prepared by the reverse micelle method. The resultant particles were nanocrystalline with a grain size of about <300 nm and exhibited a characteristic blue emission spectrum centered at 445 nm induced by the oxygen coordinated Eu²⁺ ions. By using the corresponding nanophosphors followed by the formation of a uniform phosphor layer, we have demonstrated the mini-sized transparent plasma-discharge panels and investigated their luminance characteristics. Phosphor coated panel is properly transparent, ≥65%, at the visible wavelength region and illuminates a characteristic blue emission under Ne/Xe plasma discharge conditions. Thus, we can obtain a fast decaying, robust blue-emitting silicate phosphor layer under excited plasma radiation for upcoming emissive display devices like as transparent and three-dimensional plasma display panels.     

Activation of ultrathin oxide films for chemical reaction by interface defects

Periodic density functional theory calculations revealed strong enhancement of chemical reactivity by defects located at the oxide-metal interface for water dissociation on ultrathin MgO films deposited on Ag(100) substrate. Accumulation of charge density at the oxide-metal interface due to irregular interface defects influences the chemical reactivity of MgO films by changing the charge distribution at the oxide surface. Our results reveal the importance of buried interface defects in controlling chemical reactions on an ultrathin oxide film supported by a metal substrate.     

Analytical issues in monitoring drinking-water contamination related to short-term, heavy rainfall events

Heavy rainfall events, increasing in frequency and intensity with climate change, impact on the quality of the water resource used for drinking-water production. Small-scale water suppliers are particularly sensitive because of their management and the related difficulties of adapting treatment to variations. Decision-support systems, based on monitoring and analytical tools, need to be developed to improve crisis-management procedures related to such events. After presenting the issues related to heavy rainfall events, the article summarizes the tools currently used for quality control of drinking water within this framework, the need for developments and other requirements.