Phosphotungstic heteropoly acid as efficient heterogeneous catalyst for solvent-free isomerization of a-pinene and longifolene.

Silica-supported H3PW12O40 (PW), the strongest heteropoly acid in the Keggin series, is an efficient, environmentally friendly heterogeneous catalyst for the liquid-phase isomerization of a-pinene and longifolene into their more valuable isomers – camphene and isolongifolene, respectively, which are intermediates in the synthesis of expensive fragrances. The reactions occur under solvent-free conditions in the temperature range of 80–100 8C, with low catalyst loadings (0.15–5 wt%) and high turnover numbers (up to 6000 per proton). The catalyst can be easily recovered and reused. No PW leaching is observed in the reaction system

Gold, palladium and gold-palladium supported on silica catalysts prepared by sol-gel method: synthesis, characterization and catalytic behavior in the ethanol steam reforming

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Noble-metal-based catalysts supported on silica (Au/SiO2, Pd/SiO2 and Au-Pd/SiO2) were prepared by the sol-gel method and were evaluated in the steam reforming of ethanol for hydrogen production. The catalysts were characterized by N-2 physisorption (BET/BJH methods), X-ray diffraction, temperature programmed reduction analysis, H-2 chemisorption, atomic absorption spectrophotometry and Raman spectroscopy. The structural characterization of the Au- and Pd-containing catalysts after calcination showed that the solids are predominantly formed by Au-0, Pd-0 and PdO species and was observed that the metallic Pd dispersion diminished in the presence of Au-0. The results revealed that the catalytic behavior could be influenced by the experimental conditions and the nature of the catalyst employed. The Pd/SiO2 catalyst showed the best performance among the catalysts tested at the highest reaction temperature (600 A degrees C) due to the more effective action of the metallic active phase, which covers a greater area in this sample. At this same reaction temperature, the Au-Pd/SiO2 catalyst showed a significant deactivation, probably due to the lower Pd dispersion presented by this catalyst.672273281Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)FINEPFundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Isomerization of a-pinene oxide over cerium and tin catalysts : selective synthesis of trans-carveol and trans-sobrerol.

A remarkable effect of the solvent nature on the acid catalyzed transformation of _-pinene oxide allowed direction of the reaction to either trans-carveol or trans-sobrerol. Each of these highly valuable compounds was obtained in nearly 70% yield using an appropriate polar solvent, whose basicity affected strongly the product distribution. In acetone, a weakly basic solvent, the reaction over heterogeneous sol–gel Sn/SiO2 or Ce/SiO2 catalysts gave mainly trans-sobrerol. No leaching of active components occurs under the reaction conditions and the catalysts can be recovered and reused. On the other hand, in more basic solvent, i.e., dimethylacetamide, the reaction was essentially directed to trans-carveol. Due to the leaching problems with Sn/SiO2 and Ce/SiO2 materials, the synthesis of trans-carveol was performed under homogeneous conditions using CeCl3 or SnCl2 as catalysts with a catalyst turnover number up to ca. 1200. The method represents one of the few examples of the synthesis of isomers from _-pinene oxide, other than campholenic aldehyde, with a sufficient for practical usage selectivity

Preparation, Structural Characterization And Catalytic Properties Of Co/ceo 2 Catalysts For The Steam Reforming Of Ethanol And Hydrogen Production

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Air stable ligandless heterogeneous catalyst systems based on Pd and Au supported in SiO2 and MCM-41 for Suzuki–Miyaura cross-coupling in aqueous médium.

Palladium and palladium-gold containing siliceous-MCM-41 and sol–gel palladium and palladium-gold silica composites have been prepared. The catalytic performance of incorporated Pd/MCM-41, Au- Pd/MCM-41 and Pd and Au-Pd/SiO2 sol–gel catalysts for the Suzuki–Miyaura cross-coupling reaction was determined and the influence of the matrix and the catalyst composition on the catalytic activity were also studied. The catalysts were characterized by N2 physisorption (BET/BJH methods), X-ray diffraction, temperature programmed reduction analysis, H2 chemisorption, atomic absorption spectrophotometry and Raman spectroscopy. The silica-containing palladium and palladium-gold catalysts prepared using the MCM-41 matrix showed greater catalytic activity than using the conventional sol–gel method; however, gold had a significant influence on this reaction. The catalyst did not undergo metal leaching and could be easily recovered and re-used (reused)

A new use for modified sugarcane bagasse containing adsorbed Co2+and Cr3+ : catalytic oxidation of terpenes.

This study describes the applicability of two chemically modified sugarcane bagasses containing eitheradsorbed Co2+or Cr3+ions as heterogeneous catalysts for the autooxidation of monoterpenes. The mainobjective was to investigate new uses for these adsorbent materials which had been previously employedfor treatment of aqueous solutions or effluents containing metals such as Co2+and Cr3+. The adsorptionefficiency of Co2+and Cr3+on SCB2 and EB was evaluated by adsorption isotherms and other techniquessuch as XRD, ICP-AES and TGA. Catalytic activity of the four new catalysts, SCB2-Co, SCB2-Cr, EB-Co, andEB-Cr, were assessed in the oxidation reaction of _-citronellol(1), (+)-limonene(2), and (−)- _-pinene(3)in a free solvent system. Results obtained demonstrated that these materials were promising catalysts forthe oxidation of monoterpenes. Reactant conversion ranged from 49 to 78% as determined by GC analysisand a combined selectivity up to 59% for the oxidation products was achieved