Mesoporous Alumina and Aluminosilica with Pd and Pt Nanoparticles: Structure and Catalytic Properties
ABSTRACT Cationic and anionic microgels based on sulfonated polystyrene and poly(ethylmethacryltetramethylammonium chloride) and containing Pd and Pt nanoparticles were used as templates along with polystyrene-block-poly(ethylene oxide) block copolymers for casting nanoporous alumina and aluminosilica with nanoparticles. The Pt-nanoparticle-containing aluminosilica consists of interpenetrating pores and Pt particles of 7 nm in diameter (by X-ray diffraction) located in the interpore channels. Pd nanoparticles are smaller and partially block the pore entrances of Pd-nanoparticle-containing aluminosilica, decreasing the porosity. Metal-particle-containing aluminas templated both over cationic and anionic microgels consist of an interpenetrating pore system and alumina nanowires (2−3 nm in diameter and about 40 nm in length) along with Pd or Pt nanoparticles. This combination creates higher mesoporosity than for aluminosilicas. The 27Al MAS NMR spectra of metal-nanoparticle-containing alumina show two distinct sites at 0 and 65 ppm independently of metal or microgel types, indicating octahedral and tetrahedral coordination, respectively; the octahedral species strongly prevail. The aluminum spectra of all aluminosilica samples show a more complicated picture, with octahedral and tetrahedral aluminum along with probable pentacoordinated species. The catalytic properties of Pd(Pt)-nanoparticle-containing aluminas and aluminosilicas were studied in partial hydrogenation of three amphiphilic acetylene alcohols having a different length of the hydrophobic tail. The aluminosilicas showed low activity and selectivity for all substrates, while Pd-particle-containing aluminas displayed high activity and selectivity, especially for acetylene alcohol with the longest aliphatic tail (dehydroisophytol, acetylene alcohol C20).
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ABSTRACT: Iro (III)-entrapped gamma-alumina nanosorbents were prepared by an environmentally benign method using an ionothermal process based on an ionic liquid to synthesize the gamma-alumina host and a sonochemical method to entrap the iron(III) guest. The morphology of the alumina depends on the aluminum precursor used, giving aligned bundled and randomly debundled gamma-alumina nanorods as well as wormlike mesoporous alumina. In particular, the rodlike structure shows significantly greater mesoporosity than the wormlike porous gamma-alumina structure. Moreover, entrapment of iron(III) in the gamma-alumina nanosorbents with randomly debundled rodlike structures leads to the greatest AsV removal capacity and the fastest adsorption rate as compared to the other FeIII-entrapped adsorbents, as a result of its larger surface area and pore sizes. Thus, this method provides a clean and effective route to an advanced host-guest adsorbent system for application in the removal of arsenic from drinking water.ChemSusChem 02/2008; 1(4):356-62. · 7.48 Impact Factor
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ABSTRACT: Palladium nanoparticles are prepared from palladium(II) acetate and 2 equivalents of potassium tert-butoxide in the presence of 4-octyne. The palladium nanoparticles-tetrabutylammonium borohydride system shows excellent catalytic activity and selectivity in the semihydrogenation of alkynes to the [(Z)-]alkenes. The hydrogenation of 4-octyne is conducted with the catalyst system at a substrate-to-palladium molar ratio of 10,000–200,000 under 8 atm of hydrogen to give (Z)-4-octene in>99% yield. Isomerization and over-reduction of the Z-alkene are very slow even after consumption of the alkyne.Advanced Synthesis & Catalysis 12/2009; 351(18):3143 - 3149. · 5.54 Impact Factor
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ABSTRACT: The H-shaped block copolymers (PTMSPMA)2-PEG(PMPSTMSPMA)2 with two compositions, (EG)91-b-(TMSPMA)92 and (EG)455-b-(TMSPMA)176 have been successfully synthesized by atom transfer radical polymerization (ATRP) of tri(methoxylsilyl)propyl methacrylate (TMSPMA) at room temperature in methanol. The initiation system applied was composed of 2,2-bis(methylene α-bromoisobutyrate)propionyl terminated poly(ethylene glycol) (Br2PEGBr2) with M n = 4000 or 2000, CuBr and 2,2′-bipyridine. The macroinitiator, Br2PEGBr2, was prepared by the reaction of two hydroxyl groups terminated PEG with 2,2-bis(methylene α-bromoisobutyrate)propionyl chloride. The NMR spectroscopy and GPC measurements were used to characterize the structure and molecular weight and molecular weight distribution of the resultant copolymers. The H-shaped block copolymers Sam 1 and Sam 2 were self-assembled in DMF/water mixtures and then the trimethoxysilyl groups in PTMSPMA were cross-linked by condensation reaction in the presence of triethylamine. Stable large-compound vesicles with 10 nm diameter of cavities were formed for Sam 1 which contains a short PEG chain. However, the self-assembling of the Sam 2 in the selective solvents resulted in big vesicles aggregates. These two different morphologies of aggregates are attributed to their relative chain length of water soluble PEG. The vesicles formed from Sam1 with short PEG chains have big surface energy which will lead them to self-assemble further, forming large-compound vesicles.Frontiers of Chemistry in China 11/2008; 3(4):480-484.