LM Bronstein, DM Chernyshov, RL Karlinsey, JW Zwanziger, VG Mateeva, EM Sulman, GN Demidenko, HP Hentze, M Antonietti. Mesoporous alumina and aluminosilica with Pd and Pt nanoparticles: Structure and catalytic properties. Chemistry of Materials 15(13), 2623 (2003).
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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