Mesoporous Alumina and Aluminosilica with Pd and Pt Nanoparticles:  Structure and Catalytic Properties

Chemistry of Materials, v.15, 2623-2631 (2003) 05/2003; DOI: 10.1021/cm021776x

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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