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: Based on a dimensional analysis of flow rate in nanoenvironment, the aggregate response of a nanoporous particle subjected to a dynamic pressure is studied in context of effective phase transformation. The numerical results indicate that in the early stage the system behavior is mostly determined by the nucleation and associated growth of saturated pore clusters (SPCs), while in the late stage the SPC coalescence becomes predominantly important. The relations between the absorption time and the sizes of the particle and the pores are highly nonlinear.Journal of Mathematical Chemistry 12/2004; 37(2):93-99. DOI:10.1007/s10910-004-1442-z · 1.27 Impact Factor
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ABSTRACT: We present a study of the use of amine- functionalised, mesoporous silicas as supports for nanoparticulate palladium, and the use of the composite materials as heterogeneous catalysts for the Suzuki coupling of aryl bromides. Upon modification of the silica, via attachment of N-functionalised aminopropylsilyl ethers to surface silanol groups, only a small reduction in surface area and average pore diameter is observed. The mesoporosity and high surface area are also maintained after introduction of nanoparticulate palladium, as evidenced by the measurement of BET nitrogen sorption isotherms. Electron microscopy shows that the palladium particles are well-dispersed and of typical diameter 3-6 nm. Catalysis was initially tested using the coupling of phenylboronic acid with 4-bromoanisole in the presence of K2CO3 and with toluene as solvent. This revealed that the choice of organic modification has a crucial role in determining the activity and recyclability of the catalyst: optimum behaviour was found for diamine- and triamine-containing systems, while quaternary alkylammonium salts showed poor activities. The optimised catalysts are also active in the coupling of a range of aryl bromides and phenylboronic acids, and after three catalytic runs they show virtually no drop in activity. Upon further cycling, however, and after six catalytic runs, we do observe a drop in activity and this is accompanied by some leaching of palladium, and pore-blocking by reaction products and byproducts.Chemistry of Materials 02/2005; 17(4). DOI:10.1021/cm048860s · 8.54 Impact Factor
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ABSTRACT: In this paper, multi-wall carbon nanotubes (MWNTs)/Pt microparticles nanocomposite was prepared by electrodepositing Pt microparticles onto the MWNTs matrix. The surface of glassy carbon electrode was modified with this kind of nanocomposite for measurement of thiols, such as L-cysteine (L-Cys) and glutathione (GSH). Compared with the MWNTs or Pt microparticles modified electrode, the nanocomposite modified electrode exhibited high sensitivity and good stability for detection of thiols. According to the results of experiments, the peak currents of L-Cys and GSH are linear with their concentrations and the detection limits (S/N=3) are 2.9 x 10(-8) mol/L and 4.5 x 10(-8) mol/L, respectively. Coupled with microdialysis, the method has been successfully applied to the determination of these two thiols in rat striatal microdialysates.Journal of Chromatography B 04/2005; 817(2):239-46. DOI:10.1016/j.jchromb.2004.12.014 · 2.69 Impact Factor