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: The synthesis of organized mesoporous aluminas has opened a very interesting area for application of this type of materials, particularly as catalysts or catalyst supports. This review focuses on the individual synthesis routes to produce organized mesoporous aluminas with large surface areas and narrow pore size distributions, and on the evaluation of their textural, chemical and thermal properties and outlines examples of catalytic applications of organized mesoporous alumina-based catalysts. We tried to rationalize the synthetic approaches to prepare organized mesoporous aluminas, to relate their properties to synthetic procedures used as well as to their catalytic behavior in different reactions. Utilization of various structure-directing agents for "cationic," "neutral," "anionic," "nanocasting," and special approaches leading to scaffolding and lathlike organized mesoporous aluminas is discussed in the first part of this review, as well as textural and structural characterization and thermal stability of mesoporous aluminas synthesized by different synthetic approaches. In the second part, catalytic applications of organized mesoporous aluminas described in the open literature are evaluated from the standpoint of the importance of these reactions for technological applications.Catalysis Reviews 05/2008; 50(2):222-286. · 6.11 Impact Factor
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ABSTRACT: We demonstrate for the first time herein that electrospinning of soluble crosslinked polymer particles (microgels) is feasible and that it can be used to obtain micron-sized fibers from these macromolecules. Most notably, the electrospinning approach is found to be successful also in the case of microgels bearing metal nanoclusters, and allows to prepare composite fibers containing a homogeneous dispersion of metal nanoparticles without alterations in the nanoparticle size and size distribution. Given the broad applicability of microgels as exotemplates and stabilisers for inorganic nanoparticles, the proposed preparation method stands out as a novel, general approach for the synthesis of potentially useful composite fibers containing inorganic nanoparticles.Polymer 12/2009; 50(26):6193 - 6197. · 3.77 Impact Factor
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ABSTRACT: Noble metal nanoclusters stabilised by N,NN,N-dimethylacrylamide-based soluble cross-linked polymers (microgels) have been prepared and tested as catalysts in the selective oxidation of secondary alcohols to the corresponding carbonyl compounds with molecular oxygen in water. Pd nanoclusters turned out to be superior catalysts compared with nanoclusters of other noble metals, such as Pt or Au; they are efficient (TOF up to 70 h−1) and easily recoverable by simple extraction of the reaction product from the aqueous phase.Journal of Catalysis 12/2005; 236(2):405–409. · 6.07 Impact Factor