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Over the last years, mesoporous silicas have gathered considerable interest especially in the field of catalysis, singled out as excellent catalytic supports owing to their intriguing textural features. Herein, the synthesis of novel nanoporous silicate materials containing copper or palladium nanoparticles, by means of co-assembly and one-pot templating pathways is described. Inclusion of metal nanoparticles within the porous network of the silicate materials is accomplished with the use of hyperbranched Polyethyleneimines (PEIs), serving both as chelating and secondary structure directing agents. The co-assembly method involves the introduction of PEI into the initial reaction mixture containing the triblock copolymer Pluronic P123 as the main template and TEOS as the silica source, whereas incorporation of metal nanoparticles is performed at a second step. The one-pot approach, achieves metal loading in a single step through the direct insertion of PEI already complexed with the desired metal, into the synthetic gel. Several parameters are investigated including solution's pH, reaction path and PEI's molecular weight. Results from TGA, XRD, N 2 porosimetry, electron microprobe, SEM, TEM and UV-DR analyses, confirm that both synthetic strategies can produce nanoporous materials with advanced and tunable textural and morphological characteristics and thus widened application prospects. Among the examined synthesis parameters, PEI molecular weight and synthetic gel's pH were found to have the most pronounced effect on final material pore architecture, morphology, metal loading and dispersion. Preliminary deNO x activity tests in the NO + CO reaction indicated that the developed materials could find use in environmental applications.

Abstract:Copper containing silica nanostructures are easily produced through a low cost versatile approach by means of hyperbranched polyethyleneimine (PEI), a water soluble dendritic polymer. This dendritic molecule enables the formation of hybrid organic/inorganic silica nanoparticles in buffered aqueous media, at room temperature and neutral pH, through a biomimetic silicification process. Furthermore, the derived hybrid organic/inorganic materials dispersed in water can be easily loaded with various copper amounts, due to the presence of PEI, which, despite having been integrated in the silica network, retains its strong copper chelating ability. Following calcination, the obtained copper loaded nanopowders are characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), N 2 adsorption, Temperature programmed reduction (TPR) and UV-Vis diffuse reflectance (UV-Vis-DR) techniques and evaluated for automotive exhaust purification under simulated conditions at the stoichiometric point. Effective control over final materials' pore structural and morphological characteristics is provided by employing different buffer solutions, i.e., tris(hydroxymethyl)aminomethane (Tris) or phosphate buffer. It was found that the enhancement of the nanopowders textural features, obtained in the presence of Tris buffer, had a great impact on the material's catalytic behavior, improving significantly its activity towards pollutants oxidation.

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