Silica aerogels; alternative matrix for catalytic palladium nanoparticles


Effective routes to obtain more valuable products from biomass requires the design of efficient catalysts. Novel catalytic structures are therefore needed to overcome the present challenges. These novel structures require the integration of support active sites in a way that preserves their advantages and capabilities. Here, we introduce novel catalytic structures achieved by the integration of metallic nanoparticles evenly distributed in a mesoporous and high-surface aerogel.

Silica aerogels present amazing properties which make of them suitable materials to overcome these new challenges: high pore volumes, favourable transport properties, stability and surface activity. What is more, their properties can be easily tuned: their textural properties can be tailored by changing the ratios of precursor; the chemistry of their surface can be controlled by using different alkyl-alkoxy/chloro silanes allowing to govern their grade of hydrophobicity; in addition, the option of creating hybrid aerogels make almost all properties requirements achievable.

Pd nanoparticles have been embedded on silica aerogel by using 3 different techniques. In each of them the metal was loaded in the matrix at different steps of the production: the direct synthesis, the wet impregnation and the supercritical (SCI) of the previously dried aerogels. The resultant materials have been characterized by atomic absorption, nitrogen isothermal adsorption-desorption, X-ray diffraction, infrared spectroscopy transmission electron microscopy. In all the techniques the concentration of metal had been tuned by playing with the concentration of the suspension (Pd-PVP nanoparticles used in the direct synthesis) or of the solution of the metallic precursor (palladium acetylacetonate), both in the organic and the supercritical media. The characterization had shown the good distribution of the metallic particles in the matrix, and the negligible effect of the metal on the textural properties. This material was tested in D-glucose hydrogenation, showing a good catalytic response.  The synthesized catalyst is also proposed for the synthesis of methanol/methane from syngas.


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