Tuned Pd/SiO 2 aerogel catalyst prepared by different synthesis techniques

Abstract

Pd nanoparticles have been embedded on silica aerogel by using three 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 impregnation of the previously dried aerogels. The resultant materials have been characterized to analyze the differences depending on the applied technique for its impregnation. Atomic absorption, nitrogen physisorption, X-ray diffraction, infrared spectroscopy and transmission electron microscopy where performed. In all the techniques the concentration of metal has been varied (from 0.13 to 1.61 % wt.) by modifying the concentration of the suspension (Pd-polyvinylpyrrolidone nanoparticles used in the direct synthesis) or of the solution of the metallic precursor (palladium acetylacetonate), both in the organic solvent and the supercritical media. The characterization had generally shown a good distribution of the metallic particles in the matrix, and the negligible effect of the metal on the textural properties. Finally, considerable variations where observed on the silanol groups on the surface of the catalysts. These materials were tested in D-glucose hydrogenation, observing significant differences on the performance of the catalyst depending on the synthesis technique employed.

Preparation of TiO2-based catalysts with supercritical fluid technology: characterization and photocatalytic activity in CO2reduction

“…The purpose of this work is to assess the use of supercritical fluids in the synthesis of TiO 2 in order to improve catalyst characteristics such as surface, structure, and other physico‐chemical properties, together with its photocatalytic activity in the CO 2 photoreduction process. In this sense, it should be noticed that numerous researchers have synthesized, in supercritical media, catalysts with enhanced properties for several catalytic processes …”

“…In this sense, it should be noticed that numerous researchers have synthesized, in supercritical media, catalysts with enhanced properties for several catalytic processes. 8,25,30,31 In particular, in this work two different titania precursors (titanium tetraisopropoxide, diisopropoxititanium bis(acetyl acetonate)) and two alcohols (ethanol, isopropyl alcohol) have been employed to synthesize the catalysts, CO 2 being the supercritical fluid. Then, the physico-chemical properties of the synthesized catalysts are compared with those of commercial catalyst (Degussa P-25, Evonik), which is usually considered a reference in most studies.…”

Silica Xerogel Obtained by Ultrashort Laser Irradiation of Tetraethyl Orthosilicate

“…In Figure 1, aT EM image of the materials obtainedsoon after their radiation is reported. [7,22] After14 days, the formationo fs olid foam in the irradiated solution was observed. No crystalline structure was observed in the HR-TEM images and the amorphous character of the produced nanostructures has been confirmed by X-ray analysis.…”

“…[4] Several ways to improve the aerogel mechanical properties have been investigated,i no rder to reduce the shrinkage during the supercritical extractiono ft he liquid. [7] The conventional method used to produce silica aerogels is the sol-gelprocess, during which an organic compound containing silicon is involved in ac hemical reactionp roducing silica oxide. [5,6] Since large particles helpt o reduce the capillary forces, the synthesis of primary particles larger than 10 nm seems to be an interesting approach to obtain monolithic silica xerogels.…”

“…[4] Moreover,t he possibility to functionalize the silica backbone with metallicp articles allows to enlarge the aerogel and xerogel functionality beyond their usual applications. [7] The conventional method used to produce silica aerogels is the sol-gelprocess, during which an organic compound containing silicon is involved in ac hemical reactionp roducing silica oxide. [8] In the sol-gelp rocess, different reagents are involved:w ater,s olvents (usually ethanol), complexinga gents and, if necessary,acatalyst.…”