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Highly porous nanocomposite aerogels based on bimetallic Fe and Mo nanoparticles with a variable Fe:Mo weight ratio ranging from 5:1; 3:1; and 0.7:1 dispersed on amorphous silica were obtained. N physisorption, X-ray diffraction, and transmission electron microscopy indicate that the Fe/Mo-SiO nanocomposite aerogels as obtained by a co-gelation sol-gel route followed by supercritical drying and reduction treatment under H exhibit Fe and Mo nanocrystals with size in the range 4-10 and 15 nm, respectively, supported on highly porous silica. The catalytic performance of the Fe/Mo-SiO aerogels for the synthesis of multi wall carbon nanotubes (MWCNT) by catalytic chemical vapour deposition (CCVD) was evaluated in terms of amount and quality of the produced CNTs as assessed by gravimetric results, thermal analysis, and TEM. The effect of catalyst composition and CCVD temperature was investigated, pointing out that high reaction temperatures (800 °C) favor the formation of MWCNTs with high quality in elevated yield, the highest C uptake value being >400 %. Catalyst composition and CCVD temperature were also found to affect the homogeneity of CNT morphology, the best MWCNT quality (with outer diameter 23-25 nm) being achieved at 800 °C with the catalyst having the largest Mo content. [ABSTRACT FROM AUTHOR]

In this work, nanocomposites constituted of FeCo alloy nanoparticles dispersed on a highly porous silica aerogel have been designed as catalysts for low temperature Fischer-Tropsch synthesis. The catalysts were characterized by XRD, TEM, N physisorption and SEM analysis. A high catalytic activity with CO conversions up to 95 % has been obtained, with enhanced selectivity for the C-C hydrocarbons. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Porous nanocomposites made out of nickel dispersed on silica or alumina matrices were prepared as prospective catalysts for the nitroxidation of hydrocarbons in the form of aerogel or xerogel by adopting either a supercritical or a conventional gel drying procedure. The structural and textural features of the materials were investigated by X-ray diffraction, transmission electron microscopy and N physisorption and combined to the acid/base and reducibility data as deduced by adsorption microcalorimetry and temperature programmed reduction (TPR) profiles. The alumina-based samples are made out of nanocrystalline nickel aluminate and are mesoporous, although the aerogel has larger pore volumes and surface area than the xerogel. On the other hand, in the silica-based samples nickel oxide nanocrystals are dispersed on amorphous silica, the size of the nanocrystals being around 5 nm in the microporous xerogel and 14 nm in the mainly mesoporous aerogel. TPR data point out that the alumina-based samples have similar reducibility, whereas significant differences were observed in the silica-supported composites, the NiO-SiO aerogel exhibiting improved reducibility at low temperature. The NO-catalyst interaction was monitored by temperature programmed NO reaction coupled to mass spectrometry and preliminary tests on the use of the NiO-SiO xerogel and aerogel nanocomposites for the catalytic nitroxidation of 1-methyl-naphthalene to 1-naphthonitrile were obtained in a fixed-bed continuous-flow reactor. The data indicate that the aerogel exhibits larger selectivity than the corresponding xerogel, pointing out the importance of tuning the sol-gel parameters in the design of porous composite materials for catalytic applications. [ABSTRACT FROM AUTHOR]

series of novel nanocomposites constituted of FeCo nanoparticles dispersed in an ordered cubic Im3m mesoporous silica matrix (SBA-16) have been successfully synthesized using the wet impregnation method. SBA-16, prepared using the non-ionic Pluronic 127 triblock copolymer as a structure-directing agent, is an excellent support for catalytic nanoparticles because of its peculiar three-dimensional cage-like structure, high surface area, thick walls, and high thermal stability. Low-angle X-ray diffraction, N physisorption, and transmission electron microscopy analyses show that after metal loading, calcination at 500 °C, and reduction in H flux at 800 °C, the nanocomposites retain the well-ordered structure of the matrix with cubic symmetry of pores. FeCo alloy nanoparticles with spherical shape and narrow size distribution (4-8 nm) are homogeneoulsy distributed throughout the matrix and they seem in a large extent to be allocated inside the pores. [ABSTRACT FROM AUTHOR]

Nanocrystalline γ-Al2O3 and FeCo-Al2O3 nanocomposites containing FeCo alloy nanoparticles well dispersed in the nanocrystalline γ-Al2O3 matrix were successfully obtained by the sol-gel method using aluminum tri-sec-butoxide and iron and cobalt nitrates as precursors. The gels were submitted to high temperature supercritical drying which allowed to obtain aerogels with high surface areas and pore volumes. [ABSTRACT FROM AUTHOR]