Supported Nanopowders

Ruthenium catalysts, supported on a commercial alumina (surface area 155 m have been prepared using two different precursors RUCI3 and Ru(acac)3 [172,173]. Ultrasound is used during the reduction step performed with hydrazine or formaldehyde at 70 °C. The ultrasonic power (30 W cm ) was chosen to minimise the destructive effects on the support (loss of morphological structure, change of phase). Palladium catalysts have been supported both on alumina and on active carbon [174,175]. Tab. 3.6 lists the dispersion data provided by hydrogen chemisorption measurements of a series of Pd catalysts supported on alumina. is the ratio between the surface atoms accessible to the chemisorbed probe gas (Hj) and the total number of catalytic atoms on the support. An increase in the dispersion value is observed in all the sonicated samples but the effect is more pronounced for low metal loading. 

Leighton, The Acoustic Bubble, Academic Press, London, 1994. 

Reisse, and K.S. Suslick (ed.), Sonochemistry and Sonoluminescence, NATO ASI Series, Kluwer Academic Publishers, 1999. 

Suslick (ed.). Ultrasound, its Chemical, Physical and Biological Effects, VCH, Wein-heim, 1988. 

Mason and J.P. Lorimer, Sonochemistry, Theory, Applications and Uses of Ultrasound in Chemistry, Ellis Horwood Publishers, 1989. 

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Authors are grateful to MIUR for financial support, PRIN 2001-2003 "Synthesis of nanopowders under microwave irradiation". 

Li et al. [498] reported preparation of ri02/zeolite from precursors of Ti(OC4Hg)4 and natural zeolite, clinoptilolite. The researchers indicated that the synthesized rj02/zeolite displays higher photocatalytic activity than pure Ti02 nanopowders in degradation of methyl orange. The reason of this observation was concluded to he due to the super adsorption capability of the zeolite support. 

Several companies and research labs around the world have applied the FG process with the support of PowderPro. Typical ceramic powders are oxides (AI2O3, Zr02, and Si02), nitrides (Si3N4), and carbides (SiC), but also nanopowders, diamonds, and pharmaceuticals like proteins and enzymes. 

The XRD pattern shows an enhanced homogeneity in metal alkoxide. The pattern of diffraction peaks is the same for all metal alkoxide and corresponds to the related peaks. On calcinations the broadness of diffraction peaks reduces, thereby supporting the formation of crystalline nanopowder of bimetallic oxide with correct phase, and with favourable microstructural properties. 

The effect of the aluminum oxide layer is also known to reduce the propagation of thermite reactions since alumina is an effective absorber of thermal energy. A study by Weismiller et al. of a 49 % active aluminum nanopowder in a thermite with copper oxide supports the idea that too much oxide can actually reduce thermite performance. Table 13.4 shows Weismiller s data which indicates the negative effect of a thick oxide layer on aluminum nanoparticles. 

Interest in the synthesis of monodispersed oxide nanopowders increased essentially in the past few years due to their specific properties such as chemical, thermal, electrical, optical, mechanical, magnetic, and morphological properties [2,3]. Such properties recommend the oxide nanopowders for applications in very different areas such as pigments, catalysts, supports in chromatography, or as raw materials for the preparation of advanced polycrystalline ceramics [4-6]. 

All chemicals and materials were used as received without further purification. All solutions were prepared from methanol (>99.9%, Aldrich) or KOH (>85%, Aldrich) with deionized water (18.2 MQ cm). Unsupvported electrocatalysts were used in voltammetric and chronoamperometric measurements, including Pt black (Alfa, S.A. typically 27 m g-i), Pd black (Alfa, S.A. typically 20 m g-i) and Ag nanopowder (Alfa, 20-40 nm). Carbon supported Pt (Fuel Cell Store, 60 wt% Pt/C) and carbon supported Pd (Sigma-Aldrich, 30... 

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