Xerogels catalytic properties

Structural and catalytic properties of Zr-Ce-Pr-O xerogels S. Rossignol, C. Descorme, C. Kappenstein and D. Duprez... 

The catalytic properties of the aerogel and the xerogel calcined at different temperatures are tested in the n-hexane isomerization in the range 150-220°C. All catalysts are mechanically mixed with Pt/Al203 in the ratio 1/1 (w/w). The presence of platinum is necessary to form the hydrogen species that... 

In general, the structure of sol gel materials evolves sequentially as the product of successive and/or simultaneous hydrolysis and condensation and their reverse reactions (esterification and depolymerization). Thus, in principle, by chemical control of the mechanisms and kinetics of these reactions, namely the catalytic conditions, it is possible to tailor the structure (and properties) of the gels over a wide range. For example, stable silica xerogels of tailored particle dimensions, pore morphology, density and porosity, from relatively... 

The comparison between aerogels and xerogels suggests the importance of the textural properties of this class of solids on their catalytic behaviour. In fact, the interesting... 

Investigation of the sol-gel derived bismuih-molybdcnum-titanium xerogel and aerogel mixed oxide as catalyst for the oxidation of butadiene to furan l 14J 15] indicated activities and selectivities comparable to other suitable catalysts. The unique microstructure and good catalytic performance of the bismuth molybdenum oxide particles are attributed to lilania matrix. How ever, these favorable properties are limited to low temperature reaction conditions since both xerogels and aerogels are prone to rapid restructuring at elevated temperatures, which result in the loss of their unique redox properties. 

Recently, sulfated zirconia aerogels were also doped with cerium. In order to optimize the catalytic performances of these materials, prepared by the sol-gel method, Mejri et al. [48] studied the impact of the solvent evacuation mode on their properties. The xerogel solids (XZC) obtained by ordinary gel drying and calcined at different temperatures exhibit a very low surface areas. On the contrary, the aerogels (AZC) obtained by solvent evacuation under supercritical conditions show a more developed surface areas (Table 6.2). 

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