Pd–Ag/SiO2 xerogel catalyst forming by impregnation on alumina foams

Abstract

A Pd-Ag/SiO 2 xerogel catalyst prepared in one step by sol-gel process has been entrapped in cylindrical porous alumina foams of three different pore sizes in order to shape the catalyst under the appropriate form with suitable mechanical resistance to be used in an industrial fixed bed reactor. After drying, calcination and reduction, the Pd-Ag/SiO 2 xerogel catalyst pellets are immobilized inside the open porosity of the alumina foam. The localization of the xerogel catalyst in the alumina foams has been studied by X-ray tomography. The threedimensional porous structure was reconstructed from the consecutive cross-sections obtained by this technique. This method shows that the Pd-Ag/SiO 2 xerogel catalyst is uniformly dispersed inside the porosity of the alumina foams. Activity and selectivity of Pd-Ag/SiO 2 xerogel catalyst reference or catalyst entrapped in alumina foams have been studied for selective hydrodechlorination of 1,2-dichloroethane into ethylene. The specific reaction rate obtained with catalyst entrapped in alumina foams is smaller than the one obtained from corresponding catalyst powders. The catalytic activity decrease observed for Pd-Ag/SiO 2 xerogel catalyst entrapped in porous alumina foams most probably arises from diffusional limitations inside the porous texture of the alumina foams.

Carbon xerogels as catalyst supports: Study of mass transfer

“…This morphology does not allow the use of the pseudo‐homogeneous concept for the whole pellet. In a previous study,21, 31 Heinrichs et al developed a model composed of three discrete levels with decreasing sizes in order to describe diffusion in silica xerogels. These levels correspond to: (i) the macroscopic pellet, (ii) an aggregate of silica particles, and (iii) an elementary silica particle.…”

Pressure drop measurements and modeling on SiC foams

“…These peculiars structures are commonly applied for packaging of food, disposable hot-drinks cup (Gibson and Ashby, 1997), packed cryogenic microsphere insulations (Beavers and Sparrow, 1969;Tien and Vafai, 1990;Collishaw and Evans, 1994), solar energy utilization, transpiration cooling (Beavers and Sparrow, 1969), cavity wall insulation, (dwellings, aircraft, submarine cabins, etc. ) and more recently employed as catalyst or structured catalytic supports (Twigg and Richardson, 1994;Groppi and Tronconi, 2000;Richardson et al, 2000;Ismagilov et al, 2001;Twigg and Richardson, 2002;Richardson et al, 2003a,b;Pesant, 2005 Alie et al, 2006;Schimmoeller et al, 2006;Wine et al, 2006;Zamaro et al, 2006). The reason why reticulated ceramic foams are so attractive is the promising of an increase in transport properties (Maestri et al, 2005); the high external surface areas (high porosity respecting an important geometric surface area per volume of solid a c , m 2 /m) lead to high external mass transfer rates.…”

Chemical imaging of catalytic solids with synchrotron radiation

“…42 Similar, although non-SR XMT, studies of note include a study of wetting of alumina spheres and two separate studies into the crystallisation of ZSM-5 and Pd-Ag/SiO 2 xerogels on alumina foams. [43][44][45] However, one subject in particular has received a lot of attention lately: the imaging of transition metal containing catalyst extrudates.…”