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

A Pd–Ag/SiO2 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/SiO2 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 three-dimensional porous structure was reconstructed from the consecutive cross-sections obtained by this technique. This method shows that the Pd–Ag/SiO2 xerogel catalyst is uniformly dispersed inside the porosity of the alumina foams. Activity and selectivity of Pd–Ag/SiO2 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/SiO2 xerogel catalyst entrapped in porous alumina foams most probably arises from diffusional limitations inside the porous texture of the alumina foams.