Fractal characterization of wide pore range catalysts:: Application to Pd-Ag/SiO2 xerogels

Fractal analysis has been applied to characterize the structure of Pd-Ag/SiO2 catalysts dried under vacuum (150 degrees C and 12 hPa) with different concentrations of Pd-Ag, Nitrogen adsorption-desorption, mercury porosimetry, and small-angle X-ray scattering measurements have been used. The different approaches to fractal analysis and their conditions of applicability are briefly described. Results are discussed in relation to those derived previously from classical interpretations. This analysis shows that Pd-Ag/SiO2 xerogels exhibit a very open self-similar pore structure analogous to the structure of supercritically dried aerogels and that the micropore texture can be tailored by varying the silver content. (C) 2000 Academic Press.