Journal of Catalysis 221 (2004) 335–346 www.elsevier.com/locate/jcat Synthesis of Pd/SiO 2 , Ag/SiO 2 , and Cu/SiO 2 cogelled xerogel catalysts: study of metal dispersion and catalytic activity Stéphanie Lambert, a Caroline Cellier, b Paul Grange, b Jean-Paul Pirard, a and Benoît Heinrichs a,∗ a Laboratoire de Génie Chimique, B6a, Université de Liège, B-4000 Liège, Belgium b Unité de Catalyse et chimie des matériaux divisés, Université Catholique de Louvain, B-1348 Louvain-La-Neuve, Belgium Received 23 May 2003; revised 22 July 2003; accepted 22 July 2003 Abstract Pd/SiO 2 , Ag/SiO 2 , and Cu/SiO 2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Pd, Ag, and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). It appears that the metal complex acts as a nucleation agent in the formation of silica particles. The resulting catalysts are then composed of completely accessible metallic crystallites with a diameter of about 3 nm located inside silica particles exhibiting a monodisperse microporous distribution. The metal dispersion has been determined from CO and O 2 chemisorption, TEM, and X-ray diffraction. Although metallic particles are located inside silica particles, their complete accessibility, via the micropore network, has been shown. 1,2-Dichloroethane hydrodechlorination over Pd/SiO 2 catalysts mainly produces ethane and the specific hydrodechlorination rate per gram of Pd decreases when metal loading increases. Hydrodechlorination over Pd/SiO 2 catalysts is a structure-insensitive reaction with regard to the ensemble size concept. Benzene oxidation over Ag/SiO 2 and Cu/SiO 2 catalysts produces H 2 O and CO 2 only and specific oxidation rate per gram of metal decreases when silver and copper loadings increase. Furthermore, it is concluded that benzene oxidation is a structure-insensitive reaction.  2003 Elsevier Inc. All rights reserved. Keywords: Cogelled xerogel catalysts; Nucleation; Metal dispersion; Hydrodechlorination; Oxidation 1. Introduction A high activity of a supported catalyst often calls for a large active surface area and, thus, for small particles, i.e., a high dispersion of the active phase. Because small metal particles tend to sinter already at relatively low temperatures, these generally are applied into a support material which it- self is thermally stable and maintains a high specific surface area up to high temperatures [1]. With a support like sil- ica, other important physical features like texture (specific surface area, pore size distribution, and porous volume), den- sity, and mechanical strength can be established. The sol–gel method was used by several authors in or- der to obtain monometallic catalyst particles finely dispersed on a mineral support. Schubert and co-workers developed a particularly interesting method to homogeneously disperse nanometer-sized metal particles in a silica matrix [2–5]. These authors used alkoxides of the type (RO) 3 Si–X–A in * Corresponding author. E-mail address: b.heinrichs@ulg.ac.be (B. Heinrichs). which a functional organic group A, able to form a chelate with a cation of a metal such as palladium, silver, cop- per, nickel, etc. is linked to the hydrolyzable silyl group (RO) 3 Si–via an inert and hydrolytically stable spacer X. The cocondensation of such molecules with a network-forming reagent such as TEOS, Si(OC 2 H 5 ) 4 , results in materials in which the metal is anchored to the SiO 2 matrix. Heinrichs et al. used this cogelation method for the preparation of Pd/SiO 2 aerogel catalysts [6]. In this study, (RO) 3 Si–X–A = 3-(2-aminoethylamino)propyltrimethoxy- silane, NH 2 –CH 2 –CH 2 –NH–(CH 2 ) 3 –Si(OCH 3 ) 3 = EDAS, and the Pd precursor is Pd acetylacetonate, Pd[CH 3 COCH =C(O–)CH 3 ] 2 = Pd(acac) 2 . It has been shown that the Pd 2+ complex, Pd 2+ [NH 2 –CH 2 –CH 2 –NH–(CH 2 ) 3 –Si(OCH 3 ) 3 ] 2 , acts as a nucleation agent in the formation of silica par- ticles. The resulting catalysts are composed of completely accessible palladium crystallites located inside silica parti- cles. It was shown that these samples are sinterproof during hypercritical drying due to the fact that Pd crystallites can- not migrate because they are trapped inside the microporous SiO 2 particles. In such catalysts, in order to reach active 0021-9517/$ – see front matter  2003 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2003.07.014