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Formation and structural characteristics of Pd–Ag/SiO2 and Pd–Cu/SiO2 catalysts synthesized by cogelation

“…2), it appears that Pd-Ag/SiO 2 and Pd-Cu/SiO 2 cogelled xerogel catalysts are composed of silica particles arranged in strings or aggregates, and although TEM gives only a 2D view, it seems that small metal particles are located inside silica particles, whereas large metal are located at their surface. This silica matrix structure and this metal particlesÕ localization were also observed in previous studies [7,14,15,23] in the case of monometallic Pd/SiO 2 , Ag/ SiO 2 , Cu/SiO 2 and bimetallic Pd-Ag/SiO 2 cogelled aerogel and xerogel catalysts.…”

“…In the case of Pd/SiO 2 , Ag/SiO 2 and Cu/SiO 2 cogelled aerogel and xerogel catalysts synthesized by Lambert et al [14,15,30] and Heinrichs et al [23], it was suggested that this localization of the metal inside the silica matrix was induced by a nucleation process initiated by the ligand of the metal, namely EDAS. Nucleation by EDAS was verified by Alié et al in xerogels without metal [21].…”

“…Furthermore, 17 O NMR spectroscopy and rheological measurements showed that the hydrolysis-condensation of EDAS is much faster than that of TEOS [31,32]. So hydrolyzed EDAS molecules can act as a nucleation agent leading to silica particles with a hydrolyzed EDAS core (where is located the metal in Pd/SiO 2 , Ag/SiO 2 and Cu/SiO 2 aerogel and xerogel catalysts [14,15,23,30]) and a shell principally made of hydrolyzed TEOS.…”

“…The cogelation solgel process proposed by Schubert [13] allows obtaining monometallic nanometer-sized particles finely dispersed on a mineral support. Heinrichs et al [7] and Lambert et al [14,15] used this process to synthesize Pd/SiO 2 , Ag/ SiO 2 , Cu/SiO 2 and Pd-Ag/SiO 2 xerogel catalysts. This method consists in using alkoxides of the type (RO) 3 Si-X-A, in which a functional organic group A, able to form a chelate with a cation of a metal such as palladium, silver, copper, etc., is linked to the hydrolysable silyl group (RO) 3 Si-via an inert and hydrolytically stable spacer X.…”

Preparation and characterization of xerogel catalyst microspheres

“…This problem was solved by Heinrichs et al [3][4][5][6] and Lambert et al [7] who succeeded in synthesizing Pd/SiO 2 , Ag/SiO 2 , Cu/SiO 2 , and Pd-Ag/SiO 2 catalysts by co-gelation of TEOS with 3-(2-aminoethylamino)propyl-trimethoxysilane (EDAS) as ligand for Pd and Cu, and 3-aminopropyltriethoxysilane (AES) for Ag, using Pd(acac) 2 nanometer-sized metal particles were located in the center of the silica particles. It was shown [5,8] that the palladium-EDAS complex acted as a nucleation agent in the formation of silica particles because of the presence of methoxy groups on EDAS, which are more reactive than the ethoxy groups of TEOS [9][10][11][12]. Another interesting property of these xerogel catalysts is their low density, despite drying under vacuum: densities as low as 0.15 g/cm 3 have been obtained [6].…”