%0 Journal Article
%T PVP-Stabilized Palladium Nanoparticles in Silica as Effective Catalysts for Hydrogenation Reactions
%A Caroline Pires Ruas
%A Daiane Kessler Fischer
%A Marcos Alexandre Gelesky
%J Journal of Nanotechnology
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/906740
%X Palladium nanoparticles stabilized by poly (N-vinyl-2-pyrrolidone) (PVP) can be synthesized by corresponding Pd(acac)2 (acac = acetylacetonate) as precursor in methanol at 80¡ãC for 2£¿h followed by reduction with NaBH4 and immobilized onto SiO2 prepared by sol-gel process under acidic conditions (HF or HCl). The PVP/Pd molar ratio is set to 6. The effect of the sol-gel catalyst on the silica morphology and texture and on Pd(0) content was investigated. The catalysts prepared (ca. 2% Pd(0)/SiO2/HF and ca. 0,3% Pd(0)/SiO2/HCl) were characterized by TEM, FAAS, and SEM-EDS. Palladium nanoparticles supported in silica with a size 6.6 ¡À 1.4£¿nm were obtained. The catalytic activity was tested in hydrogenation of alkenes. 1. Introduction Poly (N-vinyl-2-pyrrolidone) stabilized metal nanoparticles have attracted considerable interest when it comes to preventing coagulation and precipitation of the metal nanoparticles. Polymer protecting agents allow preparation of metal colloids that can be stable for months with reasonable control over size as well as shape [1]. The nanoparticles are kinetically unstable with respect to aggregation or the bulk metal and should be stabilized by electrostatic or steric protection [2, 3]. Some of the protecting agents provide steric stabilization such as surfactants [4], ionic liquids [5¨C8], and polyoxoanions [9]. Their main disadvantage, however, is the problematic separation of the catalytic particles from the product and unused reactants at the end of the reaction. Immobilization of the particles on a solid support can facilitate the separation process, but may simultaneously lead to a decrease in activity. The nanoparticle synthesis involves addition of a polymer to the metal salt followed by chemical or thermal reduction to produce a stable black suspension of Pd(0) particles. The types of stabilizers and concentration, the solvent polarity [10], and the aging time of colloidal suspensions [11] can have an effect on the size, shape and catalytic activity of palladium nanoparticles. Platinum nanoparticles protected by PVP have been synthesized by alcohol reduction methods and incorporated into mesoporous SBA-15 silica during hydrothermal synthesis [12]. There have been several very recent reports in the literature of the catalytic properties of nanoparticles of Ag [13, 14], Rh [15], Pt [16, 17] and Pd [18] in PVP. Palladium colloid solutions stabilized by poly(N-vinyl-2-pyrrolidone) can be used as catalysts with high reactivity in C¨CC bond formation microwave-assisted reactions as shown by Heck [19] and Suzuki [20]. Catalytic
%U http://www.hindawi.com/journals/jnt/2013/906740/