Effect of different treatments on Aerosil silica-supported Pd nanoparticles produced by 'controlled colloidal synthesis'

Pd nanoparticles were prepared by 'controlled colloidal synthesis' (CCS) us ing aerosil silica support. On SiO2, 1-2 nm thick ethanol-rich adsorption l ayer in ethanol-toluene and ethanol-water mixtures was formed into which Pd (II) ions diffused and were reduced there by ethanol. Using Pd(II)-acetate precursor in an ethanol-toluene mixture (sample G1) and PdCl2 precursor in an ethanol-water mixture (sample G2), palladium particles of 7.0 and 8.8 nm size, respectively, were produced, Effects of treatments in air and hydrog en were studied on the Pd/SiO2 samples. The Pd particles showed a twofold/t hreefold increase in the catalytic activity in benzene hydrogenation after treatment in air at 573 K. The activity increase cannot be explained by a c hange in the particle size as indicated by transmission electron microscopy (TEM) and CO chemisorption data. Augmentation of turnover number is interp reted by the removal of carbonaceous residues and by the restructuring of t he surface caused by carbon removal followed by PdO/Pd transition in the su bsequent hydrogen treatment. (C) 2001 Elsevier Science B.V. All rights rese rved.