Size-Controlled Synthesis of Highly Stable and Active Pd@SiO₂ Core–Shell Nanocatalysts for Hydrogenation of Nitrobenzene

Abstract

Pd@SiO2 core–shell nanoparticles were successfully synthesized by a sol–gel method. Tetradecyl trimethyl ammonium bromide capped Pd nanoparticles were coated with SiO2 through the hydrolysis of tetraethylorthosilicate. The as-synthesized Pd@SiO2 particles consist of Pd cores with a particle size of 3.7 nm and SiO2 shells with a thickness from 10 to 30 nm at different synthetic conditions. The Pd@SiO2 nanocatalysts with 1.9–2.4 nm mesoporous SiO2 shells were generated after removal of tetradecyl trimethyl ammonium bromide from Pd@SiO2 core–shell particles by calcination and following H2 reduction. The relevant characterizations such as XRD, TEM, FT-IR, and BET were carried out for Pd@SiO2 particles, and the results showed that the Pd@SiO2 nanocatalysts were highly stable with the protection of silica shells, and the Pd cores did not increase during thermal treatment and H2 reduction. The studies of catalytic CO oxidation at high temperatures and hydrogenation of nitrobenzene with H2 were tested for Pd@SiO2 nanocatalysts, and the results indicated that Pd@SiO2 nanocatalysts were stable at high temperatures and highly active and stable for hydrogenation of nitrobenzene even after long time use.