Palladium core–porous silica shell-nanoparticles for catalyzing the hydrogenation of 4-carboxybenzaldehyde

Pd@SiO2 core–shell-particles were prepared by coating silica onto the surface of Pd–polyvinylpyrrolidone (PVP) colloids, according to the Stober method. These particles were characterized with SEM, TEM, nitrogen adsorption/desorption, XRD, CO chemisorption, and were used to catalyze the hydrogenation of 4-carboxybenzaldehyde (4-CBA) to p-toluic acid (PT). The maximum PT yield (around 99%) occurred at 160–175 °C, which was much lower than the temperature (250–270 °C) used in the commercial terephthalic acid refining process (with a Pd/C catalyst).