Facile and surfactant-free synthesis of supported Pd nanoparticles on hydrotalcite for oxidation of benzyl alcohol

Abstract

We report a facile modified deposition–precipitation method that permits reproducible preparation of a supported Pd catalyst with small particle size and narrow size distribution but without the protection of a surfactant and any additional treatment. The pH value in this technique plays a key role in controlling the size of the Pd nanoparticles as well as the electronic environment of the surface Pd atoms. With the increasing pH (4.0–12.0), the average size of the Pd nanoparticles decreases gradually, meanwhile, the peak area ratio for CO adsorbed on bridge-bonded Pd to that adsorbed on threefold-coordinate Pd increases. Stronger support–metal interaction (electron transfer from Pd⁰ to support) is observed at pH values of 7.0 and 10.0. Both the small particle size and the electron-deficient surface metallic Pd contribute to enhancement in the activity for the solvent-free oxidation of benzyl alcohol. Therefore, compared with supported Pd catalysts prepared by sol immobilization, impregnation and deposition–precipitation methods, Pd/hydrotalcite synthesized by this modified deposition–precipitation approach shows a higher TOF value (5330 h⁻¹). This enhanced catalytic performance can also be maintained in five cycles. Under the considerations of green chemistry, a number of Pd catalysts were then prepared on alternative supports using this method without the addition of alkali in the preparation process.