Synthesis of Pd nanoparticles on heteropolyacid-supported silica by a photo-assisted deposition method: an active catalyst for the direct synthesis of hydrogen peroxide

A simple and unique methodology to synthesize active Pd nanoparticles using Cs2.5H0.5PW12O40 heteropolyacid-supported silica (CsHPA/SiO2) under UV-light irradiation has been developed. By the photo-assisted deposition (PAD) method, a Pd2+ precursor in aqueous solution can be deposited and easily reduced by the [PW12O40](4-) species generated by photolysis of [PW12O40](3-) species in the presence of (PrOH)-Pr-i as a sacrificial reagent, to afford nanosized Pd-0 metal particles (Pd/CsHPA/SiO2). No direct Pd metal deposition was observed on either pure SiO2 without the CsHPA phase under UV-light irradiation or on CsHPA/SiO2 without UV-light irradiation. The catalytic activity for the direct synthesis of hydrogen peroxide (H2O2) using H-2 and O-2 gases under atmospheric pressure was strongly dependent on the preparation conditions, variation of CsHPA content, and the type of catalyst support. In addition, the Pd/CsHPA/SiO2 catalyst prepared by the PAD method exhibited significantly better activity than the conventionally prepared impregnation catalyst. The Pd surface area from CO adsorption measurements, and also the suppression of undesired side reactions were determined as the crucial factors to achieve efficient catalytic performance.