Hollow titanosilicate nanospheres encapsulating PdAu alloy nanoparticles as reusable high-performance catalysts for a H2O2-mediated one-pot oxidation reaction

Abstract

A tandem reaction combining direct H₂O₂ production from H₂ and O₂ and a subsequent oxidation reaction with H₂O₂ in a single reaction vessel offers an energy-saving and cost-effective oxidation route for the synthesis of targeted chemicals. Herein, we report the synthesis of hollow titanosilicate nanospheres encapsulating Pd and PdAu alloy nanoparticles (NPs) for the H₂O₂-mediated one-pot oxidation reaction. The yolk–shell nanostructured catalyst (Pd@Ti-HMSS), composed of a Pd NP core encapsulated within a hollow mesoporous titanosilicate shell having isolated Ti atoms, is fabricated by a facile etching and re-assembly process using SiO₂ spheres as a template and two different kinds of Si alkoxides as precursors. The synthesized catalyst shows superior catalytic activity in the one-pot oxidation reaction of sulfide under a co-flow of H₂ and O₂, and far outperforms the prototype titanosilicate-supported Pd NP catalysts. Detailed structural characterization and kinetic analysis reveal that the increased catalytic efficiency is attributed to efficient mass transfer of reactants and the associated improved reactivity with in situ generated H₂O₂ over Ti sites. A further enhancement in activity is achievable by encapsulating PdAu alloy NPs, which provide a faster H₂O₂ production rate than monometallic Pd NPs. Owing to the presence of a protective silicate shell, the catalyst shows good stability and reusability over multiple catalytic cycles without significant loss of activity.