Structural Design of Pd/SiO2@Ti-Containing Mesoporous Silica Core–Shell Catalyst for Efficient One-Pot Oxidation Using in Situ Produced H2O2

This study reports the importance of the structural design of heterogeneous catalysts for one-pot reaction. A series of core–shell catalysts were synthesized that consisted of SiO2 core, Pd nanoparticles (NPs), and Ti-containing mesoporous silica (Ti-MS) shell with precise control of the Pd NPs positions, the mesopore diameter, and the thickness of the Ti-MS shell. The catalytic potentials were evaluated for one-pot oxidation reactions involving the direct synthesis of hydrogen peroxide (H2O2) from H2 and O2 gases by the Pd NPs and the subsequent oxidation reaction of sulfide by the isolated TiIV species using in situ produced H2O2 in the mesoporous silica. The precise architecture of the core–shell catalyst significantly enhanced the catalytic performance by a factor of 20, and the catalyst exhibited excellent activity and selectivity toward sulfoxide as compared to the commonly employed Pd-supported/Ti-zeolite (Pd/TS-1) catalyst. This result provides a new perspective of heterogeneous catalysts aimed at developing environmentally benign chemical processes.