One-pot synthesis of molybdenum oxide nanoparticles encapsulated in hollow silica spheres: an efficient and reusable catalyst for epoxidation of olefins

We report a one-pot synthesis of MoO x NPs encapsulated inside hollow silica spheres (MoO x @HSS) which act as an efficient and reusable heterogeneous catalyst in the epoxidation of olefins. A yolk–shell nanostructured MoO x –SiO 2 composite, consisting of core MoO x NPs and permeable porous hollow silica spheres, was fabricated via a self-assembly approach using poly(acrylic acid) as an organic template and dodecyltrimethoxysilane as a pore-directing agent. On the basis of comprehensive structural analyses by FE-SEM, TEM, elemental mapping, N 2 physisorption and Mo K-edge XAFS, we show that MoO x NPs of ca. 5.8 nm diameter are encapsulated within hollow silica spheres having randomly arranged mesopores of ca. 2.1 nm diameter, while addition of an excess amount of the pore-directing agent leads to a deformation of the yolk–shell nanostructures. The obtained yolk–shell nanostructured MoO x –SiO 2 composite exhibits prominent reusability with a modest catalytic activity in the liquid-phase epoxidation of olefins with TBHP owing to the presence of the protective silica shell, making it an effective heterogeneous catalyst for the transformation of olefins into their corresponding epoxides.