Nanosized NiO particles wrapped into uniformly mesocaged silica frameworks as effective catalysts of organic amines

Nanosized NiO-doped cage cubic Pm3n mesoporous silica materials with high Ni/Si contents (∼1) were fabricated via a simple and reproducible one-step synthetic route. Control over the large particle-like monoliths and 3D cage nanostructures was provided by applying an instant preformed liquid crystalline phase of Brij 78 (C₁₈H₃₅(OCH₂CH₂)₂₀OH; C₁₈EO₂₀) surfactant as a template. The solid NiO-silica catalysts were characterized by means of various techniques including XRD, N₂ isotherms, TEM, SEM, XPS and EDX. Results, in general, show the formation of ordered cage NiO-silica matrices even at high amounts of nickel contents to the composition domains. The NiO-supported cage monoliths afforded catalysts that were more active than the free-support NiO and NiO-supported amorphous silicas. The catalytic activity was assessed in the model oxidation reaction of organic amines using batch contact-time experiments over various temperature ranges. Among all catalysts used, the ordered cage catalyst with open, uniform pore architectures, high surface area and large pore volumes allowed efficient adsorption and diffusion of organic amines to the active site of NiO clusters, leading to a high degree of conversion and a high reaction rate. A practically important issue was developing the recyclable catalysts using NiO-doped cage monoliths; however, these catalysts retained their functionalities toward the oxidation of organic amines even after extended regeneration and recycle uses.