Core-shell-structured titanosilicate as a robust catalyst for cyclohexanone ammoximation

Core-shell-structured MWW-type titanosilicate (Ti-MWW) with a well-defined micro-meso hierarchical porosity was fabricated by using self-assembly technique. This composite material Ti-MWW@meso-SiO₂ was applied as the catalyst for the ammoximation of cyclohexanone in a continuous slurry reactor. The combination of characterizations, such as XRD, SEM, HR-TEM, and N₂ adsorption, verified that the composite material was composed of zeolite crystallites as core and mesosilica as shell and that the micropores and mesopores were penetrated well with each other, which significantly facilitated the diffusion of large molecules. In continuous ammoximation of cyclohexanone as a probe reaction, the composite exhibited significantly prolonged lifetime in comparison to the parent Ti- MWW catalyst and the physical mixture of Ti-MWW and mesosilica. The unique catalytic behaviors of Ti-MWW@meso-SiO₂ were ascribed to protecting effect of the mesosilica shell. It served as a sacrificial lamb that protected the active component of zeolite core against rapid desilication and coke formation, leading to a stable duration of the catalysts.