Mesostructured dihydroxy-functionalized guanidinium-based polyoxometalate with enhanced heterogeneous catalytic activity in epoxidation

A mesostructured ionic liquid-polyoxometalate (IL-POM) hybrid has been prepared through designing a new dihydroxy-tethered guanidinium-based IL, N′′-(2,3-dihydroxypropyl)-N,N,N′,N′- tetramethylguanidinium chloride, to interact with Keggin-type POM phosphotungstic acid (H₃PW) in a self-assembly process. Scanning electron microscopy and transmission electron microscopy showed its special coral-shaped micromorphology. Nitrogen sorption analysis indicated the formation of a porous structure with a moderate surface area of about 30 m² g^-1 and narrowly distributed pore size located in the mesoscale. Assessed in the cis-cyclooctene epoxidation with H₂O₂, the mesostructured hybrid exhibited superior heterogeneous catalytic activity and steady reusability, and the conversion was more than four times that of homogeneous H₃PW itself, and more than 14 times that of the nonporous analogues. On the basis of the experimental results, a unique "substrate-solvent-catalyst" synergistic mechanism is proposed and discussed for understanding the dramatically enhanced catalytic performance.