Keggin-type polyoxometalate-based supramolecular complex for selective oxidation of styrene to benzaldehyde

Abstract

A Keggin-type polyoxometalate (POM)-based supramolecular complex with the formula of [Co(H₂O)₃]₂(ttb)₂[HBW₁₂O₄₀]·2H₂O (1) (ttb = 1,3,5-tri(1,2,4-triazol-1-ylmethyl)-2,4,6-trimethylbenzene) was synthesized via hydrothermal method and characterized by single-crystal X-ray diffraction, IR and powder X-ray diffraction analyses. In 1, [Co(H₂O)₃]²⁺ cations are connected with the adjacent ttb ligands to form a porous two-dimensional (2-D) cationic layered network, and the [HBW₁₂O₄₀]⁴⁻ polyoxoanions are encapsulated between the layers through intermolecular interactions, generating a POM-capsulated 3-D supramolecular network. Integrating the advantage of Co²⁺ with [HBW₁₂O₄₀]⁴⁻, 1 as a heterogeneous catalyst displays a synergistically improved catalytic performance for oxidation of styrene. It can achieve almost 98% conversion of styrene in 4 h with about 99% selectivity of benzaldehyde product, which is about five times more than the catalytic activities of the single components (Co(OAc)₂·4H₂O or K₅BW₁₂O₄₀). A series of comparative analyses showed that the high catalytic performance of 1 is mainly attributed to the synergistic effect of unsaturated metal sites and polyoxoanions. This work provides an approach for developing highly efficient POM-based heterogeneous catalysts toward the selective oxidation of styrene.

Graphical Abstract

Keywords:

• Polyoxometalate
• supramolecular complex
• heterogeneous catalysis
• styrene oxidation

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was financially supported by the Natural Science Foundation of China (grants 21901060 and 21871076), the Natural Science Foundation of Hebei Province (grants B2020205008, B2016205051 and B2019205074), the Natural Science Foundation of Hebei Education Department (grant BJ2020037) and the Opening Project of Key Laboratory of Polyoxometalate Science of Ministry of Education and the College Students' Innovative Entrepreneurial Training Plan Program of Hebei Normal University (grant 201910094087).