The cascade catalysis of core-shell CoW-MOF: Further intensified allylic oxidation of cyclohexene to 2-cyclohexene-1-one

Abstract

The low selectivity of cyclohexene allylic oxidation products (2-cyclohexene-1-one and 2-cyclohexene-1-ol) is the main barrier hindering the industrialization process of the cyclohexene allylic oxidation reaction. Improving the selectivity of 2-cyclohexene-1-one through cascade catalysis is an innovative strategy for the preparation of a single-target product from cyclohexene. In this paper, based on the “dissolution-regeneration” process, the Co-based metal-organic framework ZIF-67 was reconstructed using Na₂WO₄·4H₂O (as the W sources). a series of core-shell nanostructured catalysts (Co_xW_y-MOF) composed of a ZIF-67 core and a CoWO₄ shell layer were obtained. These catalysts have a specific surface area one order of magnitude higher than that of the porous CoWO₄ composite oxide. Thus, the significantly abundant active Co and W sites were evenly dispersed on such a high specific surface area for the cyclohexene allylic cascade reaction to generate 2-cyclohexene-1-one. Compared with porous CoWO₄ composite oxide, the conversion rate of Co_0.5W_0.5-MOF catalyst to cyclohexene increased by 9.8 %, and the value was 87.6 %. The selectivity for 2-cyclohexene-1-one is increased by 12.5 %, and the value was 83.3 %. Moreover, it can maintain its catalytic performance after five catalytic cycles of repeated use. The reasons for further intensified the cyclohexene allylic cascade oxidation mechanism are the full exposure of the active sites in the CoWO₄ shell layer and the synergistic catalytic effect between the ZIF-67 core and the CoWO₄ shell layer. The new material of CoWO₄ surface reconstruction based on the ZIF-67 precursor is an efficient catalyst for the cyclohexene allylic oxidation to produce 2-cyclohexene-1-one.