Abstract
A highly-efficient and stable MgO-supported Co (Co/MgO) catalyst was developed for the oxidation of cyclohexane with oxygen. The effects of the Co loading and support on the catalytic activity of the supported Co3O4 catalyst were investigated. The results show that the Co supported on MgO presented excellent activity and stability. When the Co/MgO catalyst with the Co content of 0.2 wt% (0.2%Co/MgO) was used, 12.5% cyclohexane conversion and 74.7% selectivity to cyclohexanone and cyclohexanol (KA oil) were achieved under the reaction conditions of 0.5 MPa O2 and 140 °C for 4 h. After being repeatedly used 10 times, its catalytic activity was hardly changed. Further research showed that the high catalytic performance of the 0.2%Co/MgO catalyst is attributed to its high oxygen-absorbing ability and the high ratio between the amount of weak and medium base sites with the help of the synergistic interaction between Co and MgO.
Highlights
The aerobic oxidation of cyclohexane is crucial in the chemical industry, because the products of this reaction—cyclohexanol and cyclohexanone—are important feedstock in a variety of reactions [1]
The increase in basicity of the support can accelerate the decomposition of intermediate product cyclohexyl hydroperoxide (CHHP) to cyclohexylperoxy radicals (ROO·)
Co content in the bulk was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES); c
Summary
The aerobic oxidation of cyclohexane is crucial in the chemical industry, because the products of this reaction—cyclohexanol and cyclohexanone (the mixture of the cyclohexanone and the cyclohexanol called KA oil in industry)—are important feedstock in a variety of reactions [1]. It is urgent to develop a new reaction process with a high cyclohexane conversion and high selectivity to KA oil. 15.97% conversion of cyclohexane can be achieved using CrCoAPO-5 molecular sieves with H2 O2 oxidant and acetone solvent at 90 ◦ C [27]. Even though significant progress has been made in the oxidation of cyclohexane with O2 , a high conversion of cyclohexane and high selectivity to KA oil is still a challenge, in which the key problem is to develop a highly efficient catalyst that is environmentally benign, low-cost and with easy separation. Introducing Mn into Co3 O4 to form Mn–Co mixed oxide can markedly enhance the catalytic activity and stability of Co3 O4 , over which 10.4% of cyclohexane conversion and 6.3% of KA oil yield were obtained [36]. Using the hot filtration testing and recycle usage methods, the stability of the 0.2%Co/MgO catalyst was tested, and the results show that after being repeatedly used 10 times, the activity of this catalyst was hardly changed
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