环己烷绿色氧化合成环己醇/环己酮(KA油)催化剂及机理研究进展

Progress on the catalysts for green oxidation of cyclohexane to cyclohexanol/one(KA oil) and the reaction mechanism studies

环己烷绿色氧化合成环己醇/酮(KA油)一直是饱和C—H氧化领域的研究热点。本文综述了近十年来过氧化氢环己烷氧化和分子氧液相环己烷氧化的催化研究情况,指出过氧化氢环己烷氧化反应虽然条件温和、环己烷转化率和KA油选择性高,但活性较高的反应体系一般为包含昂贵配合物、酸、溶剂和氧化剂的复杂均相体系,不利于产物和催化剂分离,同时过氧化氢利用率较低,氧化剂成本高。液相分子氧环己烷氧化采用多相催化剂,操作简单,其中金和纳米氧化物有望成为潜在的工业催化剂。对环己烷氧化机理成果进行分析,指出除了金属卟啉的氧异裂非自由基机理,环己烷氧化按自由基机理进行,为自催化反应,但催化剂可促进活性自由基产生,活化C—H键,提高反应速率。最后指出开发有潜力的环己烷氧化多相催化剂和探索反应机理是今后的研究方向。

Because of its industrial importance,green oxidation of cyclohexane to cyclohexanol/one（KA oil） has become a research hotspot in the field of saturated C—H oxidation. The catalytic research results on peroxidative oxidation of cyclohexane and liquid-phase oxidation of cyclohexane with molecular oxygen in past decade have been reviewed in this paper. It is concluded that peroxidative process can be conducted under mild reaction conditions and with high conversion of cyclohexane and selectivity for KA oil,but the catalyst and products are very difficult to separate for the complex homogeneous mixture containing expensive complex,acid,solvent and oxidant. In addition,the low utilization efficiency of H2O2 results in high cost of the oxidant. Alternatively,liquid-phase oxidation of cyclohexane with molecular oxygen and heterogeneous catalyst is easy to conduct. Catalysts of gold and nano-metal oxides are expected to find industrial applications. The analysis of the reaction mechanism indicates that cyclohexane oxidation follows a radical mechanism,which is different from the oxygen bond heterolytic cracking mechanism of metal porphyrin catalysts. The reaction is of auto-oxidation,but the employment of catalyst can accelerate the generation of active radicals,activate the C—H bond and enhance the reaction rate. In summary,the development of potential heterogeneous catalysts for cyclohexane oxidation and investigation of its reaction mechanism are considered as directions for future research.