Synthesis Of Highly Dispersed Supported CuO Based Catalysts For Epoxidation Of Styrene

Styrene oxide(SO)is an important intermediate of organic synthesis and raw materials,which has been widely used in the field of pharmaceutical synthesis,organic synthesis,perfume processing.In recent years,with the rapid development of fine chemical industry in China,the application of SO is widened and the demand is increasing year by year.The catalytic epoxidation of styrene is the main method for the preparation of styrene oxide.Currently,using halogen oxide as oxidant in homogeneous system has achieved high catalytic performance for styrene epoxidation in the industry.However,halogen oxide is strong corrosive to reaction device,and the ratio of oxidant and substrate should be strictly measured in the preparation process.In addition,large amounts of wastewater containing halogen will be produced in the process,resulting in the severe environmental problem.Therefore,the development of environmental friendly synthesis technology of SO is of great importance.Heterogeneous catalysis is one of the most green and efficient methods for the preparation of SO.The supported noble metal such as Au and Ag catalysts have showed favorable catalytic activity and selectivity in the epoxidation of styrene.However,precious metal are scarce and expensive,which inhibites their maximum application.Therefore,the ongoing search for new non-noble catalysts with excellent catalytic performance for styrene epoxidation in the environmentally friendly heterogeneous catalytic system has aroused great interest.Copper oxide(CuO)was reported to catalyze the selective epoxidation of styrene because that CuO could adsorb with styrene strongly and activate the oxidant effectively.For the CuO based catalyst,the maximum exposure of the surface active center is particularly important for catalytic performance in the epoxidation reaction.However,the traditional preparation methods and processing methods have limitations on the improvement of the active center dispersion.Furthermore,developing a new supported CuO catalysts with highly dispersed active center is urgent to realize the green and efficient synthesis of SO.In this paper,a series of supported CuO catalysts were prepared by precipitation-deposition method.The experimental results showed that the dispersion of CuO and the surface area of Cu had important influence on conversion of styrene and selectivity of SO.Due to the largest surface area of Cu and highest dispersion of CuO,CuO/CoAl-LDH catalyst showed the highest catalytic performance(98.83%styrene conversion and 72.03%SO selectivity).The structure-performance relationship study showed that the acidity and basicity of support has significant effect on CuO dispersion and Cu surface area.Compared with the inert and acidic support,the support with the basic center on the surface was more advantageous to promote the dispersion of CuO.Moreover,the results also showed that CoAl-LDH support could further improve the dispersion of CuO due to the synergytic effect of acid-base centers,leading to the improvement of the epoxidation performance.The reaction mechanism of styrene epoxidation was studied in the CuO/CoAl-HT catalytic system,which indicated that the active sites of catalyst was copper(?)ion in CuO.During reaction,the copper(II)ion could be coordinated with oxygen free radicals produced by the activated TBHP to form Cu?-peroxo.The Cu?-peroxo species was beneficial to the epoxidation of styrene.Furthermore,CuO/CoAl-LDH catalysts were be synthesized by the deposition-precipitation method(DP),oil amine method and sol-gel method.Epoxidation of styrene results showed that the catalytic performance of CuO/CoAl-LDHDP catalyst was the best among the obtained CuO/CoAl-LDH catalysts.The H2-N2O titration results showed that the catalyst prepared by DP method had the highest dispersion of CuO and the largest surface area of Cu.Based on the DP method,Ce was used to modify the CuO/CoAl-LDH catalyst.The catalytic performance results showed that the CuO-CeO/CoAl-LDH catalyst possessed the highest catalytic performance(99.56%styrene conversion and 79.08%SO selectivity)when the Ce/Cu molar ratio was 0.2.The structure-performance relationship results showed that the Ce modification promoted the amounts of copper(II)species in CuO on the surface of catalyst,which was beneficial to improve the selectivity of SO.