KIT-6 Supported Cu-Co Oxides And Its Catalytic Performance For Epoxidation Of Styrene

Styrene oxide, an important intermediate of fine chemical, is produced using styrene as raw material through an industrial process with high energy consumption and serious pollution. Recently, research on epoxidation of styrene has been focus on supported metal catalysts employing mesoporous molecular sieves as carriers. KIT-6, a new branch of cubic phase ordered mesoporous material based on silica skeleton, exhibits unique interconnectivity and controllable pore system prepared under hydrothermal conditions, as well as advantages of high surface area, large pore volume and uniform pore size distribution, which existed in traditional molecular sieves, and these unique characters allows KIT-6 to show ranges of application in the field of catalysis. Herein, the catalyst system, which consists of KIT-6 prepared at low hydrothermal temperature as support, and Cu and Co oxides as active species, was investigated in epoxidation of styrene using t-butylhydroperoxide as oxidant at 70 oC. Performance and characterizations of catalysts were discussed to clarify the factors related to activities of the synthesized materials.Catalysts calcinated under different temperature(550 oC and 250 oC, respectively) with disparate catalytic performance were studied. It shows that the activities are attributed to Cu(II) species, while cobaltosic oxide is almost inact. Moreover, catalysts calcinated at 550 oC show better performance, in comparison to the one via calcination under 250 oC. Further study with combination of XRD, N2-sorption, TEM, Raman spectra, XPS and AAS indicates that Cu(II) was embedded in the lattice of Co3O4 when calcinated at 550 oC, and resulted in promotion of catalytic performance. It is verified that the electron structure governs the catalytic behavior of the prepared materials.Catalysts via removal of KIT-6, as well as Cu and Co oxides supported on MCM-41 or SBA-15 were investigated. Catalytic performance dramatically declined when the carrier KIT-6 was removed or replaced by the other two molecular sieves. It further confirmed that KIT-6 is beneficial to maintenance of ordered structure and uniform distribution of active phase with above characterizations. And textural properties are inferred to be an important factor affecting the catalysts activities.The reaction conditions including dosages of oxidant and time were also optimized in the research. Evaluation results shows that increase in either amount of oxidant or reaction time could improve the conversion of styrene, however, the selectivity of styrene oxide decreased. An optimum catalytic property(53.8% conversion of styrene, and 82.6% selectivity of styrene oxide) was obtained using equal amount TBHP as styrene through 8 h. Additionally, a preliminary mechanism for Cu(II) catalyzed epoxidation of styrene in the presence of TBHP was speculated.