Copper-Cobalt Bimetallic Oxides-doped Alumina Hollow Spheres And Its Catalytic Performance For Epoxidation Of Styrene

Catalytic oxidation of styrene is industrially important because the product,styrene oxide?SO?is a multifunctional intermediate for large variety of fine chemicals such as perfumes and drugs etc.The oxidation of olefins by molecular oxygen or other reactive oxygen species,such as H₂O₂ and tert-butyl hydroperoxide?TBHP?,is regarded as a harmless way for olefin oxidation.Nowadays,some heterogeneous catalysts,for example,nano-catalysts and supported catalysts have been used for styrene oxidation.The metal oxide with unique hollow sphere structure is considered as a new kind of promising material.Hollow sphere materials supported metal catalyst exhibited significant catalytic activity in the oxidation reaction,and its activity largely depends on the properties of the active metal and the support.The following three tasks were delineated in this work:Cu-Co bi-component metal oxides hollow-sphere Cu_x Co_yHS?where x,y is Cu/Co molar ratio?were fabricated through the sacrificial carbonaceous template strategy.The dependence of the composition of copper and cobalt on the physiochemical properties and morphologies of Cu_xCo_yHS were characterized by X-ray powder diffraction,scanning electron microscope,transmission electron microscopy and atomic adsorption spectroscopy.Among four Cu_xCo_yHS materials,Cu₇Co₃HS possessed uniform hollow sphere,and well-ordered hollow structure.This catalyst showed comparatively the highest reactivity in the epoxidation of styrene with TBHP as oxidant,showing 60.1%styrene conversion.Copper-cobalt bimetallic oxides-doped alumina hollow spheres Cu_xCo_y/AHS?where x,y is Cu/Co molar ratio?were obtained by the same sacrificial template strategy.Compared with mono metal and other bimetallic catalyst,Cu₇Co₃/AHS catalyst emerged as high performance material,yielding a styrene turnover frequency?TOF?of 21.1 h^–1 and with 93.0%selectivity toward styrene oxide.X-ray Photoelectron Spectroscopy?XPS?spectra for Cu₇Co₃/AHS catalyst revealed the electron transfer is expected to take place from Cu²⁺to Co²⁺.This favored Cu species to combine with TBHP and form Cu-peroxo species.When double bond of nucleophilic olefin as electron donor contact with electrophilic Cu-peroxo group.Actually,XPS spectra for the spend Cu₇Co₃/AHS catalyst evidenced the electron acceptance over copper during the epoxidation.In addition,after four consecutive reactions,87%active copper site and 84%cobalt sites in Cu₇Co₃/AHS catalyst were stable.It is reasonable that the strong interaction of Cu²⁺or Co²⁺and the AHS ensured the stability of the catalyst in the liquid phase reaction.Based on the representative Cu₇Co₃/AHS catalyst,the influence of source?S?and metal?Al?ratio?S/Al=1:1,2:1,4:1,8:1,10:1?on the structure and properties of hollow spheres catalysts was investigated.The ratio of S/Al were decisive in the formation,morphology and pore structure of hollow spheres.The hollow structure could only be produced in the appropriate proportion of S/Al.When the concentration of sucrose was equal to the metal concentration?S/Al=1?,the hollow spheres catalyst was hardly obtained.With the ratio of S/Al increasing,the hollow structure gradually appeared,and the diameter of the hollow spheres decreased from 3.9 to 2.3?m.The optimal yield of styrene oxide?60.1%?was obtained over Cu₇Co₃/AHS?2?catalyst with S/Al=2:1.