(171g) Selective Oxidation of Ethylbenzene Catalyzed By N-Hydrophthalimide and ZSM-5 Supported Co(II), Mn(II), Cu(II), Zn(II), Fe(III) with Molecular Oxygen Under Mild Conditions

A commercial ZSM-5 type zeolite (Nankai University) was  ion-exchanged  with  aqueous  solutions  of  metal salts to obtain transition metals containing ZSM-5 catalysts (M-ZSM-5, M= Co(II), Mn(II), Cu(II), Zn(II), Fe(III)). The catalysts were characterized by X-ray diffraction (XRD), BET, scanning electron micrograph (SEM), transmission electron microscopy (TEM) and ICP-AES. The XRD patterns of M-ZSM-5 showed no obvious change of characteristic peaks compared to those of parent ZSM-5, but with some decreased intensities, which indicated that the ion-exchange treatment did not destroy the original structure of parent ZSM-5 zeolite. The BET surface areas and pore sizes of various M-ZSM-5 zeolites exhibited a slight decrease according with the BET results due to the metal ion exchange. The SEM images showed that there was no significant difference in surface morphology between M-ZSM-5 and ZSM-5 but with a few particle aggregation as can be seen in TEM images. The metal contents were also determinated by ICP-AES. The catalytic activity of various M-ZSM-5 catalysts was investigated by combining with N-hydroxyphthalimide (NHPI) for the selective oxidation of ethylbenzene with dioxygen under mild conditions. The oxidation results showed that all five M-ZSM-5 catalysts exhibited excellent activity on oxidation of ethylbenzene in the presence of NHPI with good conversion of ethylbenzene and high selectivity to product acetophenone. Among various M-ZSM-5 catalysts, the decreasing order of the relative catalytic activity was: Co(II)-ZSM-5 > Mn(II)-ZSM-5 > Zn(II)-ZSM-5 > Fe(III)-ZSM-5 > Ni(II)-ZSM-5, which probably due to the ability of accepting electron during the formation of oxo-transition metal reactive intermediate. The leaching and recycling tests showed that M-ZSM-5 was stable in the reaction and could be reused. Based on the literature, a plausible radical mechanism for the oxidation reaction was also proposed.