NiCr- and NiAl-Oxides Catalysts for Oxidation of Ethylbenzene

Abstract

NiCr- and NiAl- layered double hydroxide (LDH) precursors were synthesized and calcined tometal oxides. They were characterized by chemical analysis, X-ray diffraction, Fourier transform infraredspectroscopy and surface area (BET) measurement. Their catalytic activity was tested in the selectiveoxidation of selective ethylbenzene to acetophenone using tert-butylhydroperoxide as an oxidant. Theinfluence of various reaction parameters: type of metal, oxidant/ethylbenzene molar ratio and catalystamount on the activity and selectivity for the oxidation reaction were evaluated. Experimental results showthat under the reaction condition of 0.2 g catalyst, TBHP/ethylbenzene molar ratio = 3, temperature at130 °C and reaction time 12 h, the NiCr-oxide and the NiAl-oxide show high conversion ofethylbenzene (75 and 77%), compared to that from the MgAl-oxide (50%). The NiAl-oxide shows muchhigher selectivity for acetophenone (98%) than the NiCr-oxide (75%). Redox metal species plays therole as the active centers in the oxidation process. Higher conversion can be obtained when the catalystamount was increased. A reaction mechanism was proved to be partly via free radicals. Moreover theheterogeneous catalysts are reusable.

Keywords : Ethylbenzene / Oxidation/ Layered Double Hydroxides / Metal Oxides / Nickel /Chromium