Hierarchical flower-like Co–Cu mixed metal oxide microspheres as highly efficient catalysts for selective oxidation of ethylbenzene

Abstract

The selective oxidation of alkanes and alkylaromatics to corresponding alcohols, ketones or carboxylic acids is of great importance for the production of high added-value raw materials in the fine chemical industry. The design and synthesis of cost-effective and recyclable heterogeneous oxidation catalysts has become one of the most active research areas. In this work, a series of novel Al2O3@Co–Cu–Al mixed metal oxide (Al2O3@CoCuAl-MMO) catalysts with hierarchical flower-like microstructure were successfully prepared via a Co–Cu–Al layered double hydroxide precursor route, and their catalytic performance was investigated in the liquid-phase selective oxidation of ethylbenzene using tert-butyl hydroperoxide as oxidant without the addition of any organic solvents. The characterization results revealed that the incorporation of copper into the MMO could induce the formation of the interactions between the Co–Cu species, and thus catalytic performance of as-formed Al2O3@CoCuAl-MMO catalysts was significantly promoted. In the selective oxidation of ethylbenzene, a high conversion of 92.8% with an acetophenone selectivity of 89.4% was achieved over the Al2O3@CoCuAl-MMO catalyst with a Cu/(Cu+Co) molar ratio of 0.25. The high catalytic efficiency was attributed mainly to the synergistic effect between highly dispersed active Co and Cu species. More importantly, the obtained catalysts having good recyclability and stability displayed good catalytic performance in the oxidation of other alkanes and alkylaromatics including 1,2,3,4-tetrahydronaphthalene, toluene, cumene, and methylcyclohexane.