Solvent-free oxidation of ethylbenzene over hierarchical flower-like core-shell structured Co-based mixed metal oxides with significantly enhanced catalytic performance

Herein, we reported the development of new and cost-effective cobalt-based metal oxide catalysts for the oxidation of ethylbenzene, which is considered to be of much importance for the production of high value-added raw materials. The heterogeneous Co-based catalyst system, hierarchical flower-like core-shell structured Co-Zn-Al mixed metal oxides supported on alumina (CoZnAl-MMO/Al2O3), was reproducibly prepared by a two-step process, which involved in situ growth of a two-dimensional Co-Zn-Al layered double hydroxide precursor on amorphous alumina microspheres followed by calcination. The materials were characterized by XRD, SEM, TEM, HRTEM, TPR, XPS and nitrogen adsorption-desorption measurement. The results revealed that CoZnAl-MMO/Al2O3 catalysts exhibited high dispersion of cobalt species due to well-developed three-dimensional flower-like CoZnAl-MMO platelets as well as the separating effect of the resulting ZnO phase. As-synthesized CoZnAl-MMO/Al2O3 catalysts were studied in the oxidation of ethylbenzene without the addition of any solvent and additive using tert-butyl hydroperoxide as the oxygen source and showed much higher catalytic activity and selectivity for acetophenone compared with the conventional supported Co-based catalyst prepared by incipient impregnation. Furthermore, such cost-effective CoZnAl-MMO/Al2O3 catalysts possessed high stability and could be reused at least three times without remarkable loss of the catalytic activity.