Fe-Doped Mesoporous Alumina: Facile One-Pot Synthesis, Modified Surface-Acidity and Its Enhanced Catalytic Performance in Phenol Hydroxylation

Abstract

Fe-doped mesoporous alumina (MA) was successfully synthesized via a facile one-pot synthesis method. The resulting Fe-doped MA samples possess typical mesoporous structure, relatively high BET surface area, and narrowed pore size diameter. Besides, the iron species are well-dispersed in the alumina matrix, and more importantly, some small oligonuclear iron oxide clusters are linked on the surface of alumina, leading to the elimination of strong acid sites. The reaction of phenol hydroxylation was preceded at room temperature for 2 h. The introduction of mesoporous structure in alumina would be favorable for the adsorption and diffusion process of reactant and product molecules, and also the well-dispersed iron species in alumina matrix and large amount of acid sites stimulate more active hydroxyl radicals which are greatly beneficial for the catalytic process, especially the elimination of strong acid sites would inhibit the over-oxidation reaction. In this case, the sample of 5Fe–MA displays the best catalytic performance especially with the extremely high dihydroxybenzene selectivity of 93.2%, and the good catalytic stability is also evidenced by the five times recycling tests. In this work, the Fe-doped mesoporous alumina (MA) was successfully prepared. The iron species are well-dispersed in the alumina matrix, and some small oligonuclear iron oxide clusters are linked on the surface of alumina, leading to the elimination of strong acid sites. The advanced properties of mesoporous structure, well-dispersed metal active centers and lack of strong acid sites in Fe-doped MA are greatly beneficial for the catalytic process, especially for the dihydroxybenzene selectivity with extremely high value of 93.2%.