Experimental and density functional theory investigations on the oxidation of typical aromatics over the intermetallic compounds-derived AuMn/meso-Fe2O3 catalysts

Abstract

Aromatic volatile organic compounds (VOCs) are usually pollutants to the atmosphere environment and human health. In the present work, we first adopted the co-reduction and KIT-6-templating strategies to prepare the AuxMny intermetallic compounds and mesoporous iron oxide (meso-Fe2O3), respectively, and then used the impregnation method to generate the AuxMny/meso-Fe2O3 catalysts. Catalytic performance of these materials was evaluated for benzene, toluene or o-xylene (typical aromatics) oxidation. It is found that the Au5Mn2/meso-Fe2O3 catalyst exhibited the best activity: the temperatures at benzene conversions of 50 and 90 % were 237 and 254 °C at a space velocity of 20,000 mL/(g h), with the TOFAu values and specific reaction rates at 210 and 230 °C being 1.08 and 2.29 s−1, and 6.92 and 11.58 mmol/(gAu s), respectively. Such excellent performance of Au5Mn2/meso-Fe2O3 was related to its well dispersed Au5Mn2 nanoparticles, high adsorbed oxygen species concentration, good low-temperature reducibility, high benzene adsorption capacity, and strong benzene adsorption. The benzene chemisorption mechanism and adsorbed oxygen species could greatly influence the oxidation of benzene. According to the first-principles calculations, we find that benzene adsorption on the surface of Au in Au5Mn2/meso-Fe2O3 was in the form of a π bond, in which the Au could obtain electrons from benzene ring in the presence of benzene adsorption, resulting in a stronger adsorption of benzene and thus increasing the catalytic activity for benzene oxidation. The mechanism of benzene oxidation might take place via the route of benzene → phenol → benzoquinone → maleate (acetate) → carbon dioxide and water.