Fabrication of Hierarchical Porous Metal Oxides by the HPMC-Assisted Gel Combustion Strategy: Incorporation of Nanoceria into Cookie-like Mn₂O₃ with Enhanced Oxidation Activity and Excellent Water Resistance

Abstract

Constructing nonprecious metal oxide catalysts with a hierarchical porous structure by a simple method for the deep catalytic oxidation of toxic volatile organic compounds at low temperatures is of great value and significance. In this work, a porous manganese trioxide catalyst (Mn 2 O 3 -H) was prepared by a hydroxypropyl methylcellulose-assisted combustion synthesis strategy for catalytic complete oxidation of gaseous toluene. Benefiting from the rich porous nanostructure, Mn 2 O 3 -H has much higher specific surface area and active site density, resulting in better low-temperature reducibility and oxygen activation ability than blank Mn 2 O 3 formed by direct calcination. With this sol−gel combustion process, CeO 2 nanoparticles could be successfully introduced to form cookie-like Ce−Mn composite oxide with a hierarchical porous nanostructure, which builds the strong interaction of CeO 2 − Mn 2 O 3 to weaken Mn−O with more active defects. Among Ce-doped catalysts, 5% CeMn-H shows the best catalytic activity in toluene oxidation with 90% conversion temperature at 242 °C under a weight hour space velocity of 60,000 mL•g −1 •h −1 , which is about 30 and 133 °C lower than that of Mn 2 O 3 -H and Mn 2 O 3 -B, respectively. This advantage is also shown in other typical hydrocarbons such as propylene and propane. Moreover, the as-prepared Ce-doped catalyst exhibits excellent stability and water resistance ability. This simple robust sol−gel combustion method will provide valuable enlightenment for designing porous catalysts with high performance for related catalytic reactions.