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

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 (Mn2O3-H) was prepared by a hydroxypropyl methylcellulose-assisted combustion synthesis strategy for catalytic complete oxidation of gaseous toluene. Benefiting from the rich porous nanostructure, Mn2O3-H has much higher specific surface area and active site density, resulting in better low-temperature reducibility and oxygen activation ability than blank Mn2O3 formed by direct calcination. With this sol–gel combustion process, CeO2 nanoparticles could be successfully introduced to form cookie-like Ce–Mn composite oxide with a hierarchical porous nanostructure, which builds the strong interaction of CeO2–Mn2O3 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 Mn2O3-H and Mn2O3-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.