Fabrication of Hierarchical Porous Metal Oxides by the HPMC-Assisted Gel Combustion Strategy: Incorporation of Nanoceria into Cookie-like Mn<sub>2</sub>O<sub>3</sub> with Enhanced Oxidation Activity and Excellent Water Resistance
Yijia Cao, Fujun Li, Chi Zhang, Haotian Wang, Zongpeng Zou, Shengwei Tang, Yunfa Chen, Wenxiang Tang
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.