Engineering Highly Efficient Mullite SmMn 2 O 5 Catalysts for Selective Aerobic Solvent‐Free Oxidation of Toluene to Benzoic Acid

ABSTRACT Benzoic acid is produced via the selective oxidation or chlorination‐hydrolysis of toluene, suffering from the high recovery cost of homogeneous catalysts, or the severe corrosion and the chlorine‐contamination of products. Herein, the SmMn 2 O 5 catalyst with a mullite structure was prepared by hydrothermal synthesis followed by an etching treatment. The resulting catalyst was tested for the selective oxidation of toluene to benzoic acid under solvent‐free conditions using molecular oxygen. The etching by nitric acid not only enhanced the textural properties, and surface oxygen vacancy concentration of the mullite SmMn 2 O 5 , but also promoted the reduction of Mn species and the transformation Mn 4+ to Mn 3+ ions. The well‐engineered catalyst exhibited outstanding catalytic performance for the selective aerobic oxidation of toluene to benzoic acid under solvent‐free conditions. A toluene conversion of 31.7% and benzoic acid selectivity of 86.1% was realized under the optimal synthetic and reaction conditions. The reusability of the catalyst was well confirmed after multiple recycling runs on the basis of its structural and textural properties and catalytic performance. The manganese‐based mullite catalyst fabricated via hydrothermal synthesis and etching may offer new insights for the design and industrial application of catalysts for toluene oxidation.