Facile preparation of MnOx catalysts derived from MOFs for efficient toluene Oxidation: Synergistic enhancement of active site density and reactivity

Abstract

Adsorption and activation are essential in heterogeneous reactions, particularly for toluene catalytic oxidation. Synergistically enhancing both processes to boost toluene oxidation activity remains a significant challenge. A facile MOFs sacrificial combined with an alkaline solution post-treatment modification strategy was implemented to prepare hierarchically structured MnO_x nanosheets (MnO_x-S) catalysts. Compared with the Mn₂O₃-H and MnO₂-P catalysts, obtained by the direct pyrolysis of Mn-MOFs and Mn(NO₃)₂ precursors, the MnO_x-S catalyst exhibits a noticeable improvement in catalytic activity for toluene oxidation. The T₉₀ was reduced 26 °C and 64 °C, respectively. The reason is closely related to the porous nanosheet structure, possessing a highly accessible surface and high density of exposed active sites, thus facilitating the adsorption/activation of reactant molecules. Meanwhile, the strong redox ability in the MnO_x-S catalyst boosted oxygen mobility and reactivity, resulting in a 12.4-fold catalytic reaction rate compared with MnO₂-P. The accumulation and conversion of benzoates is the rate-limiting step in the toluene oxidation reaction occurring on three distinct catalyst surfaces. This critical step is notably expedited by especially hierarchical structures in MnO_x-S catalysts. This work advances the investigation of MOF-related catalytic materials and provides a dual approach that simultaneously enhances both adsorption and reaction processes, facilitating the design of high-performance catalysts for VOCs degradation.