Modulating the Microstructure and Surface Acidity of MnO₂ by Doping-Induced Phase Transition for Simultaneous Removal...

It is a great challenge to remove VOCs and NO simultaneously from flue gas in nonelectric industries. This study focuses on the construction of Fe-MnO₂ catalysts that perform well in the simultaneous removal of toluene and NO at low temperatures. Utilizing the Fe-induced phase transition of MnO₂, Fe-MnO₂-F&R catalysts with a composite morphology of nanoflowers and nanorods were successfully prepared that provided an abundant microporous structure to facilitate the diffusion of molecules of different sizes. Through in-depth investigation of the active sites and reaction mechanism, we discovered that Fe-induced phase transition could modulate the surface acidity of Fe-MnO₂-F&R. The higher concentration of surface Mn⁴⁺ provided numerous Brønsted acid sites, which effectively promoted the activation of toluene to reactive intermediates, such as benzyl alcohol/benzoate/maleic acid. Simultaneously, Fe provided a large number of Lewis acid sites that anchor and activate NH₃ species, thereby inhibiting NH₃ nonselective oxidation. Furthermore, additional Brønsted acid sites were generated during the simultaneous reaction process, enhancing toluene activation. Consequently, the simultaneous removal of toluene and NO was achieved through regulation of the physical structure and the concentration of acidic sites. The present work provides new insights into the rational design of bifunctional catalysts for the synergistic control of VOCs and NO emissions.