Modification of manganese oxide by Ag loading with different synthesis methods for toluene combustion

Abstract

Different Ag/MnO_x catalysts were synthesized by one-pot reflux, ion-exchange and impregnation methods, and their catalytic activity for toluene oxidation and physicochemical properties were investigated in this study. The addition of Ag via one-pot reflux led to the migration of lattice oxygen, an increasing amount of Mn₂O₃ and a higher concentration of oxygen vacancies between the interface of Mn₂O₃ and octahedral molecular sieve-2 (OMS-2). These factors effectively improved the capability of lattice oxygen species to participate in the reaction, thereby facilitating the regeneration of oxygen vacancies, accelerating the consumption rate of intermediate products and enhancing the performance of the catalyst. The impregnation method led to the dispersion of metallic Ag⁰ species on the MnO_x surface, resulting in a catalyst with the best oxygen mobility. However, the catalyst only exhibited the second-best catalytic activity due to a lower amount of active oxygen species. Ag⁺ species were incorporated into the OMS-2 framework by an ion-exchange method, which enhanced the oxygen mobility, but the catalyst showed poor catalytic performance because of the insufficient activation of oxygen species.