Highly active and stable plate-like ZSM‑5 supported MnOx catalysts for toluene Oxidation: Effect of preparation methods

Abstract

Catalysts consisting of MnOx supported on plate-like ZSM-5 with the Si/Al ratio of 70 (MnOx/PZ5) were synthesized using four different methods: in-situ growth (MnOx/PZ5-IG), ammonia precipitation (MnOx/PZ5-AP), citric acid complexation (MnOx/PZ5-CA), and traditional impregnation (MnOx/PZ5-TI). The catalytic activity of these catalysts for toluene oxidation was evaluated, and their physicochemical properties were characterized by several technologies. The results showed the catalytic activity for toluene oxidation was significantly influenced by the preparation methods. Notably, MnOx/PZ5-IG demonstrated the highest catalytic activity for oxidation of toluene with the specific activity per unit mass of Mn with 2.12 × 10-6 at 250 °C, 3.8 times higher than that of MnOx/PZ5-CA, offering new ideas for the design of low-cost materials for VOCs elimination in the future. The excellent performance of MnOx/PZ5-IG could be attributed to the higher Mn4+ ratio with more reducible, active surface adsorbed oxygen and dispersion of MnOx, which also showed high stability. Finally, the reaction mechanism analyzed by in-situ DRIFTS found that MnOx/PZ5-IG promoted the activity of surface lattice oxygen, conducive to increasing the reaction rate and facilitating the ring opening of benzene, thus, deepening the oxidation of toluene to CO2 and H2O.