Bimetallic Mn-Cu oxide catalysts for toluene oxidation: Synergistic effect and catalytic mechanism

Abstract

A series of Mn-Cu composite oxides with different Mn/Cu molar ratios were synthesized via a facile ethanol-redox precipitation method and investigated for the oxidation of toluene. Among as-synthesized MnxCuy catalysts, Mn5Cu1 showed the most excellent toluene catalytic activity at a weight hourly space velocity (WHSV) of 30000 mL∙g−1∙h−1, with 90 % conversion achieved at 212 °C. Furthermore, the Mn5Cu1 catalyst exhibited exceptional thermal stability over a 12-hour period at 215 °C, along with outstanding resistance to H2O in the range of 5 vol% to 40 vol%. As characterized by XRD, BET, XPS, EPR, H2-TPR, and O2-TPD, it was found that Mn5Cu1 possessed a unique three-phase coexisting structure, large specific surface area (57 m2·g−1), plentiful oxygen vacancies, excellent redox capacity, and strong mobility of oxygen, which were attributable to the synergistic effect between Mn and Cu. This strong synergy between Mn and Cu is the underlying reason for the strong catalytic activity of Mn5Cu1. Moreover, toluene-TPD and TPSR results indicated that appropriate Cu loading was favorable for the adsorption and activation of toluene. The potential reaction pathway for toluene oxidation was presented based on in situ DRIFTS characterization. Maleic anhydride was the critical reaction intermediate species.