Boosting catalytic oxidation of toluene on MnCo/AC by synergistic effect of Mn-Co oxides and AC support

Activated coke (AC), with well-developed porous structure, has been extensively applied as adsorbents and support of catalysts for air pollutants control. In this work, Mn-Co oxides supported on AC were synthesized for toluene removal. The optimal Mn₁Co₉/AC exhibited remarkable toluene removal efficiency above 90 % at 238 ℃, comparable to some pure metal-oxides catalysts but with a lower cost. Besides, Mn₁Co₉/AC sustained toluene removal efficiency above 80 % even with 500 ppm SO₂ or 10 vol% H₂O at 240 ℃, implying its potential of industrial application. Characterizations revealed that the strong metal oxides-support interaction endowed Mn₁Co₉/AC with enhanced adsorption of reactants, highly-dispersed active components and accelerated electron transport. Additionally, the synergy between MnO_x and CoO_x facilitated the formation of active oxygen species, including abundant surface adsorbed oxygen, oxygen vacancies and lattice oxygen with high mobility, metal ions with higher valence, and thus superior reducibility. Combined with FTIR, the initial oxidation of toluene → benzyl alcohol → benzaldehyde → benzoic acid proceeded at lower temperature, while the further oxidation of benzoic acid → maleic anhydride → carbonates → CO₂ + H₂O occurred with elevated temperature. And O₂ facilitated both toluene adsorption and subsequent oxidation of intermediates, especially for benzyl alcohol oxidation, via continuous replenishment of consumed active oxygen species.