Establishing efficient toluene elimination over cobalt-manganese bimetallic oxides via constructing strong Co–Mn interaction.

Doping proves to be an efficacious method of establishing intermetallic interactions for enhancing toluene oxidation performance of bimetallic oxides. However, conventional bimetallic oxide catalysts are yet to overcome their inadequacy in establishing intermetallic interactions. In this work, the dispersion of Mn–Co bimetallic sites was improved by hydrolytic co-precipitation, strengthening the intermetallic interactions which improved the structural and physicochemical properties of the catalysts, thus significantly enhancing its catalytic behavior. MnCo–H catalysts fabricated by the hydrolytic co-precipitation method showed promising catalytic performance (T 50 = 223 °C, T 90 = 229 °C), robust stability (at least 100 h) and impressive water resistance (under 10 vol.% of water) for toluene elimination. Hydrolytic co-precipitation has been found to improve dispersion of MnCo elements and to enhance interaction between Co and Mn ions (Mn4+ + Co2+ = Mn3+ + Co3+), resulting in a lower reduction temperature (215 °C) and a weaker Mn–O bond strength, creating more lattice defects and oxygen vacancies, which are responsible for superior catalytic properties of MnCo–H samples. Furthermore, in situ DRIFTs showed that gaseous toluene molecules adsorbed on the surface of MnCo–H were continuously oxidized to benzyl alcohol → benzaldehyde → benzoate, followed by a ring-opening reaction with surface-activated oxygen to convert to maleic anhydride as the final intermediate, which further generates water and carbon dioxide. It was also revealed that the ring-opening reaction for the conversion of benzoic acid to maleic anhydride is the rate-controlling step. This study reveals that optimizing active sites and improving reactive oxygen species by altering the dispersion of bimetals to enhance bimetallic interactions is an effective strategy for the improvement of catalytic behavior, while the hydrolytic co-precipitation method fits well with this corollary. Doping is a successful approach to establish intermetallic interactions to improve the toluene oxidation capacity of bimetallic oxides. In spite of this, the classical bimetallic oxide catalysts are still struggling to overcome their inability to establish these interactions. In this work, hydrolytic co-precipitation has demonstrated the ability to enhance MnCo element dispersion and interaction between Co and Mn ions (Mn4+ + Co2+ = Mn3+ + Co3+). As a result, low-temperature reducibility improved while the Mn–O bond strength weakened, leading to more lattice defects and oxygen vacancies, ultimately resulting in superior catalytic properties of MnCo–H samples. [Display omitted] • Revealing the effect of Co–Mn intermetallic interactions on catalytic performance. • Stronger Co–Mn interactions are established by hydrolytic co-precipitation method. • MnCo–H with strong Co–Mn interaction shows favorable stability and H 2 O resistance. • Co–Mn interactions found to act on electron transfer and activation of oxygen. • The in-situ DRIFTS revealed mechanism and rate-limiting steps of toluene oxidation. [ABSTRACT FROM AUTHOR]