Tailoring manganese oxide catalysts for the total oxidation of pollutants in gas and liquid phase

Bare and ceria-promoted MnOx catalysts (0 <=chi(Mn)<= 1) were prepared by redox-precipitation reactions of Mn(VII), Mn(II) and Ce(III) or Ce(IV) precursors in slightly acidic (pH, 4.5) or basic (pH, 8.0) environment to assess genesis, nature, and functionality of surface active sites. Both synthesis protocols yield nanostructured materials with large surface area and exposure of Mn sites, featuring high activity in the CO oxidation and the phenol wetair-oxidation (CWAO) model reactions (T, 423 K). High oxide dispersion prompts an extensive incorporation of Mn(II) ions into ceria substitutional solid-solution structures, forming oxygen-vacancies with stronger oxidation activity than surface Mn(IV) sites. Basic structure-activity relationships indicate that the superior CO oxidation performance of the pristine alpha-MnO2 system relies on large exposure of very reducible Mn(IV) active sites, while O-2-adsorption onto Mn(II)/O-vacancy active centres generates very reactive surface oxygen-species boosting the efficiency of composite MnCeOx catalysts in the CWAO of phenol.

Automated summary

The study demonstrates that ceria-promoted MnOx catalysts exhibit high activity in CO oxidation and phenol wet air oxidation reactions. The high oxide dispersion promotes the formation of solid-solution structures between Mn and Ce, enhancing the oxidation activity.