Constructing oxygen vacancies in Cu-doped MnO2 by a quenching strategy for boosting the catalytic oxidation of toluene

Abstract

Here, a quenching strategy was developed to create oxygen vacancies in Cu doped α-MnO₂. The evolutions of oxygen vacancies were directly followed by means of XRD refinement, EPR and XPS. In combination with DFT calculations and detailed characterizations, evidence is captured that oxygen vacancies not only act as direct sites for the adsorption and activation of gaseous oxygen and toluene, but also accelerate the consumption and replenishment cycle of lattice oxygen species by weakening the strength of metal-oxygen bonds. In situ DRIFTS study reveals that both adsorbed oxygen and lattice oxygen species directly participate in the oxidative decomposition of toluene, where adsorbed oxygen species play pivotal roles in the initial oxidation of toluene to benzoate, whereas the process of ring opening of benzoate relies on the activation of lattice oxygen. Benefiting from crucial contribution of oxygen vacancies in activating oxygen species, α-CuMnO₂-500-Q obtained by the quenching method is capable of fully catalyzing the oxidation of toluene at 240 ℃, representing a reduction of about 80 ℃ compared to pristine α-CuMnO₂-500. Furthermore, the toluene oxidation mechanism was proposed as well via in situ DRIFT spectra.