Insights into the active sites of ordered mesoporous cobalt oxide catalysts for the total oxidation of o-xylene

- Ordered mesoporous Co3O4 (meso-Co3O4) is prepared via the KIT-6-templating route.
- meso-CoO and meso-CoOx are fabricated from meso-Co3O4 via a reduction process.
- meso-CoOx with the largest surface Co2+ amount performs best for o-xylene oxidation.
- Surface Co2+ species are beneficial for oxygen activation.
- Active oxygen species formed in the Co2+ sites are mainly O2− and/or O22−.

Cobalt oxide is a typical transition metal oxide that exhibits high catalytic activity for the total oxidation of volatile organic compounds. In this study, a reduction process in a glycerol solution was adopted to generate mesoporous CoO (meso-CoO) or CoOx (meso-CoOx) from mesoporous Co3O4 (meso-Co3O4). The obtained samples were rich in Co2+ species and exhibited high catalytic activity for o-xylene oxidation. The meso-CoOx sample with the largest surface Co2+ amount performed the best: The o-xylene conversion at 240 °C was 83%, and the reaction rate over meso-CoOx was nine times higher than that over meso-Co3O4. It is found that the samples with more surface Co2+ species possessed better oxygen activation ability, and the Co2+ species were the active sites that favored the formation of highly active O2− and O22− (especially O2−) species.

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