Surface versus bulk alkali promotion of cobalt-oxide catalyst in soot oxidation

• Location of alkali is of high importance for promotion of Co3O4 catalytic activity.
• Bulk promotion leads to enhanced catalytic activity in soot combustion.
• Surface doping decreases the catalytic activity in soot combustion.
• Optimal catalyst lowers soot oxidation temperature by 340 °C.

The effect of surface and bulk alkali (Na, K) promotions on the cobalt-oxide catalyst activity in soot oxidation was investigated. While surface promotion does not alter the cobalt spinel structure, the introduction of alkali into the bulk leads to the formation of layered cobaltates (revealed by XRD, Raman spectroscopy and XPS). The catalytic activity was determined using the temperature programmed oxidation of model soot (Printex 80), both in tight and loose contact conditions. The alkali bulk promotion is much more effective than surface promotion in soot oxidation, lowering the soot ignition temperature by 340 °C for the most active catalyst K0.25CoO2.

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