Diesel soot elimination over potassium-promoted Co3O4 nanowires monolithic catalysts under gravitation contact mode

- The potassium species improve the stability of the catalyst for soot combustion.
- Interaction between potassium and cobalt species stabilizes part of potassium species.
- The chemisorbed NOx species play a role in the NOx-aided soot combustion process.
- The presence of O2 can accelerate soot combustion with the chemisorbed NOx species.
- The trapped nitrate/nitrite is catalytically inert for soot combustion in the presence of O2.

Herein, we report the high catalytic activity of the potassium-promoted Co3O4 nanowires supported on the monolithic three-dimensional macroporous (3-DM) nickel foam substrate (xKCo-NW) for soot combustion. The 3-DM structure of Ni foam and the space among these nanowires can extremely improve the contact efficiency between soot and catalysts. Loading of potassium provides the new active sites for soot oxidation, improves catalyst-soot contact as a molten salt and increases the number of the surface adsorbed oxygen species. The 5KCo-NW catalyst loaded with 5% potassium shows the highest catalytic performance, as well as a high water resistance. There are two types of potassium species in the catalysts, most potassium species is in the form of separate phases, and few interacts with cobalt oxide. The interaction between potassium species and cobalt oxide stabilizes a part of potassium species, and the stabilized potassium species can promote the catalytic activity for the consecutive soot combustion cycle. Moreover, our results show that the chemisorbed NOx species on the 5KCo-NW catalyst are more active than the gaseous NO2 for soot oxidation. In the presence of O2, soot combustion is accelerated to react with the chemisorbed NOx species; whereas the formed nitrate/nitrite species are catalytically inert.

The potassium-promoted Co3O4 nanowires supported on the monolithic three-dimensional macroporous nickel foam substrate show high catalytic activities for soot combustion under gravitational contact mode, especially with the aid of NOx.125