Sol-gel prepared Co-Mg-O oxide systems: redox behavior, thermal stability and catalytic performance in CO oxidation

In this work, Co-Mg-O oxide systems were prepared via a sol-gel technique. The cobalt loading in the samples was varied from 1 to 45 wt% (in relation to Co3O4). During the synthesis, magnesium methoxide was hydrolyzed by an aqueous solution of cobalt nitrate of corresponding concentration. The desired pH value of the solution was set by the addition of ammonia or nitric acid. The decomposition of xerogel was examined using thermogravimetric method. The prepared Co-Mg-O oxide samples were characterized by low-temperature nitrogen adsorption, X-ray diffraction analysis, and diffuse reflectance UV-vis spectroscopy. Finally, the samples were tested in consecutive redox cycles (temperature-programmed reduction in hydrogen followed by reoxidation in air) and in a model reaction of carbon monoxide oxidation studied under prompt thermal aging conditions. As found, in the case of as-prepared samples, cobalt interacts with MgO with the formation of such a solid solution as MgCo2O4. With an increase in the Co3O4 loading, this interaction becomes stronger. Each reduction/oxidation cycle leads to an emergence of a part of cobalt from the solid solution, thus increasing the amount of isolated Co3O4 particles distributed within the MgO matrix. The sample prepared with the ammonia addition exhibited the highest stability in catalytic runs if compared with other samples. An increase in Co3O4 loading from 5 to 30% decreases the light-off temperature in first runs but affects negatively the thermal stability.

Automated summary

In this work, Co-Mg-O oxide systems were prepared via a sol-gel technique and characterized at different cobalt loading levels. The interaction between cobalt and MgO resulted in the formation of a solid solution, and this interaction became stronger as the cobalt loading increased. Each reduction/oxidation cycle caused a portion of cobalt to emerge from the solid solution. The sample prepared with ammonia exhibited the highest stability in catalytic runs.