Advances on the Carbon Dioxide (CO2) Reactivity on Lithium and Sodium Ceramics and Its Catalytic Conversion to Added Value Products

The anthropogenic amounts of carbon dioxide (CO₂) in the atmosphere have been raised dramatically, mainly due to the combustion of different carbonaceous materials used in energy production, transport and other important industries such as cement production, iron and steelmaking. To solve or mitigate, at least, this environmental problem, several alternatives have been proposed. A promising alternative for reducing the CO₂ emissions is to capture and concentrate the gas and its subsequent chemical transformation.

Different materials have been proposed as potential CO₂ captors. Among these materials, different lithium and sodium ceramics have been proposed as possible high temperature CO₂ captors. Some of the alkaline ceramics most studied are the lithium and sodium silicates (Li₄SiO₄, Li₈SiO₆, Li₂SiO₃ and Na₂SiO₃), lithium aluminate (Li₅AlO₄) lithium and sodium zirconates (Li₂ZrO₃ and Na₂ZrO₃) and lithium cuprate (Li₂CuO₂), among others. All these ceramics have been tested, producing interesting results at different temperature ranges between 30 and 700 °C.

In this kind of ceramics CO₂ capture is produced throughout a chemisorption process. Initially, the alkaline ceramic particles react with CO₂ at the surface. The superficial reaction implies the formation of an external shell of Li₂CO₃ or Na₂CO₃ and secondary phases. Once the external shell is produced, the reaction mechanism is controlled by different diffusion processes. Therefore, the correct understanding of all these phenomena is a very important step during the selection of the ideal CO₂ capture conditions. In other words, the selection of materials, temperature range, gas and/or vapor concentrations, flows, etc. Then, the aim of this work is to present different experiments related to the CO₂ reactivity, chemisorption, on lithium and sodium ceramics and to propose how different factors control this process. The work will be focused on diffusion controlled CO₂ chemisorption, which has been shown to be the limiting step of the CO₂ chemisorption process. Diffusion controlled CO₂ chemisorption appears to be mainly influenced by the chemical composition of a product’s external shell.

Conversely, different catalytic reactions, where carbon dioxide (CO₂) and/or methane (CH₄) are used, have attracted the research attention because of environmental applications. Some of these reactions are the methane reforming (called dry reforming), the water splitting and the CO₂ reduction. All these reactions produce syngas (CO + H₂). The syngas produced by these reactions can be used in different energetic and organic applications. Additionally, these reactions are also environmentally important, as CO₂ and CH₄ (perhaps the two most important greenhouse gases) are catalytically converted into added value products, such as hydrocarbons and oxygenated compounds.

Therefore, the aim of this presentation is to show some new advances in the CO₂ capture on alkaline ceramics and to show as well how the CO₂ chemically trapped can be catalyzed to added value products through the syngas production at different temperature ranges.

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