Catalytic systems for CO2 hydrogenation

7 Carbon Dioxide Conversion in High Temperamre Reactions 

Recently, multi-walled carbon nanotubes (CNT) have drawn increasing attention as catalyst support because of their unique features such as nanometer-sized channels and sp -C bonding, possessing high electron- and thermal-conductivity and large surface area. Zha et al. [229] have deposited Cu0-Zn0-Al203 and 

Silica is commonly used as support because of some desirable properties such as porosity, acidity, and thermal stability [211], To enhance the strength of catalysts, and especially for lower temperature operations, binders are sometimes added. At higher temperatures, these binders are chemically reactive. For example, adding an alumina binder to an Fe-K/Al203 catalyst has been shown to improve the activity and selectivity towards higher hydrocarbons (C5+), whereas when using silica as binder, the activity and selectivity dramatically decreased. This was attributed to the change of catalyst acidity and of the structure and metal-support interaction, which influence the activity and selectivity of the catalyst [253]. 

Cobalt catalysts are widely used for the traditional Fisher-Tropsch synthesis based on CO and H2. Despite being active for CO2 hydrogenation, Co catalysts have been found to promote the formation of tmdesired methane [257]. By replacing the Syngas feed-stream with CO2 and H2, it was foimd that cobalt is prone to be more selective towards methanation rather than methanol or other alcohol production [4, 258,259]. However, it is important to ensure that the catalyst 

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