Carbon cycle: capture and activation of carbon dioxide using hydrotalcites

Alsamaq, Suzanne (2012). Carbon cycle: capture and activation of carbon dioxide using hydrotalcites. University of Birmingham. Ph.D.

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Abstract

Dry Reforming of methane (DRM) was performed successfully over hydrotalcite catalysts (A) Ni $^2$ $^+$ /Mg $^2$ $^+$ /Al $^3$ $^+$ , (B) Ni $^2$ $^+$ /Mg $^2$ $^+$ /Al $^3$ $^+$ /Fe $^3$ $^+$ , (C) Ni $^2$ $^+$ /Co $^2$ $^+$ /Al $^3$ $^+$ and (D) Ni $^2$ $^+$ /Co $^2$ $^+$ /Al $^3$ $^+$ /Fe $^3$ $^+$ . The highest conversions for CH $_4$ and CO $_2$ were 85% and 75% respectively, achieved at 750°C, CO $_2$ /CH $_4$ ratio of 1.50 with a residence time of 2.4 seconds over catalyst B. Activation energy was calculated for the DRM reaction of 81.5 kJ mol $^-$ $^1$ . A coke formation study showed that catalyst B formed the lowest weight percentage of coke at around 10 ± 4 (wt%) after 5 hours of reaction.

Adsorption capacity of CO $_2$ into hydrotalcite was tested in TGA and a fixed bed reactor. Adsorbent B displayed the highest adsorption capacity of CO $_2$ compared to the rest of the adsorbents. CO $_2$ capacities of 0.53 mmol g $^-$ $^1$ over calcined powdered adsorbent B and 0.41 mmol g $^-$ $^1$ upon the pellets were recorded using TGA. The capacity dropped to 0.30 mmol g $^-$ $^1$ when subjected to a dilute CO $_2$ in He flow in the fixed bed reactor. Powdered amine (N2)-modified HTlcs showed a CO $_2$ adsorption capacity of 2.38 mmol g $^-$ $^1$ measured using TGA. The best adsorption capacity of CO $_2$ over tablets was with amine (N2)-modified HTlcs in a fixed bed reactor at 2.85 mmol g $^-$ $^1$ .