Different LDH samples for CO2 capture at various temperatures

https://doi.org/10.1039/C9DT03913A

“The resultant organic–inorganic composite is expected to act as a novel and improved sorbent for high temperature CO₂ capture due to: (a) it having a high surface area compared to similar sorbents and (b) the MMOs being supported on a large sheet of carbon, providing both thermal and mechanical stability. At the same time, the supported carbon sheet can help in the distribution of the active sorbent, CaO. The presence of amorphous aluminium containing phases in the MMOs is known to act as a support for the active sorbents. There is no known evidence of direct aluminium participation in CO₂ capture by MMOs derived from LDHs.³⁴ In the present case, aluminium containing phases are expected to provide additional support to CaO, along with the residual carbon. The resultant composite is expected to facilitate easy accessibility/diffusion for CO₂ to the active phase, CaO, and thereby improves the overall capture performance of the material. In order to identify the optimum temperature for CO₂ capture for the resultant composite, capture studies were carried out from 200 to 700 °C using TGA (86% CO₂, 14% N₂, 100 mL min⁻¹ flow rate). The results are tabulated as shown in Table 1. The sample shows increasing CO₂ adsorption capacity from 200 to 600 °C (from 1.31 mmol g⁻¹ to 6.18 mmol g⁻¹, respectively). The adsorption capacity starts decreasing above 600 °C. The sample shows a CO₂ capture capacity of 5.18 and 4.9 mmol g⁻¹ at 650 and 700 °C, respectively. The CaO-based sorbents are known to show maximum CO₂ adsorption capacity at 600–650 °C due to maximum carbonation/activation at this temperature.³⁵ Interestingly, at 600 °C, most of the calcium present in the nanocomposite (∼27 wt%, 6.13 mmol g⁻¹) has been carbonated due to the MMOs being highly porous, well-dispersed and supported by the sheet-like carbon. The CO₂ uptake values show the near 100% carbonation of all the calcium present in the sample.”