Viability of clathrate hydrates as CO₂ capturing agents: a theoretical study

Abstract

Capture and sequestration of green house gas CO₂ is a major challenge for scientists and identifying right materials for this purpose is a task of outstanding importance. Through reliable computational studies, we have demonstrated that the clathrate cages (5¹², 4³5⁶6³, 5¹²6², 5¹²6⁴, and 5¹²6⁸) have a great potential to store CO₂. All the considered clathrates and their CO₂ inclusion complexes are optimized at B3LYP/6-31G(d) level of theory. The impact of DFT-D, M05-2X, and MP2 functionals on interaction energy were tested using various basis sets. Although different functionals and basis sets show variation in absolute IE values, the trend is consistent and does not depend on the level of the calculations. Dispersion was found important for these complexes and DFT-D shows comparable IE values with MP2 functional. The optimum and maximum cage occupancy for all the considered cages were tested on the basis of quantum chemical calculations. The maximum cage occupancy for all five considered cages (5¹², 4³5⁶6³, 5¹²6², 5¹²6⁴, and 5¹²6⁸) is one, two, two, two, and seven CO₂ molecules, respectively, and the optimum cage occupancy is one, one, one, two, and five CO₂ molecules, respectively. Thus, 5¹²6⁸ cages can host up to 7 CO₂ molecules, resulting in about 32 wt %, which makes them highly promising materials.