  We investigate the mechanical and adsorption properties of single-walled
carbon nanotubes (SWCNTs) filled with greenhouse gases through Grand Canonical
Monte Carlo (GCMC) and Molecular Dynamics (MD) simulations using a recently
developed parameterization for the cross-terms of the Lenard-Jones (LJ)
potential. Carbon nanotubes interact strongly with CO$_2$ compared to CH$_4$,
resulting in a CO$_2$-rich composition inside the nanotubes, with the
proportion of CO$_2$ decreasing as the diameter of the nanotubes increases.
Contrarily, the smallest nanotubes showed a more even balance between CO$_2$
and CH$_4$ due to gas solidification. The gas does not affect the mechanical
response of the nanotubes under tension, but under compression, it presents a
complex relationship with the loading direction, nanotube's diameters,
chirality, and to a minor extent, the gas composition. Filled zigzag nanotubes
showed to be more stable in the presence of fillers, giving the best mechanical
performance compared to the filled armchairs. The study confirms carbon
nanotubes as effective means of separating CO$_2$ from CH$_4$, presenting good
mechanical stability.
