Lee and coworkers, 2011, proposed the "pressure-and heat-induced insertion of CO2 into an auxetic small-pore zeolite". "When the small-pore zeolite natrolite is compressed at ca. 1.5 GPa and heated to ca. 110 °C in the presence of CO2, the unit cell volume of natrolite expands by 6.8% and ca. 12 wt % of CO2 is contained in the expanded elliptical channels. This CO2 insertion into natrolite is found to be reversible upon pressure release" .