Thermodynamic data of adsorption reveal the entry of CH and CO in a smectite clay interlayer.

The ability of smectite clays to incorporate gases in their interlayers is shown to be conditioned by interlayer spacing, depending, in turn, on phyllosilicate layer composition and effective size of the charge-balancing cations. As illustrated by earlier in situ X-ray diffraction and spectroscopic characterization of the gas/clay interface, most smectites with small-size charge-balancing cations, such as Na or Ca, accommodate CO and CH in their interlayers only in a partially hydrated state resulting in the opening of the basal spacing, above a certain critical value. In the present study CH and CO adsorption isotherms were measured for Na- and Mg-exchanged montmorillonite up to 9 MPa using a manometric technique.