No abstract

We have investigated by in situ neutron diffraction the structural properties of C2HCl3, C2Cl4, and C6D6 sorbed phases in silicalite-1. Our motivation is to correlate the structure of these three confined species to the fact that their adsorption isotherms are characterized by no step, one step, and two steps, respectively. From our detailed neutron diffraction investigation, we deduce that the adsorption isotherm steps are not signatures of phase transitions but are correlated to the different adsorption stages observed during the silicalite-1 loading. For C6D6, such a loading is a three stage process (the C6D6 molecules fill successively, the intersections, then the straight channels and the sinusoidal channels by forming dimers and then interconnecting monomer chains). Concerning C2Cl4, it is a two stage process (the C2Cl4 molecules fill the intersections and after indifferently the straight channels and the sinusoidal channels). Usual sorption is observed for C2HCl3, which fills all parts of the silicalite-1 porosity indifferently. In addition, this comparative study highlights that a step-filling process takes place in the silicalite-1 as far as the symmetry of the sorbed molecule is concerned.