An inelastic neutron scattering and NIR-FT Raman spectroscopy study of chloroform and trichloroethylene in faujasites

Molecular information about the nature and the strength of the interactions between chloroform and trichloroethylene (TCE) sorbates and siliceous FAU, NaY, and NaX zeolites was obtained by inelastic neutron scattering (INS) and Raman spectroscopies. The spectral features of the two sorbates differ in terms of their frequencies, splittings, and line widths from the ones of chloroform and TCE molecules in the gas phase. In conjunction with our simulation results, these differences are rationalized by assuming that, in siliceous FAU, the two sorbates undergo a nondissociative adsorption involving the formation of an H(sorbate)... O(framework) hydrogen bond and Cl(sorbate)... O(framework) van der Waals interactions, whereas in NaY and NaX, additional Cl(sorbate)... Na(+) electrostatic interactions are involved. Interestingly, no pi/Na(+) interaction takes place for TCE. These findings, which are in agreement with previous calorimetric and simulation results, confirm that the strength of the sorbate/zeolite interactions is correlated to the basicity of the zeolite and therefore increases in the sequence siliceous FAU < NaY < NaX, following the sequence of the heats of adsorption.