Density functional theory studies on the reaction mechanisms of silver ions with ethylene in facilitated transport membranes: A modeling study

Facilitated olefin transport has been observed through membranes containing AgBF4 dissolved in poly(ethylene oxide) (PEO), but not through ones contai ning AgNO3 according to the previous studies. The difference in facilitated transport behavior between the two systems was theoretically investigated in terms of the mechanism on facilitated transport, in particular, the inte raction of the silver cation with olefin using the density functional theor y (DFT) method. It was found that the reaction of silver cation with ethyle ne occurred through two steps: (i) addition of one ethylene molecule to a s ilver cation dissolved in PEO, (ii) replacement of the ethylene molecule co ordinated on the silver cation with another ethylene molecule. In the two-s tep mechanism of the addition and replacement reactions, the addition react ion is a nonactivated, preequilibrium process and the replacement reaction occurred through a transition state of two ethylene molecules coordinated t o a silver cation dissolved in PEO. It was also found that the PEO/AgBF4 sy stem was energetically more favorable for the facilitated olefin transport than the PEO/AgNO3 system. These results were well accordant with the exper imental results.