Abstract
Recent experiments have shown that silver salts supported on mesoporous silicas display excellent adsorption
selectivities of ethylene over ethane and propylene over propane. Employing the techniques of density functional
theory, we have investigated the fundamental bases of this separation process by examining silver salts dispersed on
model silica surfaces. Our model system includes Ag+ cations, their counteranions, silica supports, and surface
silanols. Both adsorption geometries and energetics of ethylene and propylene were explored. Our results indicate
that the nature of the Ag-olefin interaction is predominantly hybridization between Ag d and olefin � states, which
is supported by analyses of electron density difference plots and density of states. The counteranions, such as NO3
-,
were found to interact strongly with surface silanols through multiple hydrogen bonds but have limited effect on the
adsorption energy of olefins on the Ag+ cations. The current work supports recent experiments, which indicate that
Ag-salt/silica may be a very promising adsorbent for olefin/paraffin separation.
