Infrared spectroscopic study of surface diffusion to surface hydroxyl groups on Al2O3: 2-chloroethylethyl sulfide adsorption site selection

The interaction of the various hydroxyl groups on the Al2O3 surface with a bifunctional adsorbate, 2-chloroethylethyl sulfide, was studied by transmis sion infrared spectroscopy. Al2O3 has five unique Al-OH groups, differentia ted by their coordination to the surface, which give independent AlO-H stre tching modes. Monitoring intensity changes in these modes as 2-chloroethyle thyl sulfide (CEES)molecules diffuse into the porous structure of alumina s hows distinctly different stages of surface diffusion and reaction at the A l-OH groups. Three sequential steps have been separated by studies at low t emperature, where the rate of the processes was kinetically retarded to all ow observation. The final stage of the GEES interaction with the surface oc cur when the GEES molecules adsorbed on the surface via the sulfide moiety at Al3+ Lewis acid sites undergo a hydrolysis reaction with the neighboring basic AI-OH groups.