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 Al 2 O 3 surface with a bifunctional adsorbate, 2-chloroethylethyl sulfide, was studied by transmission infrared spectroscopy. Al 2 O 3 has five unique Al−OH groups, differentiated by their coordination to the surface, which give independent AlO−H stretching modes. Monitoring intensity changes in these modes as 2-chloroethylethyl sulfide (CEES) molecules diffuse into the porous structure of alumina shows distinctly different stages of surface diffusion and reaction at the Al−OH groups. Three sequential steps have been separated by studies at low temperature, where the rate of the processes was kinetically retarded to allow observation. The final stage of the CEES interaction with the surface occur when the CEES molecules adsorbed on the surface via the sulfide moiety at Al 3+ Lewis acid sites undergo a hydrolysis reaction with the neighboring basic Al−OH groups.