New Insight into the interaction between hydrocarbons and catalytic surfaces has been acquired by Esso Research scientists using advanced techniques for fundamental studies of adsorption on heterogeneous catalysts. The first results were obtained from a detailed infrared study of adsorbed acetylenes.

Acetylene, deuteroacetylene, methyl and dimethyl acetylenes are strongly chemisorbed on alumina even at room temperature. The first three can also exist in a weakly adsorbed state. The strongly held species are held perpendicular to the surface through the acetylenic hydrogens, except dimethyl acetylene, which is held parallel to the surface. All the weakly held acetylenes are held parallel to the surface. The sites responsible for the strong chemisorption of acetylenes are different from those responsible for the strong adsorption of dimethyl acetylene. Surprisingly, no strong chemisorption of either acetylene or dimethyl acetylene was observed with silica.

These results raise several challenging fundamental concepts. Thus, the head-on adsorption is quite unexpected for a molecule containing a reactive triple bond, and it is perhaps surprising that only substitution by two inductive methyl groups can activate the acetylenic triple bond sufficiently for sideways adsorption. Finally, the great difference between SiO2 and Al2O2 raises important questions concerning the role of the oxide in the adsorption.

This work is continuing together with other basic studies of adsorption on catalysts including such advanced methods as microcalorimetry and conductivity.

...adapted from a scientist's notes at Esso Research and Engineering Company P.O. Box 45B, Linden, New Jersey.