Knowledge Bank

The infrared spectrum of acetylene chemisorbed on silica-supported nickel (9.2 wt. %) has been obtained. As in chemisorbed ethylene the absorption due to C-H stretching was essentially in the region characteristic of saturated hydrocarbons. But unlike chemisorbed ethylene, the chemisorbed acetylene spectrum shows evidence of the existence of $-CH3$ groups by a sharp absorption band at 7.25 microns. Attempts were made to rule out effects due to residual surface hydrogen by chemisorbing acetylene on a de-hydrogenated surface and also on a deuterated surface. However in both cases the presence of $CH2$ and $CH3$ groups was indicated in the spectra of the chemisorbed acetylene. It was therefore concluded that self-hydrogenation takes place with some acetylene molecules giving up hydrogen atoms to others to form chemisorbed ethyl groups, $C\ast H2CH3$, and a surface carbide.