AN INFRARED INVESTIGATION OF THE ADSORPTION OF METHANOL AND ETHANOL ON ALUMINUM OXIDE

Author Institution: Research Division, Allis-Chalmers Mfg. Co.The adsorbed surface species which result when $Al_{2}O_{2}$ is exposed to methanol or ethanol vapor have been studied by investigating their infrared spectra. The spectra of three different surface species have been identified for both methanol and ethanol. At $35^{\circ}C$ with a methanol vapor pressure of 40 mm of Hg, a layer of weakly adsorbed molecules gives a spectrum resembling that of liquid methanol. This adsorbed layer disappears upon evacuation at $35^{\circ}C$. Another species persists after prolonged evacuation. It is tentatively identified as a $CH_{3}-O-$ group bonded to a surface aluminum atom, giving a surface compound resembling a methoxide. When the $Al_{2}O_{3}$ is heated to $170^{\circ}C$ in methanol vapor a new surface species is formed. The nature of the absorbed species inferred from the spectrum is as follows: The hydroxyl hydrogen and two of the methyl hydrogen atoms are dissociated from the alcohol molecule which is bonded to a surface oxygen atom through its carbon atom. The resulting configuration is a for-mate-like surface compound. The analogous adsorption process taking place with ethanol, results in an acetate-like surface compound which also has been observed through its infrared spectrum. This interpretation of the surface structure has been checked by using deuterated alcohols and $C^{13}$ enriched methanol, and by observing the band shifts which occur when the surface species is deuterated