Infrared Study of the Adsorption of Methanol and Ethanol on Magnesium Oxide

Publisher Website
Google Scholar
Abstract
The adsorbed species which result when magnesia is exposed to methanol or ethanol vapor are reported. Five different surface species have been identified for both methanol and ethanol. At 25°C a tightly bound layer of liquid alcohol is observed. When this is removed by heat and evacuation, another species appears which is identified as a surface methoxide in the case of methanol and ethoxide in the case of ethanol. When the magnesia sample is heated to 165°C in alcohol vapor, a formatelike surface compound is formed from methanol and an acetatelike compound from ethanol. At temperatures near 430°C, two more surface species are observed to form after the disappearance of surface formate (or acetate). They are identified as a surface methyl carbonate from methanol (ethyl carbonate from ethanol) and surface carbonate which is formed from both methanol and ethanol. Both the surface alkyl carbonate and surface carbonate are attributed to a low-temperature (<240°C) reaction between surface alkoxide and CO2 which is liberated by dicarboxylation of the surface carboxylate. The interpretation of surface structures has been checked by using CD3 methanol and 13C enriched methanol. Proposed mechanisms for the formation of the different surface species (followed by mass spectrometry) are discussed.