Infrared Study of the Surface Species Formed by Sequential Chemical Vapor Deposition of Trimethylaluminum and Methanol on a Hydroxylated Alumina Surface

Infrared spectroscopy is used to follow the chemical changes, as a function of temperature, after sequentially adsorbing trimethylaluminum (TMA) and methanol on hydroxylated alumina. Deuterium-labeled methanol is used to distinguish between the chemistry of methyl and methoxy species. To differentiate between methanol adsorbed on TMA-derived sites and on alumina, the adsorption of methanol is studied on alumina alone. The coverage of methanol on alumina alone is only 34 ( 2% of that which adsorbs on a TMA-covered surface. Initial adsorption of methanol on Al(CH3)2(ads) formed by TMA adsorption, rapidly replaces a methyl by a methoxy species. Further reaction of methanol at ∼400 K replaces the second methyl species leading to Al(CH3O)2(ads). This thermally decomposes on heating to yield primarily dimethyl ether and surface formate species. It is also very reactive with water and rapidly forms adsorbed hydroxylated alumina and methanol.