Gas-phase hydrogenation of acetonitrile was carried out over platinum catalysts using silica (SI), silica-alumina (SA), alumina (AL), and titania (TI) as supports. The Pt/SI, Pt/SA, and Pt/AL catalysts produce triethylamine as the only major product while the Pt/TI catalysts produce triethylamine and diethylamine with a small amount of ethylamine. The Pt/SA and Pt/AL catalysts reduced at low temperature indicate an induction period, giving no products at the beginning of the reaction. All the catalysts lose their activity during the reaction. The initial turnover frequencies (TOF0) are larger for the smaller degrees of platinum dispersion (D). The TOF0-D relation is correlated by the same curve for SI-, SA- and TI-supported catalysts. The TOF0 of Pt/AL catalysts is smaller compared with that of other catalysts. Adsorbed triethylamine was found to decompose at temperatures above 450 K, evolving hydrogen and leaving carbon-containing species, causing the induction period and deactivation. The X-ray photoelectron spectroscopy Pt 4f binding energies of Pt/AL and Pt/TI catalysts were observed to be higher and lower, respectively, compared with that of the Pt/SI catalyst. When acetonitrile is adsorbed on Pt/AL catalyst, it is stabilized and the C-N bond is more difficult to hydrogenate, giving a smaller TOF0 value. The adsorption of basic substances of amines by Pt/TI catalyst is so weak that it produces larger amounts of the lower amines.