Effects of supports in gas-phase hydrogenation of acetonitrile over supported platinum catalysts

Gas-phase hydrogenation of acetonitrile was carried out over platinum catal ysts using silica (SI), silica-alumina (SA), alumina (AL), and titania (TI) as supports. The Pt/SI, Pt/SA, and Pt/AL catalysts produce triethylamine a s the only major product while the Pt/TI catalysts produce triethylamine an d diethylamine with a small amount of ethylamine. The Pt/SA and Pt/AL catal ysts reduced at low temperature indicate an induction period, giving no pro ducts at the beginning of the reaction. All the catalysts lose their activi ty 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 T OF0 of Pt/AL catalysts is smaller compared with that of other catalysts. Ad sorbed triethylamine was found to decompose at temperatures above 450 K, ev olving hydrogen and leaving carbon-containing species, causing the inductio n period and deactivation. The X-ray photoelectron spectroscopy Pt 4f bindi ng energies of Pt/AL and Pt/TI catalysts were observed to be higher and low er, respectively, compared with that of the Pt/SI catalyst. When acetonitri le 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 b asic substances of amines by Pt/TI catalyst is so weak that it produces lar ger amounts of the lower amines. (C) 1999 Elsevier Science B.V. All rights reserved.