Gas phase hydrogenation of acetonitrile and butyronitrile over supported transition metal catalysts was carried out in a gas phase microflow reactor at 1 and 10 bar; butyronitrile was also hydrogenated in a stirred autoclave at an initial pressure of 24 bar Catalyst stability is higher in the Liquid phase than in the gas phase operation, suggesting desorption of site blocking molecules into the liquid. Agglomeration of metal particles has been detected by TEM and EDX; with Pt/NaY it starts at 110 degrees C, with Ru/NaY it is obvious at 160 degrees C. Metal agglomeration and formation of an overlayer contribute to catalyst deactivation. Ru/zeolite catalysts are more active than Ru/Al2O3, both in the gas and the liquid phase. No significant effect of support acidity on the selectivity of the reaction has been detected; the results give no indication of carbide or nitrile formation as major causes of catalyst deactivation.