The rate of hydrogenation of butanal, 2-methylpropanal and 2-ethylhex-2-enal was studied on a copper catalyst in the shape of tablets and Raschig rings at 100 to l60 °C and 7 MPa was studied. It was found that the reaction is strongly affected by internal diffusion since the catalyst particles with a larger external surface (Raschig rings) were markedly more active. A first-order rate law with respect to the hydrogenated aldehydes has been confirmed.