Abstract Colloidal nanoparticle catalysts play a decisive role both in the implementation of a number of important industrial processes, including the hydrogenation of nitro compounds, and in fundamental studies of catalytic reactions on nanoparticles. The laser ablation in liquid (LAL) is a promising method to prepare nanoparticle colloids, and the use of mixed solutions as a medium can be attractive for both preparation of stable colloids and their application in catalysis. While using the LA in water-ethanol solutions, the stable colloids of CuOx NPs demonstrating high catalytic activity in the 4-nitrophenol (4-NP) hydrogenation were prepared. The reasons for the instability of colloids obtained in water and alcohol as well as the stabilization of colloids in water-ethanol solutions were considered. The results obtained contribute to the understanding of the lower catalytic activity of the studied CuOx catalyst in ethanol and other non-aqueous solvents. The presence of ethanol in the reaction medium was found to have an inhibitory effect on the 4-NP reduction kinetics due to the alcohol adsorption on the catalyst surface that is well described within the framework of the Langmuir-Hinshelwood model.