Atomic layer deposition (ALD) in preparation of MWCNT-supported Pd catalysts was compared to dry and wet impregnation. The prepared catalysts were characterized by various methods and cinnamaldehyde hydrogenation was used as a model reaction to test the activity of the prepared catalysts. The main factor affecting the properties of the catalyst was found to be the precursor medium used during catalyst preparation. ALD, with a gaseous precursor, led to the smallest metal particles with the highest dispersion, whereas impregnation methods using liquid precursors led to the largest particles with the lowest dispersion. The variation in the metal particle sizes of different catalysts was shown to affect the product distribution in the model reaction and the reaction mechanisms of the surface reactions.