Pd deposits on Ni(110) have been studied by low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), low-energy ion scattering spectroscopy (LEIS), and X-ray photoelectron spectroscopy techniques and their catalytic properties tested by the butadiene hydrogenation reaction at room temperature. Their catalytic activity is greatly enhanced by appropriate annealings, Superstructure indicative of a long range ordering of Pd atoms on Ni is evidenced for low Pd coverages neither before nor after annealing, For higher coverages, a LEED superstructure appears after annealing, AES and LEIS studies reveal a sharp Pd depth profile and the existence of a Pd-Ni surface alloy even at room temperature. The Pd 3d core level binding energy is shifted upwards by at least 0.4 eV with respect to pure Pd surface atoms and remains unchanged in the course of annealings, Hence geometrical rearrangements have to be taken into consideration to explain the activity enhancement.