An upward shift of 0.8 +/- 0.1 eV is measured on the Pd 3d core levels of Pd atoms deposited on Ni(110) with respect to pure Pd surface atoms. These electronic properties are found to be unchanged in the course of a 475 K thermal treatment whereas the activity of the annealed deposit towards the butadiene hydrogenation reaction is largely enhanced. Consequently, electronic effects are not sufficient to explain the activity enhancement. The LEIS technique reveals that the Pd atoms remain at the very surface of the sample, the Pd concentration being roughly 48 at%. Therefore, some geometric effects have to be taken into consideration. The annealing would lead to a particular arrangement and would generate more effective catalytic sites.