Palladium catalysts supported on alpha-Si3N4 were prepared by impregnation with Pd(II)-acetate dissolved either in toluene or in water. The mean metal particle size of similar to 0.5 wt% Pd catalysts was similar (similar to 5 nm) and independent of the way of preparation. Nevertheless, the two catalysts present very different chemisorption behaviour chemisorptive and catalytic properties. Fourier transformed infrared (FTIR) spectra of adsorbed CO at different temperatures (ranging from room temperature to 300 A degrees C) show a very different behaviour for both catalysts. While the CO adsorption states on the Pd/alpha-Si3N4 prepared in toluene are very similar to those generally measured for silica and/or alumina supported palladium catalysts, CO chemisorbs less strongly on Pd/alpha-Si3N4 prepared in water and on different adsorption sites. The Pd/alpha-Si3N4 catalyst obtained by aqueous impregnation is much less efficient for the methane total oxidation. It is less active and less stable: it deactivates strongly after 3 h on stream at 650 A degrees C. The two catalysts present about the same activity for the 1,3-butadiene hydrogenation after stabilisation at 20 A degrees C. But, the catalyst prepared in water shows a much better selectivity to butenes. The results are discussed in terms of the possible migration of silicon atoms from the silicon nitride support to the surface of the palladium particles, when the catalyst is prepared in water. This is not the case when prepared in an organic solvent.