Strained Pd overlayers on Ni nanoparticles supported on alumina and catalytic activity for buta-1,3-diene selective hydrogenation

To study the role of strain effects on catalytic properties in the case of supported particles, core–shell PdNi bimetallic nanoparticles were prepared by chemical synthesis and studied in hydrogenation of buta-1,3-diene. Multitechnique characterisation (EDS, TEM, EXAFS) results indicate good homogeneity of the bimetallic particles in terms of size and composition. The core–shell structure of NiPd bimetallic particles and the compressive stress induced on Pd atoms in the top layer due to its larger atomic radius compared with Ni, have been evidenced by EXAFS analyses. According to the literature, Pd activity for buta-1,3-diene hydrogenation is amplified when Pd is strained at the surface of Ni single crystal faces, mainly in the case of (110) planes. This compressive stress is supposed to produce surface reconstructions with undulated Pd row structures. In our case, no amplification of the Pd activity for buta-1,3-diene hydrogenation performed in liquid-phase conditions was observed for a monolayer of Pd strained on 5 nm Ni particles. Consequently, the compressive strain on the Pd atoms at the surface of the nanoparticles seems not to play a major role in the amplification of the activity for buta-1,3-diene hydrogenation. Surface reconstructions observed on extended surfaces to relax the surface stress seems to be the key point for Pd activity amplification. For supported particles, we propose that this relaxation phenomenon does not occur for such small three-dimensional particles.