Structure sensitivity of selective acetylene hydrogenation over the catalysts with shape-controlled palladium nanoparticles
The structure sensitivity of acetylene hydrogenation on catalysts with controlled shape of palladium nanoparticles was studied. Palladium particles of cubic (Pd-cub), cuboctahedral (Pd-co) and octahedral (Pd-oct) shapes were obtained by a colloidal method. Poly(N-vinyl)pyrrolidone (PVP) was used as the stabilizer of colloidal solutions. In order to eliminate the effect of the polymer on the properties of the catalyst, PVP was removed from the surface of the particles after their transfer to the support by simultaneous treatment with ozone and UV radiation. This allowed complete cleaning of the catalyst surface from the organic stabilizer without any change in the morphology of particles. The effectiveness of this treatment method was confirmed by X-ray photoelectron spectroscopy and scanning electron microscopy. It was found experimentally that the shape of nanoparticles does not influence the catalyst selectivity, but the activity decreases in the order Pd-oct > Pd-co > Pd-cub. Since octahedrons consist of (111) faces, the cubes contain only (100) faces, and the cuboctahedrons are composed of faces of both types, Pd-111 is more active than Pd-100. Calculations with the use of a statistical method showed that the similar to 3-nm Pd octahedrons are nanoparticles with optimum shape and size, giving maximum catalyst activity.