Shape-controlled palladium nanoparticles in catalytic hydrogenations

Monodisperse Pd nanocubes of 20 nm rib length and Pd nanospheres of 3 nm diameter deposited on corundum were used as efficient tool to reveal structure sensitivity of three-phase hydrogenations of unsaturated alcohols. For an olefin alcohol hydrogenation in the kinetic regime, surface (100) atoms of the cubes displayed lower activity than other surface atoms of the spheres. Apparent activation energies of 23 kJ/mol for the cubes and 17 kJ/mol for the spheres confirmed the reaction structure sensitivity. In an acetylenic alcohol hydrogenation, the cubes showed higher selectivity to an olefinic product than the spheres. Apparent activation energy was found as 38 kJ/mol for the cubes and 24 kJ/mol for the spheres. The apparent structure sensitivity in this case was attributed to liquid-solid mass transfer limitations governing the sphere-catalyzed reactions. The study shows the applicability and limitations of the use of nanoparticles for structure sensitivity studies in catalysis.