Ethylene hydrogenation on supported Pd nanoparticles: Influence of support on catalyst activity and deactivation

Abstract

Palladium based systems are used extensively in a wide range of catalytic hydrogenation reactions. Here, electronic modifications of two amorphous SiO2 thin films are used to influence the properties of supported Pd nanoparticles (≈1 nm). Negative charging of the metal particles leads to destabilization of both, surface and subsurface hydrogen species, whereas positive charging leads to stabilization of both hydrogen species as evidenced by temperature-programmed desorption (TPD) measurements. The impact of this finding for general hydrogenation reactions is illustrated for ethylene hydrogenation at 300 K using a pulsed molecular beam technique, where an increase in turnover frequency (TOF) over one order of magnitude is observed for positively charged particles, compared to negative ones. The difference in hydrogenation TOF can be rationalized by two reasons: (i) increased hydrogen coverage on the metal surface due to stabilization and (ii) reduction in activation barrier for hydrogenation, both caused by metal-support interactions. In addition, the active phase of the metal particles during catalysis is proposed to be influenced by two mechanisms, formation of a carbide phase and a dehydrogenated carbonaceous overlayer on the surface.