Hydrogenation of ethylene over palladium: Evolution of the catalyst structure by operando synchrotron-based techniques
Palladium-based catalysts are exploited in the industrial scale for selective hydrogenation of hydrocarbons. Formation of palladium carbide and hydride phases under reaction conditions changes the catalytic properties of the material, which points to the importance of operando characterization for determining a relation between the relative fraction of the two phases and the catalyst performance. We present a combined time-resolved characterization by X-ray absorption spectroscopy (in both near-edge and extended regions) and X-ray diffraction of a working palladium-based catalyst during hydrogenation of ethylene in a wide range of partial pressures of ethylene and hydrogen. Synergistic coupling of multiple techniques allowed us to follow the structural evolution of palladium lattice as well as the transitions between metallic, hydride and carbide phases of palladium. Nanometric dimensions of the particles resulted in the considerable contribution of both surface and bulk carbides to the absorption spectra. During reaction, palladium carbide is formed, which does not lead to a loss of activity. Unusual contraction of the unit cell parameter of palladium lattice in a spent catalyst was observed upon increasing hydrogen partial pressure.
- This article is part of the themed collection: Reaction mechanisms in catalysis