Selective hydrogenation of multi-unsaturated hydrocarbons over nanostructured model supported catalysts

Atomistic–level understanding of surface processes is a key prerequisite for rational design of new catalytic and functional materials. In our studies, we investigate mechanisms, kinetics and thermodynamics of heterogeneously catalyzed reactions and adsorption processes on nanostructured model supported catalysts to provide fundamental insights into the surface chemistry. By employing pulsed multi-molecular beam techniques, infrared reflection-absorption spectroscopy and synchrotron-based spectroscopies on well-defined nanostructured model surfaces (e.g. metallic nanoparticles supported over planar thin oxide films grown on metal single crystals), we study mechanistic details of complex multi-pathway surface reactions, such as hydrocarbon transformation in presence of hydrogen or selective hydrogenation of multi-unsaturated hydrocarbons. The ultimate goal of our research is obtaining detailed correlations between reactivity, selectivity and the particular structure of the catalytic surface.

Specifically, we investigate hydrogenation and isomerization of olefins and α,β-unsaturated ketones over Pd nanoparticles supported on well-defined model Fe3O4/Pt(111) oxide film and Pd(111). By varying structural properties and chemical composition (e.g. by depositing surface modifiers) of model catalysts and performing detailed kinetic investigations, we are aiming at an atomistic-level understanding of hydrocarbon conversions with hydrogen and revealing the role of specific surface sites, such as e.g. low-coordinated surface sites, in competing reaction pathways.

Recently, we have shown that selective hydrogenation of the C=O bond in acrolein to form an unsaturated alcohol is possible over Pd(111) with nearly 100 % selectivity. However, this process was found to require a very distinct modification of the Pd(111) surface with an overlayer of oxopropyl spectator species that are formed from acrolein during the initial stages of reaction and turn the metal surface selective towards propenol formation.

Summary of some recent results on olefin hydrogenation over Pd nanoparticles (for more information see Ludwig et al, J. Catal., 2011, 284, 148-156 and Dostert et. al., J. Amer.Chem.Soc. 137 (2015) 13496–13502 )