Ethylene hydrogenation on supported Ni, Pd and Pt nanoparticles: Catalyst activity, deactivation and the d-band model

Keywords: Model catalysis Nickel Palladium Platinum d-band Ethylene de-/hydrogenation a b s t r a c t Ethylene hydrogenation catalyzed at 300 K by 1–1.5 nm nanoparticles of Ni, Pd and Pt supported on MgO (1 0 0) with a narrow size-distribution, as well as the deactivation under reaction conditions at 400 K, was investigated with pulsed molecular beam experiments. Ni nanoparticles deactivate readily at 300 K, whereas Pd particles deactivate only after pulsing at 400 K, and Pt particles were found to retain hydro-genation activity even after the 400 K heating step. The hydrogenation turnover frequency normalized to the number of particles exhibited the trend, Pt > Pd > Ni. The activity/deactivation was found to scale with the location of the particles' d-band centroid, e c , with respect to the Fermi energy of the respective metals calculated with density-functional theory. An e c closer to the Fermi level is indicative of a facile deactivation/low activity and an e c farther from the Fermi level is characteristic of higher activity/ impeded deactivation. CO adsorption, probed with infrared reflection absorption spectroscopy was used to investigate the clusters before and after the reaction, and the spectral features correlated with the observed catalytic behavior. The correlation between the electronic structure and the catalytic activity of materials is one of the fundamental principles underlying the understanding, and systematization of investigations in heterogeneous catalysis. It is also a powerful aid in the selection and design of catalysts, and the interpretation of trends measured across the periodic table. For transition metal catalysts, the d-band model has been particularly useful in investigating and systematizing the above correlation [1–3]. For model heterogeneous catalysis, ethylene hydrogenation represents the most basic hydrogenation reaction catalyzed by noble metals and as such it has been thoroughly investigated on Ni, Pd, and Pt single crystals [4–11], small particles [12–17], as well as a variety of supported metal catalysts [18]. A theoretical study of the ethylene hydrogenation on pseudomorphic Pd films grown on different metal single crystals, employing the d-band model, concluded that the activation barriers for hydrogenation and dehydrogenation depend on the location of the d-band center of the metal catalyst with respect to the Fermi level [19]. Specifically, a d-band center closer to the Fermi level facilitated a lower activation barrier for the dehydrogenation of ethylene to vinyl, and a higher activation barrier for the hydrogenation to ethane. In this letter …