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

Abstract

Ethylene hydrogenation catalyzed at 300 K by 1-1.5 nm nanoparticles of Ni, Pd and Pt supported on MgO(100) with a narrow size-distribution, as well as the deactivation under reaction conditions at 400 K, were 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 hydrogenation 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, ε c , with respect to the Fermi energy of the respective metals calculated with density-functional theory. An ε c closer to the Fermi level is indicative of a facile deactivation/low activity and an ε 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.

Fluxionality of Catalytic Clusters: When It Matters and How to Address It

“…On the other hand, the presence of the support would provide certain stabilization of the isomers. Among Pt, Pd, and Ni clusters on MgO under conditions of ethylene hydrogenation at 300 K, Pt clusters were shown to deactivate the least, 44 indicating their higher relative stability in the presence of hydrocarbons and hydrogen. However, adsorbates can also cause cluster dissociation, as is sometimes the case with clusters of Au in the presence of CO. 38 In view of these reports, the likely conclusion can be that the majority of cluster minima are generally easily accessible within a given well on the reaction profile at high temperatures and coverage.…”

Controlling Ethylene Hydrogenation Reactivity on Pt13 Clusters by Varying the Stoichiometry of the Amorphous Silica Support

“…We have recently observed trends that follow the predictions of the d c model in studies of the catalyzed hydrogenation of ethylene on larger nanoparticles of Ni, Pd, and Pt supported on MgO(100), where the disposition for catalyst deactivation was directly related to the calculated d-band center of M 30 (M = Ni, Pd, and Pt) model clusters. [40] Themetal with the d-band center closest to the Fermi level, Ni, exhibited the most facile deactivation whereas the metal with ad -band center farthest from the Fermi level, Pt, was most resistant to deactivation.…”

DFT-Computed Trends in the Properties of Bimetallic Precious Metal Nanoparticles with Core@Shell Segregation

“…Previous work has highlighted clearly the correlation between the d-band centre and adsorption strength very clear for monometallic systems; [39][40][41][42][43][44] however, the inhomogeneous distribution of the constituent elements in bimetallic NPs, such as the case of core@shell segregation, means this standard model needs adaptation. The more complex parameter space, which now includes interfacial strain and charge transfer effects, is most obvious when considering the inconsistencies between our results and the previous slab calculations of Ruban et al.…”

“…Similarly, the relationship of catalytic observables, such as reactivity, to the position of the dband centre [39][40][41][42][43][44] or structural features, such as edges and vertices, 45,46 have been investigated thoroughly for monometallic NPs, but bimetallic NPs are structurally and compositionally more complicated; 47 too simplify the analysis, d-band positioning, and chemical interactions, are often considered using periodic slab models with dopants and/or monolayer coverages of a secondary element probing the property changes. 23,25,48 For unrelaxed slab models, Ruban et al documented shifts in the d-band centre for a range of transition metals; 49 the effect of epitaxial strain on d-band chemistry has been generalised since for bimetallic surfaces, 50,51 with the width of the surface d-band noted as being responsive to structural factors, and the d-band centre downshifting in response to band broadening.…”