Hydrogen adsorption and desorption on the Pt and Pd subnano clusters — a review

Abstract

In this review, we present our recent first principles studies on the sequential H2 dissociative chemisorption and H desorption on the Ptn and Pdn clusters (n=2−9, 13). Upon full saturation by H atoms, the calculated H2 dissociative chemisorption energy and H desorption energy on Pt13 and Pd13 clusters are similar to the corresponding values on smaller close-packed clusters. Indeed, the catalytic performances of these subnano clusters do not vary significantly with the particle sizes or shapes. Instead, they are dependent on the surface metal atoms which can be accessed by H atoms. In addition to the coverage dependency of the H2dissociative chemisorption and H sequential desorption energies, the phase transition of both Pt13 and Pd13from the icosahedral to fcc-like structures at certain H coverage was also investigated.

Platinum–hydrogen vibrations and low energy electronic excitations of 13-atom Pt nanoclusters

“…4,13 This is compatible with our own findings. 6 However, the situation is complicated by a possible support-dependent structural transformation as H coverage increases.…”

“…Secondly, spin-orbit coupling plays an important role in heavy elements and has been predicted to garble the energy levels of these systems. 17 expected in open-shell Pt 13 clusters, 4 or also as a consequence of incomplete restructuration on adsorption after desorption. 6 We also note that a nominal hydrogen coverage often represents an average over clusters with slightly different coverages, 6 and the resolution will depend on the details of contributing states.…”

“…12 In order to overcome the experimental deficit relating to H vibrations on Pt clusters, to support the binding geometry of hydrogen on the Pt 13 and to set it in relation to the observations in macroscopic specimens we undertook an infrared spectroscopic study of hydrogen chemisorption on Pt 13 clusters in LTL zeolite.…”

Anomale diamagnetische Suszeptibilität von 13‐atomigen Platin‐Nanocluster‐Superatomen

“…Zudem sind die Unterschiede zu den "on-top" und den dreifach verbrückt gebundenen H-Atomen nicht sehr groß. [14,19] Der H-H-Abstand auf gesättigten Pt-Clustern entspricht etwa 0.22 nm oder 4.7 a 0 . [19] Bei diesem Abstand kommt es zu beträchtlicher Überlappung der H-1s-Elektronen, besonders im hydridischen Zustand, was die Betrachtung der Pt-gebundenen Hydridwasserstoffe als Satz von doppelt besetzten delokalisierten Cluster-Molekülorbitalen genügend rechtfertigt.…”

“…[14,19] Der H-H-Abstand auf gesättigten Pt-Clustern entspricht etwa 0.22 nm oder 4.7 a 0 . [19] Bei diesem Abstand kommt es zu beträchtlicher Überlappung der H-1s-Elektronen, besonders im hydridischen Zustand, was die Betrachtung der Pt-gebundenen Hydridwasserstoffe als Satz von doppelt besetzten delokalisierten Cluster-Molekülorbitalen genügend rechtfertigt. [19] Wird der radiale Abstand dieser Schale vom Clusterzentrum durch die Summe der Pt-Pt-und der Pt-H-Bindungslängen (0.277 nm + 0.158 nm = 0.435 nm) angenähert, erhalten wir einen Beitrag zu c D von À53.5 10 À6 cm 3 pro mol Hydridelektronen.…”