Experimental and Theoretical Investigation of the Restructuring Process Induced by CO at Near Ambient Pressure: Pt Nanoclusters on Graphene/Ir(111)

Abstract

The adsorption of CO on Pt nanoclusters grown in a regular array on a template provided by the graphene/Ir(111) Moiré was investigated by means of infrared-visible sum frequency generation vibronic spectroscopy, scanning tunneling microscopy, X-ray photoelectron spectroscopy from ultrahigh vacuum to near-ambient pressure, and ab initio simulations. Both terminally and bridge bonded CO species populate nonequivalent sites of the clusters, spanning from first to second-layer terraces to borders and edges, depending on the particle size and morphology and on the adsorption conditions. By combining experimental information and the results of the simulations, we observe a significant restructuring of the clusters. Additionally, above room temperature and at 0.1 mbar, Pt clusters catalyze the spillover of CO to the underlying graphene/Ir(111) interface.

Monitoring the Interaction of CO with Graphene Supported Ir Clusters by Vibrational Spectroscopy and Density Functional Theory Calculations

“…Therefore, only one IR band is present at 2070 cm -1 on 0.2 ML Ir clusters. This feature was also reported by Podda et al25 by observing CO adsorption only in on top of one layer and two layers Pt clusters. In addition, the red shifted shoulder compared to the single crystal metal surface was assigned to more CO adsorption on undercoordinated metal atoms in cluster.CONCLUSIONSThe interaction of carbon monoxide (CO) with clean Ir(111) single crystal surface and different sized Ir clusters on graphene/Ir(111) was studied in detail by employing IRRAS.…”

“…This is consistent with our IR data showing the C-O stretching frequency at 2050 cm -1 for the CO adsorption on single layer clusters, and 2088 cm -1 for the adsorption of CO on mostly two layers high clusters. The blue shift from 2050 cm -1 to 2088 cm -1 for the 1 st layer to 2 nd layer adsorption can be explained by the interaction between CO and Ir cluster originating from the stronger donation from CO 5σ orbital and π-back donation from the 5d orbital of Ir and was observed previously on Pt/graphene/Ir(111) as well25 .The intercalation of CO in graphene is excluded in this work as a full monolayer graphene is grown on Ir(111). IRRAS spectra obtained after exposing Ir clusters to highest CO exposure (60 L) at 195 K. (A) 0.05 ML Ir/graphene/Ir(111) (B) 0.1 ML Ir/graphene/Ir(111) (C) 0.15 ML Ir/graphene/Ir(111) and (D) 0.2 ML Ir/graphene/Ir(111).…”

Computational Design of Clusters for Catalysis

“…The shortcoming of these sintering simulations is the lack of adsorbates, which would necessarily be present in reaction conditions and could influence the stability of the clusters (133,134). In fact, high pressures of H 2 and O 2 can enhance the sintering of metallic nanoclusters (135)(136)(137).…”

Vibrational fingerprint of localized excitons in a two-dimensional metal-organic crystal

“…While following the carbonylation process in situ, we observed the growth of four distinct vibronic features in the C–O stretching region for the 2D FePc/GR crystal, while no such features were observed for the multilayer, as detailed below. A complete bare GR sheet is not active toward CO adsorption and passivates the underlying Ir metal surface 26 , 27 . Indeed, upon exposure of the bare GR/Ir(111) system to several mbar of CO, IR-Vis SFG still detects only the GR phonon at 1608 cm −1 , corresponding to the in-plane optical G modes associated with the stretching of the pairs of sp 2 -bonded C atoms 28 , while no C–O stretching is observed (Supplementary Fig.…”

“…1 ). Intercalation of CO under the GR sheet would produce a very intense vibronic signal in the 2040–2080 cm −1 range 26 . Instead, on the 2D FePc/GR/Ir(111) crystal features associated with the C–O stretch progressively develop in the 2000 cm −1 region for CO pressure above 1 mbar at room temperature.…”